nuttx/boards/arm/stm32/stm32f4discovery/README.txt

README
======

This README discusses issues unique to NuttX configurations for the
STMicro STM32F4Discovery development board featuring the STM32F407VGT6
MCU. The STM32F407VGT6 is a 168MHz Cortex-M4 operation with 1Mbit Flash
memory and 128kbytes. The board features:

  - On-board ST-LINK/V2 for programming and debugging,
  - LIS302DL, ST MEMS motion sensor, 3-axis digital output accelerometer,
  - MP45DT02, ST MEMS audio sensor, omni-directional digital microphone,
  - CS43L22, audio DAC with integrated class D speaker driver,
  - Four user LEDs and two push-buttons,
  - USB OTG FS with micro-AB connector, and
  - Easy access to most MCU pins.

Refer to http://www.st.com/internet/evalboard/product/252419.jsp for
further information about this board.

NOTE: This port was developed on the original board, order code
STM32F4DISCOVERY.  That board has been replaced with the new order code
STM32F407VG-DISC1.  The new version of the board differs in at least these
ways:

  - The ST-LINK/V2 has been updated to ST-LINK/V2-A on STM32F407G-DISC1
    with a Virtual Com port and Mass storage.
  - LIS3DSH ST MEMS 3-axis accelerometer

Contents
========

  - LEDs
  - RGB LED Driver
  - PWM
  - UARTs
  - Timer Inputs/Outputs
  - Nintendo Wii Nunchuck
  - Quadrature Encoder
  - FPU
  - STM32F4DIS-BB
  - SSD1289
  - UG-2864AMBAG01 / UG-2864HSWEG01
  - HCI UART
  - STM32F4Discovery-specific Configuration Options
  - BASIC
  - Testing LLVM LIBC++ with NuttX
  - Configurations

LEDs
====

The STM32F4Discovery board has four LEDs; green, orange, red and blue on the
board. These LEDs are not used by the board port unless CONFIG_ARCH_LEDS is
defined.  In that case, the usage by the board port is defined in
include/board.h and src/up_leds.c. The LEDs are used to encode OS-related
events as follows:

  SYMBOL                Meaning                 LED1*    LED2     LED3     LED4
                                                green    orange   red      blue
  -------------------  -----------------------  -------  -------  -------  ------
  LED_STARTED          NuttX has been started   ON       OFF      OFF      OFF
  LED_HEAPALLOCATE     Heap has been allocated  OFF      ON       OFF      OFF
  LED_IRQSENABLED      Interrupts enabled       ON       ON       OFF      OFF
  LED_STACKCREATED     Idle stack created       OFF      OFF      ON       OFF
  LED_INIRQ            In an interrupt**        ON       N/C      N/C      OFF
  LED_SIGNAL           In a signal handler***   N/C      ON       N/C      OFF
  LED_ASSERTION        An assertion failed      ON       ON       N/C      OFF
  LED_PANIC            The system has crashed   N/C      N/C      N/C      ON
  LED_IDLE             STM32 is is sleep mode   (Optional, not used)

  * If LED1, LED2, LED3 are statically on, then NuttX probably failed to boot
    and these LEDs will give you some indication of where the failure was
 ** The normal state is LED3 ON and LED1 faintly glowing.  This faint glow
    is because of timer interrupts that result in the LED being illuminated
    on a small proportion of the time.
*** LED2 may also flicker normally if signals are processed.

RGB LED Driver
==============

Alan Carvalho de Assis has used the STM32F4-Discovery to drive an RGB LED
using PWM output.  The external RGB connected this way:

   R = TIM1 CH1 on PE9
   G = TIM2 CH2 on PA1
   B = TIM3 CH3 on PB0

The RGB LED driver that uses PWM to control the red, green, and blue color
components can be enabled with the following configuratin settings:

  +CONFIG_RGBLED=y

  +CONFIG_PWM

  +CONFIG_STM32_TIM1
  +CONFIG_STM32_TIM2
  +CONFIG_STM32_TIM3
  +CONFIG_STM32_TIM1_PWM=y
  +CONFIG_STM32_TIM1_MODE=0
  +CONFIG_STM32_TIM1_CHANNEL=1
  +CONFIG_STM32_TIM1_CHMODE=0
  +CONFIG_STM32_TIM2_PWM=y
  +CONFIG_STM32_TIM2_MODE=0
  +CONFIG_STM32_TIM2_CHANNEL=2
  +CONFIG_STM32_TIM2_CHMODE=0
  +CONFIG_STM32_TIM3_PWM=y
  +CONFIG_STM32_TIM3_MODE=0
  +CONFIG_STM32_TIM3_CHANNEL=3
  +CONFIG_STM32_TIM3_CHMODE=0

PWM
===

The STM32F4Discovery has no real on-board PWM devices, but the board can be
configured to output a pulse train using TIM4 CH2 on PD3.  This pin is
available next to the audio jack.

UARTs
=====

UART/USART PINS
---------------

USART1
  CK      PA8
  CTS     PA11*
  RTS     PA12*
  RX      PA10*, PB7
  TX      PA9*, PB6*
USART2
  CK      PA4*, PD7
  CTS     PA0*, PD3
  RTS     PA1, PD4*
  RX      PA3, PD6
  TX      PA2, PD5*
USART3
  CK      PB12, PC12*, PD10
  CTS     PB13, PD11
  RTS     PB14, PD12*
  RX      PB11, PC11, PD9
  TX      PB10*, PC10*, PD8
UART4
  RX      PA1, PC11
  TX      PA0*, PC10*
UART5
  RX      PD2
  TX      PC12*
USART6
  CK      PC8, PG7**
  CTS     PG13**, PG15**
  RTS     PG12**, PG8**
  RX      PC7*, PG9**
  TX      PC6, PG14**

 * Indicates pins that have other on-board functions and should be used only
   with care (See table 5 in the STM32F4Discovery User Guide).  The rest are
   free I/O pins.
** Port G pins are not supported by the MCU

Default USART/UART Configuration
--------------------------------

USART2 is enabled in most configurations (see */defconfig).  RX and TX are
configured on pins PA3 and PA2, respectively (see include/board.h).

These pins selections, however, conflict with Ethernet pin usage on the
STM32F4DIS-BB base board.  The STM32F4DIS-BB base board provides RS-232
drivers and a DB9 connector for USART6.  USART6 is the preferred serial
console for use with the STM32F4DIS-BB.

Timer Inputs/Outputs
====================

TIM1
  CH1     PA8, PE9
  CH2     PA9*, PE11
  CH3     PA10*, PE13
  CH4     PA11*, PE14
TIM2
  CH1     PA0*, PA15, PA5*
  CH2     PA1, PB3*
  CH3     PA2, PB10*
  CH4     PA3, PB11
TIM3
  CH1     PA6*, PB4, PC6
  CH2     PA7*, PB5, PC7*
  CH3     PB0, PC8
  CH4     PB1, PC9
TIM4
  CH1     PB6*, PD12*
  CH2     PB7, PD13*
  CH3     PB8, PD14*
  CH4     PB9*, PD15*
TIM5
  CH1     PA0*, PH10**
  CH2     PA1, PH11**
  CH3     PA2, PH12**
  CH4     PA3, PI0
TIM8
  CH1     PC6, PI5
  CH2     PC7*, PI6
  CH3     PC8, PI7
  CH4     PC9, PI2
TIM9
  CH1     PA2, PE5
  CH2     PA3, PE6
TIM10
  CH1     PB8, PF6
TIM11
  CH1     PB9*, PF7
TIM12
  CH1     PH6**, PB14
  CH2     PC15, PH9**
TIM13
  CH1     PA6*, PF8
TIM14
  CH1     PA7*, PF9

 * Indicates pins that have other on-board functions and should be used only
   with care (See table 5 in the STM32F4Discovery User Guide).  The rest are
   free I/O pins.
** Port H pins are not supported by the MCU

Nintendo Wii Nunchuck:
======================

  There is a driver on NuttX to support Nintendo Wii Nunchuck Joystick. If you
  want to use it please select these options:

  - Enable the I2C1 at System Type -> STM32 Peripheral Support, it will enable:

    CONFIG_STM32_I2C1=y

  - Enable to Custom board/driver initialization at RTOS Features -> RTOS hooks

    CONFIG_BOARD_LATE_INITIALIZE=y

  - Enable the I2C Driver Support at Device Drivers, it will enable this symbol:

    CONFIG_I2C=y

  - Nintendo Wii Nunchuck Joystick at Device Drivers -> [*] Input Device Support

    CONFIG_INPUT=y
      CONFIG_INPUT_NUNCHUCK=y

  - Enable the Nunchuck joystick example at Application Configuration -> Examples

  CONFIG_EXAMPLES_NUNCHUCK=y
    CONFIG_EXAMPLES_NUNCHUCK_DEVNAME="/dev/nunchuck0"

  You need to connect GND and +3.3V pins from Nunchuck connector to GND and 3V
  of stm32f4discovery respectively (Nunchuck also can work connected to 5V, but
  I don't recommend it). Connect I2C Clock from Nunchuck to SCK (PB6) and the
  I2C Data to SDA (PB9).

Quadrature Encoder:
===================

  The nsh configuration has been used to test the Quadrture Encoder
  (QEncoder, QE) with the following modifications to the configuration
  file:

  - These setting enable support for the common QEncode upper half driver:

   CONFIG_BOARD_LATE_INITIALIZE=y

   CONFIG_SENSORS=y
     CONFIG_SENSORS_QENCODER=y

  - The timer 2 needs to be enabled:

  CONFIG_STM32_TIM2=y

  - This is a board setting that selected timer 2 for use with the
    quadrature encode:

    CONFIG_STM32F4DISCO_QETIMER=2

  - These settings enable the STM32 Quadrature encoder on timer 2:

    CONFIG_STM32_TIM2_QE=y
    CONFIG_STM32_TIM4_QECLKOUT=2800000
    CONFIG_STM32_QENCODER_FILTER=y
    CONFIG_STM32_QENCODER_SAMPLE_EVENT_6=y
    CONFIG_STM32_QENCODER_SAMPLE_FDTS_4=y

  - These settings enable the test case at apps/examples/qencoder:

    CONFIG_EXAMPLES_QENCODER=y
    CONFIG_EXAMPLES_QENCODER_DELAY=100
    CONFIG_EXAMPLES_QENCODER_DEVPATH="/dev/qe0"

  In this configuration, the QEncoder inputs will be on the TIM2 inputs of
  PA15 and PA1 (CH1 and CH2 respectively).

  You can also use QEncoder with other timers, but keep in mind that only TIM2
  and TIM5 are 32bits timers, all other timers are 16-bit then the QE counter
  will overflow after 65535.

  If TIM4 is selected, then PB6 and PB7 will be used for CH1 and CH2.
  If TIM8 is selected, then PC6 and PI5 will be used for CH1 and CH2.

FPU
===

FPU Configuration Options
-------------------------

There are two version of the FPU support built into the STM32 port.

1. Non-Lazy Floating Point Register Save

   In this configuration floating point register save and restore is
   implemented on interrupt entry and return, respectively.  In this
   case, you may use floating point operations for interrupt handling
   logic if necessary.  This FPU behavior logic is enabled by default
   with:

     CONFIG_ARCH_FPU=y

2. Lazy Floating Point Register Save.

   An alternative mplementation only saves and restores FPU registers only
   on context switches.  This means: (1) floating point registers are not
   stored on each context switch and, hence, possibly better interrupt
   performance.  But, (2) since floating point registers are not saved,
   you cannot use floating point operations within interrupt handlers.

   This logic can be enabled by simply adding the following to your .config
   file:

     CONFIG_ARCH_FPU=y
     CONFIG_ARMV7M_LAZYFPU=y

CFLAGS
------

Only recent GCC toolchains have built-in support for the Cortex-M4 FPU.  You will see
the following lines in each Make.defs file:

  ifeq ($(CONFIG_ARCH_FPU),y)
    ARCHCPUFLAGS = -mcpu=cortex-m4 -mthumb -march=armv7e-m -mfpu=fpv4-sp-d16 -mfloat-abi=hard
  else
    ARCHCPUFLAGS = -mcpu=cortex-m3 -mthumb -mfloat-abi=soft
  endif

Configuration Changes
---------------------

Below are all of the configuration changes that I had to make to boards/stm3240g-eval/nsh2
in order to successfully build NuttX using the Atollic toolchain WITH FPU support:

  -CONFIG_ARCH_FPU=n              : Enable FPU support
  +CONFIG_ARCH_FPU=y

  -CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y   : Disable the CodeSourcery toolchain
  +CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=n

  -CONFIG_ARMV7M_TOOLCHAIN_ATOLLIC=n         : Enable the Atollic toolchain
  +CONFIG_ARMV7M_TOOLCHAIN_ATOLLIC=y        :

  -CONFIG_INTELHEX_BINARY=y       : Suppress generation FLASH download formats
  +CONFIG_INTELHEX_BINARY=n       : (Only necessary with the "Lite" version)

  -CONFIG_HAVE_CXX=y              : Suppress generation of C++ code
  +CONFIG_HAVE_CXX=n              : (Only necessary with the "Lite" version)

See the section above on Toolchains, NOTE 2, for explanations for some of
the configuration settings.  Some of the usual settings are just not supported
by the "Lite" version of the Atollic toolchain.

STM32F4DIS-BB
=============

On-board PIO usage:

  ---------- ------------- ------------------------------
  PIO        SIGNAL        FUNCTION
  ---------- ------------- ------------------------------
  PB11       TXEN          LAN8720
  PB12       TXD0
  PB13       TXD1
  PC4        RXD0/MODE0
  PC5        RXD1/MODE1
  PA7        RXDR/PHYAD0
  PA2        MDIO
  PC1        MDC
  PA1        NINT/REFCLK0
  PE2        NRST
  ---------- ------------- ------------------------------
  PC6        D2            DCMI
  PC7        D3
  PE0        D4
  PE1        D5
  PE4        D6
  PB6        D7
  PE5        D8
  PE6        D9
  PA6        PCLK
  PA4        HS
  PB7        VS
  PD6        PWR_EN
  PD12       RST
  PB9        SDA
  PB8        SCL
  ---------- ------------- ------------------------------
  USART6_TX  T1IN          SP3232EEY-L
  USART6_RX  T2OUT
  ---------- ------------- ------------------------------
  PB15       NCD           MicroSD
  PC9        DAT1
  PC8        DAT0
  PC12       CLK
  PD2        CMD
  PC11       CD/DAT3
  PC10       DAT2
  ---------- ------------- ------------------------------

SSD1289
=======

I purchased an LCD display on eBay from China.  The LCD is 320x240 RGB565 and
is based on an SSD1289 LCD controller and an XPT2046 touch IC.  The pin out
from the 2x16 connect on the LCD is labelled as follows:

LCD CONNECTOR:          SSD1289 MPU INTERFACE PINS:

   +------+------+      DEN     I  Display enable pin
1  | GND  | 3V3  |  2   VSYNC   I  Frame synchronization signal
   +------+------+      HSYNC   I  Line synchronization signal
3  | D1   | D0   |  4   DOTCLK  I  Dot clock and OSC source
   +------+------+      DC      I  Data or command
5  | D3   | D2   |  6   E (~RD) I  Enable/Read strobe
   +------+------+      R (~WR) I  Read/Write strobe
7  | D5   | D4   |  8   D0-D17  IO For parallel mode, 8/9/16/18 bit interface
   +------+------+      WSYNC   O  RAM write synchronizatin output
9  | D7   | D6   | 10   ~RES    I  System reset
   +------+------+      ~CS     I  Chip select of serial interface
11 | D9   | D8   | 12   SCK     I  Clock of serial interface
   +------+------+      SDI     I  Data input in serial mode
13 | D11  | D10  | 14   SDO     O  Data output in serial moce
   +------+------+
15 | D13  | D12  | 16
   +------+------+
17 | D15  | D14  | 18
   +------+------+
19 | RS   | CS   | 20
   +------+------+
21 | RD   | WR   | 22  NOTES:
   +------+------+
23 |BL_CNT|RESET | 24  BL_CNT is the PWM backlight level control.
   +------+------+
25 |TP_RQ |TP_S0 | 26  These pins are for the touch panel: TP_REQ
   +------+------+     TP_S0, TP_SI, TP_SCX, and TP_CS
27 | NC   |TP_SI | 28
   +------+------+
29 | NC   |TP_SCX| 30
   +------+------+
31 | NC   |TP_CS | 32
   +------+------+

MAPPING TO STM32 F4:

  ---------------- -------------- ----------------------------------
   STM32 FUNCTION  LCD PIN       STM32F4Discovery PIN
  ---------------- -------------- ----------------------------------
   FSMC_D0          D0     pin 4   PD14 P1 pin 46 Conflict (Note 1)
   FSMC_D1          D1     pin 3   PD15 P1 pin 47 Conflict (Note 2)
   FSMC_D2          D2     pin 6   PD0  P2 pin 36 Free I/O
   FSMC_D3          D3     pin 5   PD1  P2 pin 33 Free I/O
   FSMC_D4          D4     pin 8   PE7  P1 pin 25 Free I/O
   FSMC_D5          D5     pin 7   PE8  P1 pin 26 Free I/O
   FSMC_D6          D6     pin 10  PE9  P1 pin 27 Free I/O
   FSMC_D7          D7     pin 9   PE10 P1 pin 28 Free I/O
   FSMC_D8          D8     pin 12  PE11 P1 pin 29 Free I/O
   FSMC_D9          D9     pin 11  PE12 P1 pin 30 Free I/O
   FSMC_D10         D10    pin 14  PE13 P1 pin 31 Free I/O
   FSMC_D11         D11    pin 13  PE14 P1 pin 32 Free I/O
   FSMC_D12         D12    pin 16  PE15 P1 pin 33 Free I/O
   FSMC_D13         D13    pin 15  PD8  P1 pin 40 Free I/O
   FSMC_D14         D14    pin 18  PD9  P1 pin 41 Free I/O
   FSMC_D15         D15    pin 17  PD10 P1 pin 42 Free I/O
   FSMC_A16         RS     pin 19  PD11 P1 pin 27 Free I/O
   FSMC_NE1         ~CS    pin 10  PD7  P2 pin 27 Free I/O
   FSMC_NWE         ~WR    pin 22  PD5  P2 pin 29 Conflict (Note 3)
   FSMC_NOE         ~RD    pin 21  PD4  P2 pin 32 Conflict (Note 4)
   PC6              RESET  pin 24  PC6  P2 pin 47 Free I/O
   Timer ouput      BL_CNT pin 23  (to be determined)
  ---------------- -------------- ----------------------------------

   1 Used for the RED LED
   2 Used for the BLUE LED
   3 Used for the RED LED and for OTG FS Overcurrent.  It may be okay to use
     for the parallel interface if PC0 is held high (or floating).  PC0 enables
     the STMPS2141STR IC power switch that drives the OTG FS host VBUS.
   4 Also the reset pin for the CS43L22 audio Codec.

NOTE:  The configuration to test this LCD configuration is available at
boards/stm32f4discovery/nxlines.  As of this writing, I have not seen the
LCD working so I probably have some things wrong.

I might need to use a bit-banging interface.  Below is the pin configuration
of a similar LCD to support a (write-only), bit banging interface:

  LCD PIN   BOARD CONNECTION
  LEDA      5V
  VCC       5V
  RD        3.3V
  GND       GND
  DB0-7     Port C pins configured as outputs
  DB8-15    Port A pins configured as outputs
  RS        Pin configured as output
  WR        Pin configured as output
  CS        Pin configured as output
  RSET      Pin configured as output

The following summarize the bit banging operations:

  /* Rese the LCD */
  void Reset(void)
  {
    Set RSET output
    delay
    Clear RSET output
    delay
    Set RSET output
  }

  /* Write 16-bits of whatever */
  void Write16(uint8_t ms, uint8_t ls)
  {
    Set port A to ms
    Set port B to ls

    Clear WR pin
    Set   WR pin
  }

  /* Set the index register to an LCD register address */
  void Index(uint8_t address)
  {
    Clear RS
    Write16(0, address);
  }

  /* Write data to the LCD register or GRAM memory */
  void WriteData(uin16_t data)
  {
    Set RS
    Write16(data >> 8, data & 0xff);
  }

  /* Write to a register */
  void WriteRegister(uint8_t address, uint16_t data)
  {
    Index(address);
    WriteData(data);
  }

UG-2864AMBAG01 / UG-2864HSWEG01
===============================

I purchased an OLED display on eBay.  The OLED is 128x64 monochrome and
is based on an UG-2864AMBAG01 OLED controller.  The OLED can run in either
parallel or SPI mode.  I am using SPI mode.  In SPI mode, the OLED is
write only so the driver keeps a 128*64/8 = 1KB framebuffer to remember
the display contents:

Here is how I have the OLED connected.  But you can change this with the
settings in include/board.h and src/stm324fdiscovery.h.  Connector
pinout for the UG-2864AMBAG01 is specific to the theO.net display board
that I am using:

  --------------------------+----------------------------------------------
  Connector CON10 J1:       | STM32F4Discovery
  --------------+-----------+----------------------------------------------
  CON10 J1:     | CON20 J2: | P1/P2:
  --------------+-----------+----------------------------------------------
  1  3v3        | 3,4 3v3   | P2 3V
  3  /RESET     | 8 /RESET  | P2 PB6 (Arbitrary selection)
  5  /CS        | 7 /CS     | P2 PB7 (Arbitrary selection)
  7  A0         | 9 A0      | P2 PB8 (Arbitrary selection)
  9  LED+ (N/C) | -----     | -----
  2  5V Vcc     | 1,2 Vcc   | P2 5V
  4  DI         | 18 D1/SI  | P1 PA7 (GPIO_SPI1_MOSI == GPIO_SPI1_MOSI_1 (1))
  6  SCLK       | 19 D0/SCL | P1 PA5 (GPIO_SPI1_SCK == GPIO_SPI1_SCK_1 (1))
  8  LED- (N/C) | -----     | ------
  10 GND        | 20 GND    | P2 GND
  --------------+-----------+----------------------------------------------
  (1) Required because of on-board MEMS
  -------------------------------------------------------------------------

Darcy Gong recently added support for the UG-2864HSWEG01 OLED which is also
an option with this configuration.  I have little technical information about
the UG-2864HSWEG01 interface (see boards/stm32f4discovery/src/up_ug2864hsweg01.c).

HCI UART
========

BT860
-----

  I have been testing with the DVK_BT960_SA board via J10 as follows:

    DVK_BT860-SA J10     STM32F4 Discovery P1
    pin 1  GND                             P1 pin 49
    pin 2  Module_RTS_O  USART3_CTS PB13,  P1 pin 37
    pin 3  N/C
    pin 4  Module_RX_I   USART3_TXD PB10,  P1 pin 34
    pin 5  Module_TX_O   USART3_RX  PB11,  P1 pin 35
    pin 6  Module_CTS_I  USART3_RTS PB14,  P1 pin 38

  Due to conflicts, USART3 many not be used if Ethernet is enabled with
  the STM32F4DIS-BB base board:

    PB-11 conflicts with Ethernet TXEN
    PB-13 conflicts with Ethernet TXD1

  If you need to use the HCI uart with Ethernet, then you will need to
  configure a new U[S]ART and/or modify the pin selections in
  include/board.h.

CC2564
------

  [To be provided]

  One confusing thing compared with the BT860 is in the naming of the pins
  at the 4-pin RS232 TTL interface:  The BT860 uses BT860-centric naming,
  the Rx pin is for BT860 receive and needs to connect with the STM32 Tx
  pin, the Tx pin is for BT860 transmit an needs to be connected with the
  STM32 Rx pin, etc.  The CC2564, on the hand, uses host-centric naming so
  that the CC2564 Rx pin connects to the STM32 Rx pin, Tx to Tx pin, etc.

Troubleshooting
---------------

  First you should enable CONFIG_DEBUG_WIRELESS_ERR, WARN, and INFO options
  so that you can see what the driver is doing.

  The bring-up problems that I encountered mostly involved setting up the
  4-wire UART interface:  Remember to cross Rx/Tx and RTS/CTS.  The active
  state for RTS and CTS is low.  For bringup of the BT860, I used a Seleae
  logic analyzer connected to the Tx, Rx, RTS, and CTS pins.  When the
  BT860 is working correctly you would see this:

    1. All signals high initially,
    2. When NuttX starts, RTS goes low
    3. The BT860 sees RTS go low and responds by setting CTS low after a
       delay.  This is when it selects between USB and UART.
    4. After another delay, the STM32 sends the 4 Tx bytes.
    5. The BT860 responds with 3 bytes.
    6. If successful, additional commands and responses follow.

  Some of these steps may be different for other HCI UARTs. Steps 4-5 are
  the reset sequence.  the 4 Tx bytes comes from the code in the function
  hci_initialize() in the file wireless/bluetooth/bt_hcicore.c:

    /* Send HCI_RESET */

    bt_hci_cmd_send(BT_HCI_OP_RESET, NULL);

  The code is actually working one command ahead.  It has already queued up
  the reset command and is requesting the HCI UART device features while the
  reset command is being sent:

    ret = bt_hci_cmd_send_sync(BT_HCI_OP_READ_LOCAL_FEATURES, NULL, &rsp);
    if (ret < 0)
      {
        wlerr("ERROR:  bt_hci_cmd_send_sync failed: %d\n", ret);
        return ret;
      }

  A common failure is to see a timeout error (-116) due to a Tx flow control
  failure (CTS is high).  There is no timeout on the first command, the
  timeout actually occurs on the second command in bt_hci_cmd_send_sync():

     do
       {
         /* The timed wait could also be awakened by a signal */

         ret = nxsem_timedwait(&sync_sem, &abstime);
       }
     while (ret == -EINTR);

  The above times out and generates the 116 error.

  In the case of the timeout, the second command is stuck in the message queue
  is never processed because the Tx thread is waiting for the BT_HCI_OP_RESET
  command to complete.  It is blocked in hci_tx_thread() kernel thread.

  The Tx occurs on a kernel thread.  The Tx send of the first command causes
  the hci_tx_kthread() to block.  It waits here until what the HCI UART
  receives the command and responses with the command complete event:

  /* Wait until ncmd > 0 */

    do
      {
        ret = nxsem_wait(&g_btdev.ncmd_sem);
      }
    while (ret == -EINTR);

  bt_hci_cmd_send() will block on the first BT_HCI_OP_RESET until until it
  gets the 3-byte event (BT_EVT) that indicates that the command was
  completed and provides the command status. See the function
  hci_command_complete() where it posts g_btdev.ncmd_sem.

    g_btdev.ncmd = 1;
    nxsem_post(&g_btdev.ncmd_sem);

  You can see such a hange in the wireless debug output

    bt_hci_cmd_send: opcode 0c03 len 3                          <<< BT_HCI_OP_RESET command is queue
    hci_tx_kthread: Sending command 0c03 buf 20002a40 to driver <<< Sent to driver from the Tx thread
    hciuart_write: config 801d924 buffer 20002760 buflen 4      <<< Goes to STM32 HCI UART driver

    bt_hci_cmd_send_sync: opcode 1003 len 3                     <<< next command is queued.
    hciuart_copytotxfifo: txhead 1 txtail 4 nbytes 1            <<< One byte of first command written to Tx HR
    hciuart_enableints: CR1 000020ac CR2 00000301               <<< Tx interrupts enabled

!!!! No Tx interrupts, probably because of Tx flow control (CTS is high) !!!

    hci_initialize: ERROR:  bt_hci_cmd_send_sync failed: -116   <<< Times out on second message

STM32F4Discovery-specific Configuration Options
===============================================

    CONFIG_ARCH - Identifies the arch/ subdirectory.  This should
       be set to:

       CONFIG_ARCH=arm

    CONFIG_ARCH_family - For use in C code:

       CONFIG_ARCH_ARM=y

    CONFIG_ARCH_architecture - For use in C code:

       CONFIG_ARCH_CORTEXM4=y

    CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory

       CONFIG_ARCH_CHIP=stm32

    CONFIG_ARCH_CHIP_name - For use in C code to identify the exact
       chip:

       CONFIG_ARCH_CHIP_STM32F407VG=y

    CONFIG_ARCH_BOARD_STM32_CUSTOM_CLOCKCONFIG - Enables special STM32 clock
       configuration features.

       CONFIG_ARCH_BOARD_STM32_CUSTOM_CLOCKCONFIG=n

    CONFIG_ARCH_BOARD - Identifies the boards/ subdirectory and
       hence, the board that supports the particular chip or SoC.

       CONFIG_ARCH_BOARD=STM32F4Discovery (for the STM32F4Discovery development board)

    CONFIG_ARCH_BOARD_name - For use in C code

       CONFIG_ARCH_BOARD_STM32F4_DISCOVERY=y

    CONFIG_ARCH_LOOPSPERMSEC - Must be calibrated for correct operation
       of delay loops

    CONFIG_ENDIAN_BIG - define if big endian (default is little
       endian)

    CONFIG_RAM_SIZE - Describes the installed RAM

       CONFIG_RAM_SIZE=0x00010000 (64Kb)

    CONFIG_RAM_START - The start address of installed RAM

       CONFIG_RAM_START=0x20000000

    CONFIG_STM32_CCMEXCLUDE - Exclude CCM SRAM from the HEAP

    CONFIG_ARCH_FPU - The STM32F4Discovery supports a floating point unit (FPU)

       CONFIG_ARCH_FPU=y

    CONFIG_ARCH_LEDS - Use LEDs to show state. Unique to boards that
       have LEDs

    CONFIG_ARCH_INTERRUPTSTACK - This architecture supports an interrupt
       stack. If defined, this symbol is the size of the interrupt
        stack in bytes.  If not defined, the user task stacks will be
      used during interrupt handling.

    CONFIG_ARCH_STACKDUMP - Do stack dumps after assertions

    CONFIG_ARCH_LEDS -  Use LEDs to show state. Unique to board architecture.

  Individual subsystems can be enabled:

    AHB1
    ----
    CONFIG_STM32_CRC
    CONFIG_STM32_BKPSRAM
    CONFIG_STM32_CCMDATARAM
    CONFIG_STM32_DMA1
    CONFIG_STM32_DMA2
    CONFIG_STM32_ETHMAC
    CONFIG_STM32_OTGHS

    AHB2
    ----
    CONFIG_STM32_DCMI
    CONFIG_STM32_CRYP
    CONFIG_STM32_HASH
    CONFIG_STM32_RNG
    CONFIG_STM32_OTGFS

    AHB3
    ----
    CONFIG_STM32_FSMC

    APB1
    ----
    CONFIG_STM32_TIM2
    CONFIG_STM32_TIM3
    CONFIG_STM32_TIM4
    CONFIG_STM32_TIM5
    CONFIG_STM32_TIM6
    CONFIG_STM32_TIM7
    CONFIG_STM32_TIM12
    CONFIG_STM32_TIM13
    CONFIG_STM32_TIM14
    CONFIG_STM32_WWDG
    CONFIG_STM32_IWDG
    CONFIG_STM32_SPI2
    CONFIG_STM32_SPI3
    CONFIG_STM32_USART2
    CONFIG_STM32_USART3
    CONFIG_STM32_UART4
    CONFIG_STM32_UART5
    CONFIG_STM32_I2C1
    CONFIG_STM32_I2C2
    CONFIG_STM32_I2C3
    CONFIG_STM32_CAN1
    CONFIG_STM32_CAN2
    CONFIG_STM32_DAC1
    CONFIG_STM32_DAC2
    CONFIG_STM32_PWR -- Required for RTC

    APB2
    ----
    CONFIG_STM32_TIM1
    CONFIG_STM32_TIM8
    CONFIG_STM32_USART1
    CONFIG_STM32_USART6
    CONFIG_STM32_ADC1
    CONFIG_STM32_ADC2
    CONFIG_STM32_ADC3
    CONFIG_STM32_SDIO
    CONFIG_STM32_SPI1
    CONFIG_STM32_SYSCFG
    CONFIG_STM32_TIM9
    CONFIG_STM32_TIM10
    CONFIG_STM32_TIM11

  Timer devices may be used for different purposes.  One special purpose is
  to generate modulated outputs for such things as motor control.  If CONFIG_STM32_TIMn
  is defined (as above) then the following may also be defined to indicate that
  the timer is intended to be used for pulsed output modulation, ADC conversion,
  or DAC conversion. Note that ADC/DAC require two definition:  Not only do you have
  to assign the timer (n) for used by the ADC or DAC, but then you also have to
  configure which ADC or DAC (m) it is assigned to.

    CONFIG_STM32_TIMn_PWM   Reserve timer n for use by PWM, n=1,..,14
    CONFIG_STM32_TIMn_ADC   Reserve timer n for use by ADC, n=1,..,14
    CONFIG_STM32_TIMn_ADCm  Reserve timer n to trigger ADCm, n=1,..,14, m=1,..,3
    CONFIG_STM32_TIMn_DAC   Reserve timer n for use by DAC, n=1,..,14
    CONFIG_STM32_TIMn_DACm  Reserve timer n to trigger DACm, n=1,..,14, m=1,..,2

  For each timer that is enabled for PWM usage, we need the following additional
  configuration settings:

    CONFIG_STM32_TIMx_CHANNEL - Specifies the timer output channel {1,..,4}

  NOTE: The STM32 timers are each capable of generating different signals on
  each of the four channels with different duty cycles.  That capability is
  not supported by this driver:  Only one output channel per timer.

  JTAG Enable settings (by default only SW-DP is enabled):

    CONFIG_STM32_JTAG_FULL_ENABLE - Enables full SWJ (JTAG-DP + SW-DP)
    CONFIG_STM32_JTAG_NOJNTRST_ENABLE - Enables full SWJ (JTAG-DP + SW-DP)
      but without JNTRST.
    CONFIG_STM32_JTAG_SW_ENABLE - Set JTAG-DP disabled and SW-DP enabled

  STM32F4Discovery specific device driver settings

    CONFIG_U[S]ARTn_SERIAL_CONSOLE - selects the USARTn (n=1,2,3) or UART
           m (m=4,5) for the console and ttys0 (default is the USART1).
    CONFIG_U[S]ARTn_RXBUFSIZE - Characters are buffered as received.
       This specific the size of the receive buffer
    CONFIG_U[S]ARTn_TXBUFSIZE - Characters are buffered before
       being sent.  This specific the size of the transmit buffer
    CONFIG_U[S]ARTn_BAUD - The configure BAUD of the UART.  Must be
    CONFIG_U[S]ARTn_BITS - The number of bits.  Must be either 7 or 8.
    CONFIG_U[S]ARTn_PARTIY - 0=no parity, 1=odd parity, 2=even parity
    CONFIG_U[S]ARTn_2STOP - Two stop bits

  STM32F4Discovery CAN Configuration

    CONFIG_CAN - Enables CAN support (one or both of CONFIG_STM32_CAN1 or
      CONFIG_STM32_CAN2 must also be defined)
    CONFIG_CAN_EXTID - Enables support for the 29-bit extended ID.  Default
      Standard 11-bit IDs.
    CONFIG_CAN_FIFOSIZE - The size of the circular buffer of CAN messages.
      Default: 8
    CONFIG_CAN_NPENDINGRTR - The size of the list of pending RTR requests.
      Default: 4
    CONFIG_CAN_LOOPBACK - A CAN driver may or may not support a loopback
      mode for testing. The STM32 CAN driver does support loopback mode.
    CONFIG_STM32_CAN1_BAUD - CAN1 BAUD rate.  Required if CONFIG_STM32_CAN1
      is defined.
    CONFIG_STM32_CAN2_BAUD - CAN1 BAUD rate.  Required if CONFIG_STM32_CAN2
      is defined.
    CONFIG_STM32_CAN_TSEG1 - The number of CAN time quanta in segment 1.
      Default: 6
    CONFIG_STM32_CAN_TSEG2 - the number of CAN time quanta in segment 2.
      Default: 7
    CONFIG_STM32_CAN_REGDEBUG - If CONFIG_DEBUG_FEATURES is set, this will generate an
      dump of all CAN registers.

  STM32F4Discovery SPI Configuration

    CONFIG_STM32_SPI_INTERRUPTS - Select to enable interrupt driven SPI
      support. Non-interrupt-driven, poll-waiting is recommended if the
      interrupt rate would be to high in the interrupt driven case.
    CONFIG_STM32_SPI_DMA - Use DMA to improve SPI transfer performance.
      Cannot be used with CONFIG_STM32_SPI_INTERRUPT.

  STM32F4Discovery DMA Configuration

    CONFIG_SDIO_DMA - Support DMA data transfers.  Requires CONFIG_STM32_SDIO
      and CONFIG_STM32_DMA2.
    CONFIG_STM32_SDIO_PRI - Select SDIO interrupt prority.  Default: 128
    CONFIG_STM32_SDIO_DMAPRIO - Select SDIO DMA interrupt priority.
      Default:  Medium
    CONFIG_STM32_SDIO_WIDTH_D1_ONLY - Select 1-bit transfer mode.  Default:
      4-bit transfer mode.

  STM32 USB OTG FS Host Driver Support

  Pre-requisites

   CONFIG_USBDEV          - Enable USB device support
   CONFIG_USBHOST         - Enable USB host support
   CONFIG_STM32_OTGFS     - Enable the STM32 USB OTG FS block
   CONFIG_STM32_SYSCFG    - Needed
   CONFIG_SCHED_WORKQUEUE - Worker thread support is required

  Options:

   CONFIG_STM32_OTGFS_RXFIFO_SIZE - Size of the RX FIFO in 32-bit words.
     Default 128 (512 bytes)
   CONFIG_STM32_OTGFS_NPTXFIFO_SIZE - Size of the non-periodic Tx FIFO
     in 32-bit words.  Default 96 (384 bytes)
   CONFIG_STM32_OTGFS_PTXFIFO_SIZE - Size of the periodic Tx FIFO in 32-bit
     words.  Default 96 (384 bytes)
   CONFIG_STM32_OTGFS_DESCSIZE - Maximum size of a descriptor.  Default: 128
   CONFIG_STM32_OTGFS_SOFINTR - Enable SOF interrupts.  Why would you ever
     want to do that?
   CONFIG_STM32_USBHOST_REGDEBUG - Enable very low-level register access
     debug.  Depends on CONFIG_DEBUG_FEATURES.
   CONFIG_STM32_USBHOST_PKTDUMP - Dump all incoming and outgoing USB
     packets. Depends on CONFIG_DEBUG_FEATURES.

BASIC
=====
  I have used the stm32f4discovery/nsh configuration to test Michael Haardt's
  BASIC interpreter that you can find at apps/interpreters/bas.

    Bas is an interpreter for the classic dialect of the programming language
    BASIC.  It is pretty compatible to typical BASIC interpreters of the 1980s,
    unlike some other UNIX BASIC interpreters, that implement a different
    syntax, breaking compatibility to existing programs.  Bas offers many ANSI
    BASIC statements for structured programming, such as procedures, local
    variables and various loop types.  Further there are matrix operations,
    automatic LIST indentation and many statements and functions found in
    specific classic dialects.  Line numbers are not required.

  There is also a test suite for the interpreter that can be found at
  apps/examples/bastest.

  Configuration
  -------------
  Below are the recommended configuration changes to use BAS with the
  stm32f4discovery/nsh configuration:

  Dependencies:
    CONFIG_LIBC_EXECFUNCS=y      : exec*() functions are required
    CONFIG_LIBM=y                : Some floating point library is required
    CONFIG_LIBC_FLOATINGPOINT=y  : Floating point printing support is required
    CONFIG_LIBC_TMPDIR="/tmp"    : Writable temporary files needed for some commands
    CONFIG_FS_FAT=y              : With FAT you create a RAMDISK at /tmp
    CONFIG_FAT_LFN=y             : FAT is difficult to use with long file names

  Enable the BASIC interpreter.  Other default options should be okay:
    CONFIG_INTERPRETERS_BAS=y    : Enables the interpreter
    CONFIG_INTERPRETER_BAS_VT100=y

  The BASIC test suite can be included:
     CONFIG_FS_ROMFS=y           : ROMFS support is needed
     CONFIG_EXAMPLES_BASTEST=y   : Enables the BASIC test setup
     CONFIG_EXAMPLES_BASTEST_DEVMINOR=0
     CONFIG_EXAMPLES_BASTEST_DEVPATH="/dev/ram0"

  Usage
  -----
  This setup will initialize the BASIC test (optional):  This will mount
  a ROMFS file system at /mnt/romfs that contains the BASIC test files:

  nsh> bastest
  Registering romdisk at /dev/ram0
  Mounting ROMFS filesystem at target=/mnt/romfs with source=/dev/ram0
  nsh>

  These steps will create and mount a RAMDISK at /tmp (required only for a
  few BASIC commands).  This will create a RAMDISK device at /dev/ram1 with
  size = 512 * 64 = 32KiB and mount it at /tmp:

  nsh> mkrd -m 1 -s 512 64
  nsh> mkfatfs /dev/ram1
  nsh> mount -t vfat /dev/ram1 /tmp
  nsh>

  The interactive interpreter is started like:

  nsh> bas
  bas 2.4
  Copyright 1999-2014 Michael Haardt.
  This is free software with ABSOLUTELY NO WARRANTY.
  >

  Ctrl-D exits the interpreter.

  The test programs can be ran like this:

  nsh> bastest
  Registering romdisk at /dev/ram0
  Mounting ROMFS filesystem at target=/mnt/romfs with source=/dev/ram0
  nsh> bas /mnt/romfs/test01.bas
   1
  hello
   0.0002
   0.0000020
   0.0000002

  nsh>

  Or you can load a test into memory and execute it interactively:

  nsh> bas
  bas 2.4
  Copyright 1999-2014 Michael Haardt.
  This is free software with ABSOLUTELY NO WARRANTY.
  > load "/mnt/romfs/test01.bas"
  > run
   1
  hello
   0.0002
   0.0000020
   0.0000002
  >

Testing LLVM LIBC++ with NuttX
==============================

You can use LLVM LIBC++ on NuttX to get a C++ compiler with C++11 features.
Follow these steps to get it working:

Clone the needed repositories:

    $ git clone https://www.bitbucket.org/acassis/libcxx

    $ git clone https://www.bitbucket.org/nuttx/apps

    $ git clone https://www.bitbucket.org/nuttx/nuttx

Install the libcxx files on NuttX:

    $ cd libcxx

    $ ./install.sh ../nuttx
    Installing LLVM/libcxx in the NuttX source tree
    Installation suceeded

Enter inside NuttX and compile it:

    $ cd ../nuttx

    $ tools/configure.sh stm32f4discovery:testlibcxx
      Copy files
      Refreshing...

    $ ls -l nuttx.bin
    -rwxrwxr-x 1 alan alan 58112 Ago  8 11:08 nuttx.bin

Plug the MiniUSB cable in the STM32F4Discovery board and flash the firmware:

    $ sudo openocd -f interface/stlink-v2.cfg -f target/stm32f4x.cfg -c init \
    -c "reset halt" -c "flash write_image erase nuttx.bin 0x08000000"

    ...

    Info : device id = 0x10036413
    Info : flash size = 1024kbytes
    target halted due to breakpoint, current mode: Thread
    xPSR: 0x61000000 pc: 0x20000046 msp: 0x20001d60
    wrote 65536 bytes from file nuttx.bin in 2.959432s (21.626 KiB/s)

Connect the USB/Serial 3.3V dongle to PA2(board TX) and PA3(board RX) use
minicom or other serial console configured to 115200 8n1.

Press Reset pin of the board and you will see:

    NuttShell (NSH)
    nsh> ?
    help usage:  help [-v] [<cmd>]

      [           cmp         free        mh          sh          usleep
      ?           dirname     help        mv          sleep       xd
      basename    dd          hexdump     mw          test
      break       echo        kill        pwd         time
      cat         exec        ls          rm          true
      cd          exit        mb          rmdir       uname
      cp          false       mkdir       set         unset

    Builtin Apps:
      helloxx

    nsh>


Just type helloxx:

    nsh> helloxx
    helloxx_main: Saying hello from the dynamically constructed instance
    CHelloWorld::HelloWorld: Hello, World!!
    helloxx_main: Saying hello from the instance constructed on the stack
    CHelloWorld::HelloWorld: Hello, World!!
    helloxx_main: Saying hello from the statically constructed instance
    CHelloWorld::HelloWorld: Hello, World!!

    nsh>

Configurations
==============

Common Information
------------------

Each STM32F4Discovery configuration is maintained in a sub-directory and
can be selected as follow:

    tools/configure.sh STM32F4Discovery:<subdir>

Where <subdir> is one of the sub-directories listed in the next paragraph

  NOTES (common for all configurations):

  1. This configuration uses the mconf-based configuration tool.  To
     change this configuration using that tool, you should:

     a. Build and install the kconfig-mconf tool.  See nuttx/README.txt
        see additional README.txt files in the NuttX tools repository.

     b. Execute 'make menuconfig' in nuttx/ in order to start the
        reconfiguration process.

Configuration Sub-directories
-------------------------

  audio:
  -----

  This configuration is a variant of the NSH configuration used for
  demonstrating PCM audio using the CS43L22 stereo DAC/amplifier on board
  the STM32F4 Discovery and the STM32 I2S DMA interface.  It uses the
  file player at apps/system/nxplayer.  The serial console is on USART2.

  The original CS43L22 and STM32 I2S drivers were contribued by Taras
  Drozdovsky in May of 2017.  The audio configuration was contributed by
  Alan Carvalho de Assis and derives, in part, from the work of Taras at
  https://github.com/tdrozdovskiy/CS43L22-Audio-driver.

  Usage instructions from the README file at the location:

  1. Prepare USB flash storage.  This configuration depends on .WAV files
     provided to the system via a USB flash stick.  There are some sample
     audio files at https://github.com/tdrozdovskiy/CS43L22-Audio-driver
     and these steps will put those sample .WAV files onto the USB flash:

     a. Format the USB flash storage into FAT. For example by next command

       $ mkfs.vfat /dev/sdb1

     b. Create folder /music

       $ mkdir music

     c. Copy files from /audio_samples/ to /music folder of USB flash storage

      $ cp <repo>/audio_samples/* /mnt/media/music/

     You should be able to use either Taras' .wav files like that or, if
     you like, your own compatible .wav files.

  2. Example usage CS43L22 Audio driver

    a. Power On or reset the STM32F4 Discovery board.  We can see the Nuttx
       command line prompt:

      NuttShell (NSH)
      nsh>

    b. Mount the usb flash device into our file system

      nsh> mount -t vfat /dev/sda/ /mnt/sda

    c. Start the NxPlayer program and Enter the help command to view the list
       of commands

      nsh> nxplayer
      NxPlayer version 1.04
      h for commands, q to exit
      nxplayer> h
      NxPlayer commands
      ================
        balance d%      : Set balance percentage (< 50% means more left)
        device devfile  : Specify a preferred audio device
        h               : Display help for commands
        help            : Display help for commands
        mediadir path   : Change the media directory
        play filename   : Play a media file
        pause           : Pause playback
        resume          : Resume playback
        stop            : Stop playback
        tone freq secs  : Produce a pure tone
        q               : Exit NxPlayer
        quit            : Exit NxPlayer
        volume d%       : Set volume to level specified

    d. Play the test sample track (cu44k.wav - 44100Hz, 16bit, stereo).

      nxplayer> play cu44k.wav

    e. Set the volume value to 50%.

      nxplayer> volume 50

    f. Stop the current track and play another one

      nxplayer> stop
      nxplayer> play hn.wav

  cxxtest:
  -------

  The C++ standard libary test at apps/testing/cxxtest configuration.  This
  test is used to verify the uClibc++ port to NuttX.  This configuration may
  be selected as follows:

    tools/configure.sh sim:cxxtest

  NOTES:

  1. Before you can use this example, you must first install the uClibc++
     C++ library.  This is located outside of the NuttX source tree in the
     NuttX uClibc++ GIT repository.  See the README.txt file there for
     instructions on how to install uClibc++

  2. Ideally, you should build with a toolchain based on GLIBC or
     uClibc++.  It you use a toolchain based on newlib, you may see
     an error like the following:

     .../lib/libsupc++.a(vterminate.o): In function `__gnu_cxx::__verbose_terminate_handler()':
     vterminate.cc:(....): undefined reference to `_impure_ptr'

     Here is a quick'n'dirty fix:

     1. Get the directory where you can find libsupc++:

        arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -print-file-name=libsupc++.a

     2. Go to that directory and save a copy of vterminate.o (in case you
        want to restore it later:

        cd <the-directory-containing-libsupc++.a>
        arm-none-eabi-ar.exe -x libsupc++.a vterminate.o

     3. Then remove vterminate.o from the library.  At build time, the
        uClibc++ package will provide a usable replacement vterminate.o.

     Steps 2 and 3 will require root privileges on most systems (not Cygwin).

     Now NuttX should link with no problem.  If you want to restore the
     vterminate.o that you removed from libsupc++, you can do that with:

       arm-none-eabi-ar.exe rcs libsupc++.a vterminate.o

  3. Exceptions are enabled and workking (CONFIG_UCLIBCXX_EXCEPTION=y)

  elf:
  ---

    This configuration uses apps/examples/elf in order to test the ELF
    loader.

    NOTES:

    1. Default platform/toolchain:

       CONFIG_HOST_WINDOWS=y                   : Windows
       CONFIG_WINDOWS_CYGWIN=y                 : Cygwin environment on Windows
       CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery under Windows

    2. By default, this project assumes that you are *NOT* using the DFU
       bootloader.

    3. It appears that you cannot execute from CCM RAM.  This is why the
       following definition appears in the defconfig file:

       CONFIG_STM32_CCMEXCLUDE=y

    4. This configuration requires that you have the genromfs tool installed
       on your system and that you have the full path to the installed genromfs
       executable in PATH variable (see apps/examples/README.txt)

    5. This configuration can be extended to use the hello++4 example and to
       build uClibc with the following additions to to the configuration file
       (from Leo aloe3132):

       CONFIG_C99_BOOL8=y
       CONFIG_HAVE_CXXINITIALIZE=y

       CONFIG_UCLIBCXX=y
       CONFIG_UCLIBCXX_EXCEPTION=y
       CONFIG_UCLIBCXX_HAVE_LIBSUPCXX=y
       CONFIG_UCLIBCXX_IOSTREAM_BUFSIZE=32

       CONFIG_EXAMPLES_ELF_CXXINITIALIZE=y
       CONFIG_EXAMPLES_ELF_UCLIBCXX=y

    6. By default, this configuration uses the ROMFS file system.  It can also
       be modified to use the compressed CROMFS:

       -CONFIG_PATH_INITIAL="/mnt/romfs"
       +CONFIG_PATH_INITIAL="/mnt/cromfs"

       -CONFIG_FS_ROMFS=y
       +CONFIG_FS_CROMFS=y

       -CONFIG_EXAMPLES_ELF_ROMFS=y
       +CONFIG_EXAMPLES_ELF_CROMFS=y

    7. The network initialization thread is enabled in this configuration.
       As a result, networking initialization is performed asynchronously with
       NSH bring-up.

       The network monitor is not enabled in this configuration, however, so
       the firmware will not know when the network is disconnected or
       reconnected.  The NSH Network Monitor cannot be used with the
       STM32F4DIS-BB base board because the LAN8720 is configured in REF_CLK
       OUT mode.  In that mode, the PHY interrupt is not supported.  The NINT
       pin serves as REFLCK0 in that case.

  hciuart:
  -------

    This configuration was used for test the HCI UART driver.  The HCI UART
    is enabled on USART3 as well as the test application at
    apps/wireless/bluetoot/btsak.

    NOTES:

    1. This configuration assumes that that you are using the STM32F4DIS-BB
       base board with serial console on USART6.  If you are not using the
       STM32F4DIS-BB, then you will want to disable support for the base
       board.

         -CONFIG_STM32F4DISBB=y
         +# CONFIG_STM32F4DISBB is not set

       You may also want to reconfigure the serial console to USART1.

    2. The HCI UART is assume to connect to the UART3 on the following pins:

         USART3 TX :  PB10
         USART3 RX :  PB11
         USART3 CTS:  PB13
         USART3 RTS:  PB14

       The HCI UART selection can be changed by re-configuring and assigning
       the different U[S]ART to the HCI.  The U[S]ART pin selections can be
       changed by modifying the disambiguation definitions in
       boards/stm32f4discovery/include/board.h

       I have been testing with the DVK_BT960_SA board via J10 as follows:

         DVK_BT860-SA J10     STM32F4 Discovery P1
         pin 1  GND                             P1 pin 49
         pin 2  Module_RTS_O  USART3_CTS PB13,  P1 pin 37
         pin 3  N/C
         pin 4  Module_RX_I   USART3_TXD PB10,  P1 pin 34
         pin 5  Module_TX_O   USART3_RX  PB11,  P1 pin 35
         pin 6  Module_CTS_I  USART3_RTS PB14,  P1 pin 38

       NOTICE that the BT860 uses BT860-centric naming, the Rx pin is for
       BT860 receive and needs to connect with the STM32 Tx pin, the Tx pin
       is for BT860 transmit an needs to be connected with the STM32 Rx pin,
       etc.  Other parts may use host-centric naming so that the HCI UART Rx
       pin connects to the STM32 Rx pin, Tx to Tx pin, etc.

    3. Due to conflicts, USART3 many not be used if Ethernet is enabled with
       the STM32F4DIS-BB base board:

         PB-11 conflicts with Ethernet TXEN
         PB-13 conflicts with Ethernet TXD1

       If you need to use the HCI uart with Ethernet, then you will need to
       configure a new U[S]ART and/or modify the pin selections in
       include/board.h.

    4. Stack sizes are large and non-optimal.  Don't judge memory usage
       without tuning.

    5. I tested using the Laird DVK_BT860.  The BT860 defaults to 115200
       BAUD but is capable of transfers up to 4M.  The documentation says
       that the part supports auto baudrate detection, but I have found no
       documentation on how to use that.

       Currently the "generic" HCI UART upper half is used with the BT860
       and that upper half driver supports only a fixed (but configurable
       BAUD) is used and this must be set to the BT860 default (115200).

       A custom BT860 upper half driver is needed that can use vendor
       specific command:  Baud rate can be set with such a vendor-specific
       command.  Ideally, the sequence would be:  (1) start at default baud
       rate, (2) get local version info, (3) send the vendor-specific baud
       rate change command, (4) wait for response, and (5) set the local
       UART to the matching, higher baud rate.

       The custom, vendor-specific BT860 command is:

         {0x18, 0xfc, 0x06, 0x00, 0x00, NN, NN, NN, NN}

       where {NN, NN, NN, NN} is the requested baud in little endian byte order.

       If an initialization script is used then (5) then send initialization
       scripts script.  After sending the last command from the
       initialization script, (6) reset the local UART.  Finally, (7) send
       vendor-specific baud rate change command, (8) wait for response, and
       (9) set local UART to high baud rate.

       The command to write the initialization script into NVRAM is another
       story for another time and another place.

       If you use a different HCI UART, you will need to modify this setting:

         CONFIG_BLUETOOTH_UART_GENERIC=y

       and you may have to add some support in drivers/wireless/bluetooth.

  ipv6:
  ----
    This is another version of the NuttShell configuration for the
    STM32F4-Discovery with the STM32F4DIS-BB base board.  It is very similar
    to the netnsh configuration except that it has IPv6 enabled and IPv4
    disabled.  Several network utilities that are not yet available when
    IPv6 is disabled.

    NOTES:

    1. As of 2015-02-05, this configuration was identical to the netnsh
       configuration other than using IPv6.  So all of the notes above
       regarding the netnsh configuration apply.

       a. Telnet does work with IPv6 but is not enabled in this
          configuration (but could be).
       b. The network initialization thread was enabed in the netnsh
          configuration on 2015-09-28, but not in the ipv6 configuration.

    2. This configuration can be modified to that both IPv4 and IPv6
       are support.  Here is a summary of the additional configuration
       settings required to support both IPv4 and IPv6:

         CONFIG_NET_IPv4=y
         CONFIG_NET_ARP=y
         CONFIG_NET_ARP_SEND=y (optional)
         CONFIG_NET_ICMP=y
         CONFIG_NET_ICMP_SOCKET=y

         CONFIG_NETDB_DNSCLIENT=y
         CONFIG_NETUTILS_TELNETD=y

         CONFIG_NSH_IPADDR=0x0a000002
         CONFIG_NSH_DRIPADDR=0x0a000001
         CONFIG_NSH_NETMASK=0xffffff00
         CONFIG_NSH_TELNET=y

       Then from NSH, you have both ping and ping6 commands:

         nsh> ping 10.0.0.1
         nsh> ping6 fc00::1

       And from the host you can do similar:

         ping 10.0.0.2
         ping6 fc00::2   (Linux)
         ping -6 fc00::2 (Windows cmd)

       and Telnet is now enabled and works from the host... but only using
       IPv6 addressing:

         telnet fc00::2

       That is because the Telnet daemon will default to IPv6 and there is
       no Telnet option to let you select which if both IPv4 and IPv6 are
       enabled.

    3. I have used this configuration to serve up IP address prefixes
       in a local network with these modifications to the configuration:

       +CONFIG_NET_ICMPv6_ROUTER=y
       +CONFIG_NET_ICMPv6_PREFLEN=64
       +CONFIG_NET_ICMPv6_PREFIX_1=0xfc00
       +CONFIG_NET_ICMPv6_PREFIX_2=0x0000
       +CONFIG_NET_ICMPv6_PREFIX_3=0x0000
       +CONFIG_NET_ICMPv6_PREFIX_4=0x0000
       +CONFIG_NET_ICMPv6_PREFIX_5=0x0000
       +CONFIG_NET_ICMPv6_PREFIX_6=0x0000
       +CONFIG_NET_ICMPv6_PREFIX_7=0x0000
       +CONFIG_NET_ICMPv6_PREFIX_8=0x0000

       +CONFIG_NSH_IPv6NETMASK_5=0x0000
       -CONFIG_NSH_IPv6NETMASK_5=0xffff

       +CONFIG_NSH_IPv6NETMASK_6=0x0000
       -CONFIG_NSH_IPv6NETMASK_6=0xffff

       +CONFIG_NSH_IPv6NETMASK_7=0x0000
       -CONFIG_NSH_IPv6NETMASK_7=0xffff

       +CONFIG_NSH_IPv6NETMASK_8=0x0000
       -CONFIG_NSH_IPv6NETMASK_8=0xff80

  kostest:
  -------
    This is identical to the ostest configuration below except that NuttX
    is built as a kernel-mode, monolithic module and the user applications
    are built separately.  Is is recommended to use a special make command;
    not just 'make' but make with the following two arguments:

        make pass1 pass2

    In the normal case (just 'make'), make will attempt to build both user-
    and kernel-mode blobs more or less interleaved.  This actual works!
    However, for me it is very confusing so I prefer the above make command:
    Make the user-space binaries first (pass1), then make the kernel-space
    binaries (pass2)

    NOTES:

    1. This is the default platform/toolchain in the configuration:

       CONFIG_HOST_WINDOWS=y                   : Windows
       CONFIG_WINDOWS_CYGWIN=y                 : Cygwin environment on Windows
       CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery under Windows

       This is easily changed by modifying the configuration.

    2. At the end of the build, there will be several files in the top-level
       NuttX build directory:

       PASS1:
         nuttx_user.elf    - The pass1 user-space ELF file
         nuttx_user.hex    - The pass1 Intel HEX format file (selected in defconfig)
         User.map          - Symbols in the user-space ELF file

       PASS2:
         nuttx             - The pass2 kernel-space ELF file
         nuttx.hex         - The pass2 Intel HEX file (selected in defconfig)
         System.map        - Symbols in the kernel-space ELF file

    3. Combining .hex files.  If you plan to use the STM32 ST-Link Utility to
       load the .hex files into FLASH, then you need to combine the two hex
       files into a single .hex file.  Here is how you can do that.

       a. The 'tail' of the nuttx.hex file should look something like this
          (with my comments added):

            $ tail nuttx.hex
            # 00, data records
            ...
            :10 9DC0 00 01000000000800006400020100001F0004
            :10 9DD0 00 3B005A0078009700B500D400F300110151
            :08 9DE0 00 30014E016D0100008D
            # 05, Start Linear Address Record
            :04 0000 05 0800 0419 D2
            # 01, End Of File record
            :00 0000 01 FF

          Use an editor such as vi to remove the 05 and 01 records.

       b. The 'head' of the nuttx_user.hex file should look something like
          this (again with my comments added):

            $ head nuttx_user.hex
            # 04, Extended Linear Address Record
            :02 0000 04 0801 F1
            # 00, data records
            :10 8000 00 BD89 01084C800108C8110208D01102087E
            :10 8010 00 0010 00201C1000201C1000203C16002026
            :10 8020 00 4D80 01085D80010869800108ED83010829
            ...

          Nothing needs to be done here.  The nuttx_user.hex file should
          be fine.

       c. Combine the edited nuttx.hex and un-edited nuttx_user.hex
          file to produce a single combined hex file:

          $ cat nuttx.hex nuttx_user.hex >combined.hex

       Then use the combined.hex file with the STM32 ST-Link tool.  If
       you do this a lot, you will probably want to invest a little time
       to develop a tool to automate these steps.

  module:
  ------

    A simple stripped down NSH configuration that was used for testing NuttX
    OS modules using the test at apps/examples/module.  Key difference from
    other NSH configurations include these additions to the configuration file:

      CONFIG_BOARDCTL_OS_SYMTAB=y
      CONFIG_EXAMPLES_MODULE=y
      CONFIG_EXAMPLES_MODULE_BUILTINFS=y
      CONFIG_EXAMPLES_MODULE_DEVMINOR=0
      CONFIG_EXAMPLES_MODULE_DEVPATH="/dev/ram0"
      CONFIG_FS_ROMFS=y
      CONFIG_LIBC_ARCH_ELF=y
      CONFIG_MODULE=y
      CONFIG_LIBC_MODLIB=y
      CONFIG_MODLIB_MAXDEPEND=2
      CONFIG_MODLIB_ALIGN_LOG2=2
      CONFIG_MODLIB_BUFFERSIZE=128
      CONFIG_MODLIB_BUFFERINCR=32

     The could be followed may be added for testing shared libraries in the
     FLAT build using apps/examples/sotest (assuming that you also have SD
     card support enabled and that the SD card is mount at /mnt/sdcard):

      CONFIG_LIBC_DLFCN=y
      CONFIG_EXAMPLES_SOTEST=y
      CONFIG_EXAMPLES_SOTEST_BINDIR="/mnt/sdcard"

    NOTE: You must always have:

      CONFIG_STM32_CCMEXCLUDE=y

    because code cannot be executed from CCM memory.

    STATUS:
    2018-06-02: Configuration added by Alan Carvalho de Assis.

  netnsh:
  ------
    This is a special version of the NuttShell (nsh) configuration that is
    tailored to work with the STM32F4DIS-BB base board.  This version
    derives from nsh configuration so all of the notes apply there except as
    noted below.

    NOTES:

    1. This example uses USART6 for the serial console.  The STM32F4DIS-BB
       provides RS-232 drivers for USART6 and allows access via the DB9
       connector on the base board.  USART6 is, therefore, the more
       convenient UART to use for the serial console.

    2. Networking is enabled.  The STM32F4DIS-BB has an SMC LAN2870 PHY
       and RJ5 network connector.  Support is enabled for ICMP, TCP/IP,
       UDP, and ARP.

    3. SD card support is enabled.  The STM32F4DIS-BB has an on-board
       microSD slot that should be automatically registered as the block
       device /dev/mmcsd0 when an SD card is present.  The SD card can
       then be mounted by the NSH command:

       nsh> mount -t /dev/mmcsd0 /mnt/sdcard

    4. CCM memory is not included in the heap in this configuration.  That
       is because the SD card uses DMA and if DMA memory is allocated from
       the CCM memory, the DMA will failure.  This is an STM32 hardware
       limitation.

       If you want to get the CCM memory back in the heap, then you can

         a) Disable microSD support (and DMAC2 which is then no longer
            needed).  If you reduce the clocking by a huge amount, it might
            be possible to use microSD without DMA.  This, however, may
            not be possible.
         b) Develop a strategy to manage CCM memory and DMA memory.  Look
            at this discussion on the NuttX Wiki:
            http://www.nuttx.org/doku.php?id=wiki:howtos:stm32-ccm-alloc

       To put the CCM memory back into the heap you would need to change
       the following in the NuttX configuration:

         CONFIG_STM32_CCMEXCLUDE=n  : Don't exclude CCM memory from the heap
         CONFIG_MM_REGIONS=2        : With CCM, there will be two memory regions

  nsh:
  ---
    Configures the NuttShell (nsh) located at apps/examples/nsh.  The
    Configuration enables the serial interfaces on USART2.  Support for
    builtin applications is enabled, but in the base configuration no
    builtin applications are selected (see NOTES below).

    NOTES:

    1. By default, this configuration uses the CodeSourcery toolchain
       for Windows and builds under Cygwin (or probably MSYS).  That
       can easily be reconfigured, of course.

       CONFIG_HOST_WINDOWS=y                   : Builds under Windows
       CONFIG_WINDOWS_CYGWIN=y                 : Using Cygwin
       CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery for Windows

    2. To use this configuration with the STM32F4DIS-BB baseboard you
       should:

       - Select the STM32F4DIS-BB baseboard in the board configuration
         menu
       - Disable USART2 and select USART6 in the STM32 peripheral selection
         menu
       - Select USART6 as the serial console at 115200 8N1 in the
         Drivers menus

    3. This example supports the PWM test (apps/examples/pwm) but this must
       be manually enabled by selecting:

       CONFIG_PWM=y              : Enable the generic PWM infrastructure
       CONFIG_STM32_TIM4=y       : Enable TIM4
       CONFIG_STM32_TIM4_PWM=y   : Use TIM4 to generate PWM output

       See also apps/examples/README.txt

       Special PWM-only debug options:

       CONFIG_DEBUG_PWM_INFO

    4. This example supports the Quadrature Encode test (apps/examples/qencoder)
       but this must be manually enabled by selecting:

       CONFIG_EXAMPLES_QENCODER=y : Enable the apps/examples/qencoder
       CONFIG_SENSORS=y           : Enable support for sensors
       CONFIG_SENSORS_QENCODER=y          : Enable the generic Quadrature Encoder infrastructure
       CONFIG_STM32_TIM8=y        : Enable TIM8
       CONFIG_STM32_TIM2=n        : (Or optionally TIM2)
       CONFIG_STM32_TIM8_QE=y     : Use TIM8 as the quadrature encoder
       CONFIG_STM32_TIM2_QE=y     : (Or optionally TIM2)

       See also apps/examples/README.tx. Special debug options:

       CONFIG_DEBUG_SENSORS

    5. This example supports the watchdog timer test (apps/examples/watchdog)
       but this must be manually enabled by selecting:

       CONFIG_EXAMPLES_WATCHDOG=y : Enable the apps/examples/watchdog
       CONFIG_WATCHDOG=y          : Enables watchdog timer driver support
       CONFIG_STM32_WWDG=y        : Enables the WWDG timer facility, OR
       CONFIG_STM32_IWDG=y        : Enables the IWDG timer facility (but not both)

       The WWDG watchdog is driven off the (fast) 42MHz PCLK1 and, as result,
       has a maximum timeout value of 49 milliseconds.  for WWDG watchdog, you
       should also add the fillowing to the configuration file:

       CONFIG_EXAMPLES_WATCHDOG_PINGDELAY=20
       CONFIG_EXAMPLES_WATCHDOG_TIMEOUT=49

       The IWDG timer has a range of about 35 seconds and should not be an issue.

     6. USB Support (CDC/ACM device)

        CONFIG_STM32_OTGFS=y          : STM32 OTG FS support
        CONFIG_USBDEV=y               : USB device support must be enabled
        CONFIG_CDCACM=y               : The CDC/ACM driver must be built
        CONFIG_NSH_BUILTIN_APPS=y     : NSH built-in application support must be enabled
        CONFIG_NSH_ARCHINIT=y         : To perform USB initialization

     7. Using the USB console.

        The STM32F4Discovery NSH configuration can be set up to use a USB CDC/ACM
        (or PL2303) USB console.  The normal way that you would configure the
        the USB console would be to change the .config file like this:

        CONFIG_STM32_OTGFS=y           : STM32 OTG FS support
        CONFIG_USART2_SERIAL_CONSOLE=n : Disable the USART2 console
        CONFIG_DEV_CONSOLE=n           : Inhibit use of /dev/console by other logic
        CONFIG_USBDEV=y                : USB device support must be enabled
        CONFIG_CDCACM=y                : The CDC/ACM driver must be built
        CONFIG_CDCACM_CONSOLE=y        : Enable the CDC/ACM USB console.

        NOTE: When you first start the USB console, you have hit ENTER a few
        times before NSH starts.  The logic does this to prevent sending USB data
        before there is anything on the host side listening for USB serial input.

    8.  Here is an alternative USB console configuration.  The following
        configuration will also create a NSH USB console but this version
        will use /dev/console.  Instead, it will use the normal /dev/ttyACM0
        USB serial device for the console:

        CONFIG_STM32_OTGFS=y           : STM32 OTG FS support
        CONFIG_USART2_SERIAL_CONSOLE=y : Keep the USART2 console
        CONFIG_DEV_CONSOLE=y           : /dev/console exists (but NSH won't use it)
        CONFIG_USBDEV=y                : USB device support must be enabled
        CONFIG_CDCACM=y                : The CDC/ACM driver must be built
        CONFIG_CDCACM_CONSOLE=n        : Don't use the CDC/ACM USB console.
        CONFIG_NSH_USBCONSOLE=y        : Instead use some other USB device for the console

        The particular USB device that is used is:

        CONFIG_NSH_USBCONDEV="/dev/ttyACM0"

        The advantage of this configuration is only that it is easier to
        bet working.  This alternative does has some side effects:

        - When any other device other than /dev/console is used for a user
          interface, linefeeds (\n) will not be expanded to carriage return /
          linefeeds (\r\n).  You will need to set your terminal program to account
          for this.

        - /dev/console still exists and still refers to the serial port. So
          you can still use certain kinds of debug output (see include/debug.h, all
          of the debug output from interrupt handlers will be lost.

        - But don't enable USB debug output!  Since USB is console is used for
          USB debug output and you are using a USB console, there will be
          infinite loops and deadlocks:  Debug output generates USB debug
          output which generatates USB debug output, etc.  If you want USB
          debug output, you should consider enabling USB trace
          (CONFIG_USBDEV_TRACE) and perhaps the USB monitor (CONFIG_USBMONITOR).

          See the usbnsh configuration below for more information on configuring
          USB trace output and the USB monitor.

    9. USB OTG FS Host Support.  The following changes will enable support for
       a USB host on the STM32F4Discovery, including support for a mass storage
       class driver:

       Device Drivers ->
         CONFIG_USBDEV=n          : Make sure tht USB device support is disabled
         CONFIG_USBHOST=y         : Enable USB host support
         CONFIG_USBHOST_ISOC_DISABLE=y

       Device Drivers -> USB Host Driver Support
         CONFIG_USBHOST_MSC=y     : Enable the mass storage class

       System Type -> STM32 Peripheral Support
         CONFIG_STM32_OTGFS=y     : Enable the STM32 USB OTG FS block
         CONFIG_STM32_SYSCFG=y    : Needed for all USB OTF FS support

       RTOS Features -> Work Queue Support
         CONFIG_SCHED_WORKQUEUE=y : High priority worker thread support is required
         CONFIG_SCHED_HPWORK=y    :   for the mass storage class driver.

       File Systems ->
         CONFIG_FS_FAT=y          : Needed by the USB host mass storage class.

       Board Selection ->
         CONFIG_LIB_BOARDCTL=y    : Needed for CONFIG_NSH_ARCHINIT

       Application Configuration -> NSH Library
         CONFIG_NSH_ARCHINIT=y    : Architecture specific USB initialization
                                  : is needed for NSH

       With those changes, you can use NSH with a FLASH pen driver as shown
       belong.  Here NSH is started with nothing in the USB host slot:

       NuttShell (NSH) NuttX-x.yy
       nsh> ls /dev
       /dev:
        console
        null
        ttyS0

       After inserting the FLASH drive, the /dev/sda appears and can be
       mounted like this:

       nsh> ls /dev
       /dev:
        console
        null
        sda
        ttyS0
       nsh> mount -t vfat /dev/sda /mnt/stuff
       nsh> ls /mnt/stuff
       /mnt/stuff:
        -rw-rw-rw-   16236 filea.c

       And files on the FLASH can be manipulated to standard interfaces:

       nsh> echo "This is a test" >/mnt/stuff/atest.txt
       nsh> ls /mnt/stuff
       /mnt/stuff:
        -rw-rw-rw-   16236 filea.c
        -rw-rw-rw-      16 atest.txt
       nsh> cat /mnt/stuff/atest.txt
       This is a test
       nsh> cp /mnt/stuff/filea.c fileb.c
       nsh> ls /mnt/stuff
       /mnt/stuff:
        -rw-rw-rw-   16236 filea.c
        -rw-rw-rw-      16 atest.txt
        -rw-rw-rw-   16236 fileb.c

       To prevent data loss, don't forget to un-mount the FLASH drive
       before removing it:

       nsh> umount /mnt/stuff

   10. I used this configuration to test the USB hub class.  I did this
       testing with the following changes to the configuration (in addition
       to those listed above for base USB host/mass storage class support):

       Drivers -> USB Host Driver Support
         CONFIG_USBHOST_HUB=y     : Enable the hub class
         CONFIG_USBHOST_ASYNCH=y  : Asynchonous I/O supported needed for hubs

       System Type -> USB host configuration
         To be determined

       Board Selection ->
         CONFIG_STM32F4DISCO_USBHOST_STACKSIZE=2048 (bigger than it needs to be)

       RTOS Features -> Work Queue Support
         CONFIG_SCHED_LPWORK=y     : Low priority queue support is needed
         CONFIG_SCHED_LPNTHREADS=1
         CONFIG_SCHED_LPWORKSTACKSIZE=1024

       NOTES:

       1. It is necessary to perform work on the low-priority work queue
          (vs. the high priority work queue) because deferred hub-related
          work requires some delays and waiting that is not appropriate on
          the high priority work queue.

       2. Stack usage make increase when USB hub support is enabled because
          the nesting depth of certain USB host class logic can increase.

       STATUS:
       2015-04-30
          Appears to be fully functional.

   11. Using USB Device as a Mass Storage for the host computer:

       System Type  --->
           STM32 Peripheral Support  --->
               [*] OTG FS

       Device Drivers  --->
           [*] USB Device Driver Support  --->
               [*]   USB Mass storage class device  --->
                   [*]   Mass storage removable

           [*] RAM Disk Support

       Board Selection  --->
           [*] Enable boardctl() interface
           [*]   Enable USB device controls

       File Systems  --->
           [*] FAT file system
           [*]   FAT upper/lower names
           [*]   FAT long file names

           [*] PROCFS File System

       Application Configuration  --->
           System Libraries and NSH Add-Ons  --->
               [*] USB Mass Storage Device Commands  --->
                   (/dev/ram0) LUN1 Device Path

       Compile and flash the firmware in the board as usual, then in the nsh:

       nsh> mkrd -m 0 -s 512 64

       nsh> ls /dev
       /dev:
        console
        null
        ram0
        ttyS0

       nsh> mkfatfs /dev/ram0

       Connect a USB cable to STM32F4Discovery board (connector CN5) and run:

       nsh> msconn
       mcsonn_main: Creating block drivers
       mcsonn_main: Configuring with NLUNS=1
       mcsonn_main: handle=1000a550
       mcsonn_main: Bind LUN=0 to /dev/ram0
       mcsonn_main: Connected

       In this moment a 33KB disk should appear in your host computer. If you
       saved some file on this small disk you can now run disconnect command:

       nsh> msdis
       msdis: Disconnected

       Remove the USB cable from microUSB connector and run:

       nsh> mount -t vfat /dev/ram0 /mnt

       nsh> ls /mnt
       /mnt:
        TEST.TXT

       nsh> cat /mnt/TEST.TXT
       Testing

  nxlines:
  ------
    An example using the NuttX graphics system (NX).   This example focuses on
    placing lines on the background in various orientations.

      CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery under Windows
      CONFIG_LCD_LANDSCAPE=y                  : 320x240 landscape orientation

    The STM32F4Discovery board does not have any graphics capability.  This
    configuration assumes that you have connected an SD1289-based LCD as
    described above under "SSD1289".  NOTE:  At present, it has not been
    proven that the STM32F4Discovery can actually drive an LCD.  There are
    some issues with how some of the dedicated FSMC pins are used on the
    boards.  This configuration may not be useful and may only serve as
    an illustration of how to build for th SSD1289 LCD.

  NOTES:

  1. As of this writing, I have not seen the LCD work!

  2. This configured can be re-configured to use either the
     UG-2864AMBAG01 or UG-2864HSWEG01 0.96 inch OLEDs by adding
     or changing the following items in the configuration (using
     'make menuconfig'):

     +CONFIG_SPI_CMDDATA=y

     -CONFIG_LCD_MAXCONTRAST=1
     -CONFIG_LCD_MAXPOWER=255
     +CONFIG_LCD_MAXCONTRAST=255
     +CONFIG_LCD_MAXPOWER=1

     -CONFIG_LCD_SSD1289=y
     -CONFIG_SSD1289_PROFILE1=y
     +CONFIG_LCD_UG2864AMBAG01=y              : For the UG-2964AMBAG01
     +CONFIG_UG2864AMBAG01_SPIMODE=3
     +CONFIG_UG2864AMBAG01_FREQUENCY=3500000
     +CONFIG_UG2864AMBAG01_NINTERFACES=1

     -CONFIG_NX_DISABLE_1BPP=y
     +CONFIG_NX_DISABLE_16BPP=y
     +CONFIG_NXSTART_EXTERNINIT=y

     -CONFIG_EXAMPLES_NXLINES_BGCOLOR=0x0320
     -CONFIG_EXAMPLES_NXLINES_LINEWIDTH=16
     -CONFIG_EXAMPLES_NXLINES_LINECOLOR=0xffe0
     -CONFIG_EXAMPLES_NXLINES_BORDERWIDTH=4
     -CONFIG_EXAMPLES_NXLINES_BORDERCOLOR=0xffe0
     -CONFIG_EXAMPLES_NXLINES_CIRCLECOLOR=0xf7bb
     -CONFIG_EXAMPLES_NXLINES_BPP=16
     +CONFIG_EXAMPLES_NXLINES_BGCOLOR=0x00
     +CONFIG_EXAMPLES_NXLINES_LINEWIDTH=4
     +CONFIG_EXAMPLES_NXLINES_LINECOLOR=0x01
     +CONFIG_EXAMPLES_NXLINES_BORDERWIDTH=2
     +CONFIG_EXAMPLES_NXLINES_BORDERCOLOR=0x01
     +CONFIG_EXAMPLES_NXLINES_CIRCLECOLOR=0x00
     +CONFIG_EXAMPLES_NXLINES_BPP=1
     +CONFIG_EXAMPLES_NXLINES_EXTERNINIT=y

     There are some issues with with the presentation... some tuning of the
     configuration could fix that.  Lower resolution displays are also more
     subject to the "fat, flat line bug" that I need to fix someday.  See
     http://www.nuttx.org/doku.php?id=wiki:graphics:nxgraphics for a description
     of the fat, flat line bug.

  pm:
  --
    This is a configuration that is used to test STM32 power management, i.e.,
    to test that the board can go into lower and lower states of power usage
    as a result of inactivity.  This configuration is based on the nsh2
    configuration with modifications for testing power management.  This
    configuration should provide some guidelines for power management in your
    STM32 application.

    NOTES:

    1. Default configuration is Cygwin under windows using the CodeSourcery
       toolchain:

         CONFIG_HOST_WINDOWS=y                   : Windows
         CONFIG_WINDOWS_CYGWIN=y                 : Cygwin
         CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery under Windows

    2. CONFIG_ARCH_CUSTOM_PMINIT and CONFIG_ARCH_IDLE_CUSTOM are necessary
       parts of the PM configuration:

         CONFIG_ARCH_CUSTOM_PMINIT=y

       CONFIG_ARCH_CUSTOM_PMINIT moves the PM initialization from
       arch/arm/src/stm32/stm32_pminitialiaze.c to boards/stm3210-eval/src/stm32_pm.c.
       This allows us to support board-specific PM initialization.

         CONFIG_ARCH_IDLE_CUSTOM=y

       The bulk of the PM activities occur in the IDLE loop.  The IDLE loop
       is special because it is what runs when there is no other task running.
       Therefore when the IDLE executes, we can be assure that nothing else
       is going on; this is the ideal condition for doing reduced power
       management.

       The configuration CONFIG_ARCH_IDLE_CUSTOM allows us to "steal" the
       normal STM32 IDLE loop (of arch/arm/src/stm32/stm32_idle.c) and replace
       this with our own custom IDLE loop (at boards/stm3210-eval/src/up_idle.c).

    3. Here are some additional things to note in the configuration:

        CONFIG_PM_BUTTONS=y

       CONFIG_PM_BUTTONS enables button support for PM testing.  Buttons can
       drive EXTI interrupts and EXTI interrupts can be used to wakeup for
       certain reduced power modes (STOP mode).  The use of the buttons here
       is for PM testing purposes only; buttons would normally be part the
       application code and CONFIG_PM_BUTTONS would not be defined.

         CONFIG_RTC_ALARM=y

       The RTC alarm is used to wake up from STOP mode and to transition to
       STANDBY mode.  This used of the RTC alarm could conflict with other
       uses of the RTC alarm in your application.

  posix_spawn:
  ------------
    This configuration directory, performs a simple test os the posix_spawn
    interface using apps/examples/posix_spawn.

    NOTES:

    1. Default toolchain:

       CONFIG_HOST_WINDOWS=y                   : Builds under windows
       CONFIG_WINDOWS_CYGWIN=y                 : Using Cygwin and
       CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIW=y     : Generic ARM EABI toolchain for Windows

    2. By default, this project assumes that you are *NOT* using the DFU
       bootloader.

  pseudoterm:
  -----------

    This is a configuration to test the Pseudo Terminal support for NuttX.

    To test it you will need two USB/Serial dongles. The first dongle as
    usual will be used to main NSH console port in USART2 (PA2 and PA3) and
    the second dongle you will connect to UART3 (PB10 and PB11).

    In the main NSH console (in USART2) type: "pts_test &". It will create a
    new console in UART3. Just press ENTER and start typing commands on it.

  testlibcxx
  ----------

    This is a configuration for testing lib++.  See the section above entitled
    "Testing LLVM LIBC++ with NuttX" for detailed information about this
    configuration.

  rgbled:
  -------

    Alan Carvalho de Assis has used the STM32F4-Discovery to drive an RGB LED
    using PWM output.  The external RGB connected this way:

     R = TIM1 CH1 on PE9
     G = TIM2 CH2 on PA1
     B = TIM3 CH3 on PB0

    as described about in the section "RGB LED Driver".

    This configuration uses the example at apps/examples/rgbled to drive the
    external RGB LED>

  rndis:
  ------

    This is a board configuration to demonstrate how to use Ethernet-over-USB,
    in this case using the RNDIS protocol. Using it you can get access to your
    board using Telnet or you can use transfer file to it. Both steps will be
    explained below.

    Your board will be get IP address from a DHCP server. If you want to use a
    fixed IP instead using DHCP, you need to disable the DHCP Client and set
    up its IP. For more info watch: www.youtube.com/watch?v=8noH8v7xNgs

    You can access the board's NuttShell just typing in the Linux terminal:

      $ telnet 10.0.0.2

    You should see something like this:

      Trying 10.0.0.2...
      Connected to 10.0.0.2.
      Escape character is '^]'.

      NuttShell (NSH)
      nsh>

    This board configuration has support to RAMDISK because we need a writable
    filesystem to get files from the computer. Then you need to create first a
    RAMDISK and mount it using these steps:

      nsh> mkrd 64
      nsh> mkfatfs /dev/ram0
      nsh> mount -t vfat /dev/ram0 /mnt

    Open a new Linux terminal and start a webserver, Python one embedded:

      $ python -m SimpleHTTPServer

    It will create a webserver serving in the port 8000 and will share files
    in the current directory where it was executed.

    Then in the NuttShell you can run these commands to download a small file:

      nsh> cd /mnt
      nsh> wget http://10.0.0.1:8000/test.txt
      nsh> ls -l
      /mnt:
       -rw-rw-rw-      23 test.txt

    This configuration also supports:

    1. An NFS file system client.  Relevant configuration options:

       CONFIG_NFS=y
       CONFIG_NFS_STATISTICS=y

    2. Loadable ELF modules

       CONFIG_BUILD_LOADABLE=y
       CONFIG_SYMTAB_ORDEREDBYNAME=y
       CONFIG_ELF=y
       CONFIG_EXAMPLES_HELLO=m
       CONFIG_LIBC_EXECFUNCS=y
       CONFIG_NSH_FILE_APPS=y
       CONFIG_SYSTEM_NSH_SYMTAB=y
       CONFIG_SYSTEM_NSH_SYMTAB_ARRAYNAME="g_symtab"
       CONFIG_SYSTEM_NSH_SYMTAB_COUNTNAME="g_nsymbols"

       Further, the configuration assumes that executable files reside on the
       remotely mounted file system:

       CONFIG_LIB_ENVPATH=y
       CONFIG_PATH_INITIAL="/mnt/nfs/bin"

    3 'ping' support

       CONFIG_NET_ICMP_SOCKET=y
       CONFIG_SYSTEM_PING=y

  usbnsh:
  -------

    This is another NSH example.  If differs from other 'nsh' configurations
    in that this configurations uses a USB serial device for console I/O.
    Such a configuration is useful on the stm32f4discovery which has no
    builtin RS-232 drivers.

    NOTES:

    1. By default, this configuration uses the CodeSourcery toolchain
       for Windows and builds under Cygwin (or probably MSYS).  That
       can easily be reconfigured, of course.

       CONFIG_HOST_WINDOWS=y                   : Builds under Windows
       CONFIG_WINDOWS_CYGWIN=y                 : Using Cygwin
       CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery for Windows

    2. This configuration does have USART2 output enabled and set up as
       the system logging device:

       CONFIG_SYSLOG_CHAR=y               : Use a character device for system logging
       CONFIG_SYSLOG_DEVPATH="/dev/ttyS0" : USART2 will be /dev/ttyS0

       However, there is nothing to generate SYLOG output in the default
       configuration so nothing should appear on USART2 unless you enable
       some debug output or enable the USB monitor.

       NOTE:  Using the SYSLOG to get debug output has limitations.  Among
       those are that you cannot get debug output from interrupt handlers.
       So, in particularly, debug output is not a useful way to debug the
       USB device controller driver.  Instead, use the USB monitor with
       USB debug off and USB trace on (see below).

    3. Enabling USB monitor SYSLOG output.  If tracing is enabled, the USB
       device will save encoded trace output in in-memory buffer; if the
       USB monitor is enabled, that trace buffer will be periodically
       emptied and dumped to the system logging device (USART2 in this
       configuration):

       CONFIG_USBDEV_TRACE=y                   : Enable USB trace feature
       CONFIG_USBDEV_TRACE_NRECORDS=128        : Buffer 128 records in memory
       CONFIG_NSH_USBDEV_TRACE=n               : No builtin tracing from NSH
       CONFIG_NSH_ARCHINIT=y                   : Automatically start the USB monitor
       CONFIG_USBMONITOR=y              : Enable the USB monitor daemon
       CONFIG_USBMONITOR_STACKSIZE=2048 : USB monitor daemon stack size
       CONFIG_USBMONITOR_PRIORITY=50    : USB monitor daemon priority
       CONFIG_USBMONITOR_INTERVAL=2     : Dump trace data every 2 seconds

       CONFIG_USBMONITOR_TRACEINIT=y    : Enable TRACE output
       CONFIG_USBMONITOR_TRACECLASS=y
       CONFIG_USBMONITOR_TRACETRANSFERS=y
       CONFIG_USBMONITOR_TRACECONTROLLER=y
       CONFIG_USBMONITOR_TRACEINTERRUPTS=y

    4. By default, this project assumes that you are *NOT* using the DFU
       bootloader.

    Using the Prolifics PL2303 Emulation
    ------------------------------------
    You could also use the non-standard PL2303 serial device instead of
    the standard CDC/ACM serial device by changing:

      CONFIG_CDCACM=n               : Disable the CDC/ACM serial device class
      CONFIG_CDCACM_CONSOLE=n       : The CDC/ACM serial device is NOT the console
      CONFIG_PL2303=y               : The Prolifics PL2303 emulation is enabled
      CONFIG_PL2303_CONSOLE=y       : The PL2303 serial device is the console

  winbuild:
  --------

    This is a version of the apps/example/ostest, but configure to build natively
    in the Windows CMD shell.

    NOTES:

    1. The beginnings of a Windows native build are in place but still not full
       usable as of this writing.  The windows native build logic is currently
       separate and must be started by:

        make -f Makefile.win

      This build:

        - Uses all Windows style paths
        - Uses primarily Windows batch commands from cmd.exe, with
        - A few extensions from GNUWin32 (or MSYS is you prefer)

      In this build, you cannot use a Cygwin or MSYS shell. Rather the build must
      be performed in a Windows console. Here is a better shell than than the
      standard issue, CMD.exe shell:  ConEmu which can be downloaded from:
      http://code.google.com/p/conemu-maximus5/

       CONFIG_HOST_WINDOWS=y                   : Windows
       CONFIG_WINDOWS_NATIVE=y                 : Native Windows environment
       CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery under Windows

      Build Tools.  The build still relies on some Unix-like commands.  I use
      the GNUWin32 tools that can be downloaded from http://gnuwin32.sourceforge.net/.
      The MSYS tools are probably also a option but are likely lower performance
      since they are based on Cygwin 1.3.

      Host Compiler:  I use the MingGW compiler which can be downloaded from
      http://www.mingw.org/.  If you are using GNUWin32, then it is recommended
      the you not install the optional MSYS components as there may be conflicts.