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README.md

README.md

README

This README file describes the port of NuttX to the Starcat Jupiter Nano development board. This board features the Atmel SAMA5D27 microprocessor as a SIP with 128KB on-chip LPDDR2 RAM (part number ATSAMA5D27C-LD1G). See https://www.starcat.io/products/jupiter-nano/ for further information.

This is based the SAMA5D2-XULT README.txt file.

STATUS
Loading Code into SRAM with J-Link hardware debugger
DRAMBOOT, SRAMBOOT
Running NuttX from SDRAM
Buttons and LEDs
Serial Console
Jupiter Nano Configuration Options
Configurations

Status

Most of this document is a partially corrected clone of the SAMA5D2-XULT README.txt and still contains errors and inconsistencies.

Loading Code into SRAM via JTAG

This description assumes that you have a JTAG debugger such as Segger J-Link connected to the Jupiter Nano. These instructions have only been tested with a Segger J-Link. You may have to adapt them for other JTAG debuggers.

There is a mini-JTAG connector on the board, labeled J4 JTAG. You will need a mini-JTAG adapter board and cable.

Start the GDB server
Start GDB
Use the 'target remote localhost:xxxx' command to attach to the GDB server
Do 'mon reset' then 'mon go' to start the internal boot loader (maybe U-Boot).
Let the boot loader run until it completes SDRAM initialization, then do 'mon halt'.
Now you have SDRAM initialized and you use 'load nuttx' to load the ELF file into SDRAM.
Use 'file nuttx' to load symbols
Set the PC to the NuttX entry point 'mon pc 0x20008E20' and start nuttx using 'mon go'.

Loading Code into SRAM from SD Card

You can boot NuttX from an SD Card. You can download an SD Card image or a zip file of the required files from this page:

https://www.starcat.io/starcat-nuttx/

The SD Card has to be FAT formatted, have an AT91Bootstrap binary called boot.bin, a U-Boot binary called u-boot.bin as well as a compiled device tree for the SAMA5D27C-D1G called at91-sama5d27_jupiter_nano.dtb in the dtbs/ folder. You can build these yourself using the tools at

https://github.com/starcat-io/jupiter-nano-tools

The layout should look like this:

BOOT.BIN
uboot.env
nuttx.bin
u-boot.bin
dtbs/
  at91-sama5d27_jupiter_nano.dtb

You only need uboot.env if you want to boot automatically. See the U-Boot documentation for instructions on how to create this file.

Running NuttX from SDRAM

NuttX will be executed from SDRAM, and NuttX binary must reside on SD Card media.

NuttX Configuration

In order to run from SDRAM, NuttX must be built at origin 0x20008000 in SDRAM (skipping over SDRAM memory used by the bootloader). The following configuration option is required:

CONFIG_SAMA5_BOOT_SDRAM=y
CONFIG_BOOT_RUNFROMSDRAM=y

These options tell the NuttX code that it will be booting and running from SDRAM. In this case, the start-logic will do to things: (1) it will not configure the SAMA5D2 clocking. Rather, it will use the clock configuration as set up by the bootloader. And (2) it will not attempt to configure the SDRAM. Since NuttX is already running from SDRAM, it must accept the SDRAM configuration as set up by the bootloader.

Boot sequence

Reference: http://www.at91.com/linux4sam/bin/view/Linux4SAM/GettingStarted

Several pieces of software are involved to boot NuttX into SDRAM. First is the primary bootloader in ROM which is in charge to check if a valid application is present on supported media (NOR FLASH, Serial DataFlash, NAND FLASH, SD card).

The boot sequence of linux4SAM is done in several steps :

The ROM bootloader checks if a valid application is present in FLASH and if it is the case downloads it into internal SRAM. This program is usually a second level bootloader called AT91BootStrap.
AT91Bootstrap is the second level bootloader. It is in charge of the hardware configuration. It downloads U-Boot / Barebox binary from FLASH to SDRAM / DDRAM and starts the third level bootloader (U-Boot / Barebox)

(see http://www.at91.com/linux4sam/bin/view/Linux4SAM/AT91Bootstrap).

The third level bootloader is either U-Boot or Barebox. The third level bootloader is in charge of downloading NuttX binary from FLASH, network, SD card, etc. It then starts NuttX.
Then NuttX runs from SDRAM

NAND FLASH Memory Map

Reference: http://www.at91.com/linux4sam/bin/view/Linux4SAM/GettingStarted

0x0000:0000 - 0x0003:ffff: AT91BootStrap
0x0004:0000 - 0x000b:ffff: U-Boot
0x000c:0000 - 0x000f:ffff: U-Boot environment
0x0010:0000 - 0x0017:ffff: U-Boot environment redundant
0x0018:0000 - 0x001f:ffff: Device tree (DTB)
0x0020:0000 - 0x007f:ffff: NuttX
0x0080:0000 - end:         Available for use as a NAND file system

Load NuttX with U-Boot on AT91 boards

Reference http://www.at91.com/linux4sam/bin/view/Linux4SAM/U-Boot

Preparing NuttX image

U-Boot does not support normal binary images. Instead you have to create an nuttx.bin file. The NuttX build generates this file automatically. Copy it to the root of the SD Card that you made, and boot the card. The SD Card image above will automatically boot using the nuttx.bin file. If you are using another image (the Jupiter Nano linux image for instance), you can hit space to enter U-Boot, and then from the U-Boot prompt do the following:

U-Boot> fatload mmc 0 0x20008000 nuttx.bin
mci: setting clock 257812 Hz, block size 512
mci: setting clock 257812 Hz, block size 512
mci: setting clock 257812 Hz, block size 512
gen_atmel_mci: CMDR 00001048 ( 8) ARGR 000001aa (SR: 0c100025) Command Time Out
mci: setting clock 257812 Hz, block size 512
mci: setting clock 22000000 Hz, block size 512
reading nuttx.bin
108076 bytes read in 23 ms (4.5 MiB/s)

U-Boot> go 0x20008E20
## Starting application at 0x20008E20...

NuttShell (NSH) NuttX-11.0
nsh>

Buttons and LEDs

Buttons

Two buttons, labeled S1 RESET, and S2 WAKEUP are available on the Jupiter Nano. Both are connected to the Power Management Integrated Circuit (PMIC) and are not available to user programs. Pressing RESET will reset the SAMA5D27C-LD1G and the ACT8945A PMIC chips. WAKEUP is used to wake up the board if it has been put into a sleep state.

You can add your own buttons, support for pollable buttons is enabled with:

CONFIG_ARCH_BUTTONS=y

For interrupt driven buttons, add:

CONFIG_ARCH_IRQBUTTONS=y

Program interfaces for button access are described in nuttx/include/nuttx/arch.h

There is an example that can be enabled to test button interrupts. That example is enabled like:

CONFIG_EXAMPLES_BUTTONS=y
CONFIG_EXAMPLES_BUTTONS_MAX=0
CONFIG_EXAMPLES_BUTTONS_MIN=0
CONFIG_EXAMPLES_BUTTONS_NAME0="PB_USER"
CONFIG_EXAMPLES_IRQBUTTONS_MAX=0
CONFIG_EXAMPLES_IRQBUTTONS_MIN=0

LEDs

There is a blue status LED on the Jupiter Nano, driven by pin (PA6) labeled STATUS. Bringing the pin high will illuminate the LED.

------------------------------ ------------------- -------------------------
SAMA5D2 PIO                    SIGNAL              USAGE
------------------------------ ------------------- -------------------------
PA6                            STATUS_LED          Blue LED
------------------------------ ------------------- -------------------------

When CONFIG_ARCH_LEDS is defined in the NuttX configuration, NuttX will control the blue status LED as follows:

SYMBOL              Meaning                 Blue LED
------------------- ----------------------- ---------
LED_STARTED         NuttX has been started  OFF
LED_HEAPALLOCATE    Heap has been allocated OFF
LED_IRQSENABLED     Interrupts enabled      OFF
LED_STACKCREATED    Idle stack created      ON
LED_INIRQ           In an interrupt         N/C
LED_SIGNAL          In a signal handler     N/C
LED_ASSERTION       An assertion failed     N/C
LED_PANIC           The system has crashed  FLASH

Thus if the blue LED is statically on, NuttX has successfully booted and is, apparently, running normally. If LED is flashing at approximately 2Hz, then a fatal error has been detected and the system has halted.

Serial Console

The default serial console is UART1. UART1 is connected to the MCP2200 USB-UART converter, and is available as a USB serial connection on the micro-USB connector labeled CONSOLE. This is the default serial console.

------------------------ -------------
SCHEMATIC                   SAMA5D2
NAME(s)                  PIO  FUNCTION
------------------------ -------------
UART1_RX  DBGU_UTXD1_PD3 PD3  UTXD1
UART1_TX  DBGU_URXD1_PD2 PD2  URXD1
------------------------ -------------

The other UARTS on the connectors (J5 and J6) are FLEXCOMS 0, 2, 3 and 4. Terminology: FLEXCOM is the same as USART in previous SAMA5D versions. These can be configured as UARTs, SPI interfaces, or TWI interfaces.

----  -----------       -------------
       BOARD            SAMA5D2
PIN    NAME             PIO  FUNCTION
----  ----------------- -------------
J6 15 FLEXCOM0_IO0_PB28 PB28 FLEXCOM0
J6 16 FLEXCOM0_IO0_PB29 PB29 FLEXCOM0
J5 39 FLEXCOM2_IO0_PD26 PD26 FLEXCOM2
J5 40 FLEXCOM2_IO0_PD27 PA27 FLEXCOM2
J5 45 FLEXCOM3_IO0_PA15 PA15 FLEXCOM3
J5 46 FLEXCOM3_IO0_PA13 PA13 FLEXCOM3
J6 20 FLEXCOM4_IO0_PD12 PD12 FLEXCOM4
J6 21 FLEXCOM4_IO0_PD13 PD13 FLEXCOM4
----  ---------------- -------------

By default, the standard UART on the connectors (FLEXCOM4) is enabled in all of these configurations unless otherwise noted.

Jupiter Nano 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_CORTEXA5=y

CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory

CONFIG_ARCH_CHIP="sama5"

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

CONFIG_ARCH_CHIP_SAMA5=y
CONFIG_ARCH_CHIP_ATSAMA5D27=y

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

CONFIG_ARCH_BOARD="jupiter-nano" (for the Starcat Jupiter Nano)

CONFIG_ARCH_BOARD_name - For use in C code

CONFIG_ARCH_BOARD_GIANT_BOARD=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 DRAM (SRAM in this case):

CONFIG_RAM_SIZE=0x0002000 (128Kb)

CONFIG_RAM_START - The physical start address of installed DRAM

CONFIG_RAM_START=0x20000000

CONFIG_RAM_VSTART - The virtual start address of installed DRAM

CONFIG_RAM_VSTART=0x20000000

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:

REVISIT: Unverified, cloned text from the SAMA5D4-EK README.txt

CONFIG_SAMA5_DBGU        - Debug Unit
CONFIG_SAMA5_PIT         - Periodic Interval Timer
CONFIG_SAMA5_WDT         - Watchdog timer
CONFIG_SAMA5_HSMC        - Multi-bit ECC
CONFIG_SAMA5_SMD         - SMD Soft Modem
CONFIG_SAMA5_FLEXCOM0    - Flexcom 0
CONFIG_SAMA5_FLEXCOM1    - Flexcom 0
CONFIG_SAMA5_FLEXCOM2    - Flexcom 0
CONFIG_SAMA5_FLEXCOM3    - Flexcom 0
CONFIG_SAMA5_FLEXCOM4    - Flexcom 0
CONFIG_SAMA5_UART0       - UART 0 (not available on the pins)
CONFIG_SAMA5_UART1       - UART 1
CONFIG_SAMA5_UART2       - UART 2 (not available on the pins)
CONFIG_SAMA5_UART3       - UART 3 (not available on the pins)
CONFIG_SAMA5_UART4       - UART 4 (not available on the pins)
CONFIG_SAMA5_TWI0        - Two-Wire Interface 0
CONFIG_SAMA5_TWI1        - Two-Wire Interface 1
CONFIG_SAMA5_SDMMC0      - SD MMC card interface 0 (not available on the pins)
CONFIG_SAMA5_SDMMC1      - SD MMC card interface 1
CONFIG_SAMA5_SPI0        - Serial Peripheral Interface 0
CONFIG_SAMA5_SPI1        - Serial Peripheral Interface 1
CONFIG_SAMA5_TC0         - Timer Counter 0 (ch. 0, 1, 2)
CONFIG_SAMA5_TC1         - Timer Counter 1 (ch. 3, 4, 5)
CONFIG_SAMA5_PWM         - Pulse Width Modulation Controller
CONFIG_SAMA5_ADC         - Touch Screen ADC Controller
CONFIG_SAMA5_XDMAC0      - XDMA Controller 0
CONFIG_SAMA5_XDMAC1      - XDMA Controller 1
CONFIG_SAMA5_UHPHS       - USB Host High Speed
CONFIG_SAMA5_UDPHS       - USB Device High Speed
CONFIG_SAMA5_EMAC0       - Ethernet MAC 0 (GMAC0) (not available on the pins)
CONFIG_SAMA5_EMAC1       - Ethernet MAC 1 (GMAC1) (not available on the pins)
CONFIG_SAMA5_LCDC        - LCD Controller (not available on the pins)
CONFIG_SAMA5_ISI         - Image Sensor Interface (not available on the pins)
CONFIG_SAMA5_SSC0        - Synchronous Serial Controller 0
CONFIG_SAMA5_SSC1        - Synchronous Serial Controller 1
CONFIG_SAMA5_SHA         - Secure Hash Algorithm
CONFIG_SAMA5_AES         - Advanced Encryption Standard
CONFIG_SAMA5_TDES        - Triple Data Encryption Standard
CONFIG_SAMA5_TRNG        - True Random Number Generator
CONFIG_SAMA5_ARM         - Performance Monitor Unit
CONFIG_SAMA5_FUSE        - Fuse Controller
CONFIG_SAMA5_MPDDRC      - MPDDR controller

Some subsystems can be configured to operate in different ways. The drivers need to know how to configure the subsystem.

CONFIG_SAMA5_PIOA_IRQ    - Support PIOA interrupts
CONFIG_SAMA5_PIOB_IRQ    - Support PIOB interrupts
CONFIG_SAMA5_PIOC_IRQ    - Support PIOD interrupts
CONFIG_SAMA5_PIOD_IRQ    - Support PIOD interrupts

CONFIG_USART0_SERIALDRIVER - Flexcom0 is configured as a UART
CONFIG_USART1_SERIALDRIVER - Flexcom1 is configured as a UART
CONFIG_USART2_SERIALDRIVER - Flexcom2 is configured as a UART
CONFIG_USART3_SERIALDRIVER - Flexcom3 is configured as a UART
CONFIG_USART4_SERIALDRIVER - Flexcom4 is configured as a UART

AT91SAMA5 specific device driver settings

CONFIG_SAMA5_DBGU_SERIAL_CONSOLE - selects the DBGU
  for the console and ttyDBGU
CONFIG_SAMA5_DBGU_RXBUFSIZE - Characters are buffered as received.
   This specific the size of the receive buffer
CONFIG_SAMA5_DBGU_TXBUFSIZE - Characters are buffered before
   being sent. This specific the size of the transmit buffer
CONFIG_SAMA5_DBGU_BAUD - The configure BAUD of the DBGU.
CONFIG_SAMA5_DBGU_PARITY - 0=no parity, 1=odd parity, 2=even parity

CONFIG_U[S]ARTn_SERIAL_CONSOLE - selects the USARTn (n=0,1,2,3) or UART
       m (m=4,5) for the console and ttys0 (default is the DBGU).
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_PARITY - 0=no parity, 1=odd parity, 2=even parity
CONFIG_U[S]ARTn_2STOP - Two stop bits

AT91SAMA5 USB Host Configuration

Pre-requisites

CONFIG_USBDEV          - Enable USB device support
CONFIG_USBHOST         - Enable USB host support
CONFIG_SAMA5_UHPHS     - Needed
CONFIG_SAMA5_OHCI      - Enable the STM32 USB OTG FS block
CONFIG_SCHED_WORKQUEUE - Worker thread support is required

Options:

CONFIG_SAMA5_OHCI_NEDS
  Number of endpoint descriptors
CONFIG_SAMA5_OHCI_NTDS
  Number of transfer descriptors
CONFIG_SAMA5_OHCI_TDBUFFERS
  Number of transfer descriptor buffers
CONFIG_SAMA5_OHCI_TDBUFSIZE
  Size of one transfer descriptor buffer
CONFIG_USBHOST_INT_DISABLE
  Disable interrupt endpoint support
CONFIG_USBHOST_ISOC_DISABLE
  Disable isochronous endpoint support
CONFIG_USBHOST_BULK_DISABLE
  Disable bulk endpoint support

config SAMA5_OHCI_REGDEBUG

Configurations

Information Common to All Configurations

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

tools/configure.sh jupiter-nano:<subdir>

Before building, make sure the PATH environment variable includes the correct path to the directory than holds your toolchain binaries.

And then build NuttX by simply typing the following. At the conclusion of the make, the nuttx binary will reside in an ELF file called, simply, nuttx.

make

The that is provided above as an argument to the tools/configure.sh must be is one of the following.

NOTES:

These configurations use the mconf-based configuration tool. To change any of these configurations 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.

Unless stated otherwise, all configurations generate console output on the DBGU (J23).
All of these configurations use the Code Sourcery for Windows toolchain (unless stated otherwise in the description of the configuration). That toolchain selection can easily be reconfigured using 'make menuconfig'. Here are the relevant current settings:

Build Setup:

CONFIG_HOST_WINDOWS=y               : Microsoft Windows
CONFIG_WINDOWS_CYGWIN=y             : Using Cygwin or other POSIX environment

System Type -> Toolchain:

CONFIG_ARMV7A_TOOLCHAIN_GNU_EABIW=y : GNU EABI toolchain for windows

The SAMA5Dx is running at 528MHz by default in these configurations.

Board Selection -> CPU Frequency

CONFIG_SAMA5D2XULT_528MHZ=y       : Enable 528MHz operation
CONFIG_BOARD_LOOPSPERMSEC=65775   : Calibrated on SAMA5D3-Xplained at 528MHz running from SDRAM

Configuration Sub-directories

Summary: Some of the descriptions below are long and wordy. Here is the concise summary of the available Jupiter Nano configurations:

nsh:

This is a basic NuttShell (NSH) configuration.

There may be issues with some of these configurations. See the details for status of individual configurations.

Now for the gory details:

netnsh:

This is a network enabled configuration based on the NuttShell (NSH). The CDC-ECM driver is enabled, so you can plug a USB cable into the USB-Micro port (USB-A) and the board will appear as an CDC-ECM ethernet adapter.
nsh:

This configuration directory provide the NuttShell (NSH). This is a very simple NSH configuration upon which you can build further functionality.

NOTES:
1. This configuration uses the UART1 (PD2 and PD3) for the serial console. USART1 is available at the "DBGU" RS-232 connector (J24). This is easily changed by reconfiguring to (1) enable a different serial peripheral, and (2) selecting that serial peripheral as the console device.
2. By default, this configuration is set up to build on Windows under either a Cygwin or MSYS environment using a recent, Windows- native, generic ARM EABI GCC toolchain (such as the ARM supported toolchain). Both the build environment and the toolchain selection can easily be changed by reconfiguring:
  
  CONFIG_HOST_WINDOWS=y : Windows operating system CONFIG_WINDOWS_CYGWIN=y : POSIX environment under windows CONFIG_ARMV7A_TOOLCHAIN_EABIW=y : Generic GCC EABI toolchain for Windows
  
  If you are running on Linux, make certain that you have CONFIG_HOST_LINUX=y before the first make or you will create a corrupt configuration that may not be easy to recover from. See the warning in the section "Information Common to All Configurations" for further information.
3. This configuration supports logging of debug output to a circular buffer in RAM. This feature is discussed fully in this Wiki page: http://nuttx.org/doku.php?id=wiki:howtos:syslog . Relevant configuration settings are summarized below:
  
  File System:
  
  Device Drivers: CONFIG_RAMLOG=y : Enable the RAM-based logging feature. CONFIG_RAMLOG_SYSLOG=y : This enables the RAM-based logger as the system logger. CONFIG_RAMLOG_NONBLOCKING=y : Needs to be non-blocking for dmesg CONFIG_RAMLOG_BUFSIZE=16384 : Buffer size is 16KiB
  
  NOTE: This RAMLOG feature is really only of value if debug output is enabled. But, by default, no debug output is disabled in this configuration. Therefore, there is no logic that will add anything to the RAM buffer. This feature is configured and in place only to support any future debugging needs that you may have.
  
  If you don't plan on using the debug features, then by all means disable this feature and save 16KiB of RAM!
  
  NOTE: There is an issue with capturing data in the RAMLOG: If the system crashes, all of the crash dump information will into the RAMLOG and you will be unable to access it! You can tell that the system has crashed because (a) it will be unresponsive and (b) the RED LED will be blinking at about 2Hz.
  
  That is another good reason to disable the RAMLOG!
4. This configuration executes out of SDRAM flash and is loaded into SDRAM from SD card U-Boot. Data also is positioned in SDRAM.
  
  Booting with U-Boot from nuttx.bin on an SD card is the only boot method that has been tested. These are the commands that I used to boot NuttX from the SD card:
  
  U-Boot> fatload mmc 0 0x20008000 nuttx.bin U-Boot> go 0x20008E20
5. This configuration supports /dev/null, /dev/zero, and /dev/random.
  
  CONFIG_DEV_NULL=y : Enables /dev/null CONFIG_DEV_ZERO=y : Enabled /dev/zero
  
  Support for /dev/random is implemented using the SAMA5D2's True Random Number Generator (TRNG). See the section above entitled "TRNG and /dev/random" for information about configuring /dev/random.
  
  CONFIG_SAMA5_TRNG=y : Enables the TRNG peripheral CONFIG_DEV_RANDOM=y : Enables /dev/random
6. This configuration has support for NSH built-in applications enabled. No built-in applications are enabled, however.
7. This configuration has support for the FAT and PROCFS file systems built in.
  
  The FAT file system includes long file name support. Please be aware that Microsoft claims patents against the long file name support (see more discussion in the top-level NOTICE file).
  
  CONFIG_FS_FAT=y : Enables the FAT file system CONFIG_FAT_LCNAMES=y : Enable lower case 8.3 file names CONFIG_FAT_LFN=y : Enables long file name support CONFIG_FAT_MAXFNAME=32 : Arbitrarily limits the size of a path segment name to 32 bytes
  
  The PROCFS file system is enabled simply with:
  
  CONFIG_FS_PROCFS=y : Enable PROCFS file system
8. The Real Time Clock/Calendar (RTC) is enabled in this configuration. See the section entitled "RTC" above for detailed configuration settings.
  
  The RTC alarm is not enabled by default since there is nothing in this configuration that uses it. The alarm can easily be enabled, however, as described in the "RTC" section.
  
  The time value from the RTC will be used as the NuttX system time in all timestamp operations. You may use the NSH 'date' command to set or view the RTC as described above in the "RTC" section.
  
  NOTE: If you want the RTC to preserve time over power cycles, you will need to install a battery in the battery holder (J12) and close the jumper, JP13.
sdmmc-net-nsh:

This is a configuration based on the NuttShell (NSH). Internet networking and the SDMMC peripheral is enabled. NuttX can read and write to a VFAT filesystem on the SD Card.

NuttX will mount the SD Card at /mnt/mmcsd1.

Networking

Jupiter Nano has support for Ethernet over USB using CDC-ECM protocol. (All the SAMA5D27C boards do, actually.) The Jupiter Nano will appear as an Ethernet USB Gadget on the Linux side. This is a high performance link and can transfer 30MB/s of data to or from a host computer.

The netnsh sdmmcnsh, or sdmmc-nsh-net-resolvconf configurations will set up the Ethernet over USB interface to be 10.0.0.2, and set up default routing via 10.0.0.1. The sdmmc-nsh-net-resolvconf also sets up the /etc/resolv.conf file and configures NuttX to support it, which enables DNS resolution using Google's open DNS servers.

The tools/netusb.sh script can set up a Linux computer with IP tables NAT rules and proper routes to allow the NuttX computer to access the Internet, setting the Linux side of the Ethernet over USB link to have the IP address of 10.0.0.1.

In the commands below, replace the interface identifier wlp0s20f3 with the interface that you use to access the Internet.

$./tools/netusb.sh show
enx020000112233: flags=4098<BROADCAST,MULTICAST>  mtu 1500
        inet 10.0.0.1  netmask 255.255.255.0  broadcast 10.0.0.255
        ether 02:00:00:11:22:33  txqueuelen 1000  (Ethernet)
        RX packets 4  bytes 256 (256.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 119  bytes 15694 (15.6 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

$ sudo ./tools/netusb.sh wlp0s20f3 enx020000112233 on
default via 192.168.1.1 dev wlp0s20f3 proto dhcp metric 600
169.254.0.0/16 dev br-cc496150b4da scope link metric 1000 linkdown
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown
172.18.0.0/16 dev br-cc496150b4da proto kernel scope link src 172.18.0.1 linkdown
192.168.1.0/24 dev wlp0s20f3 proto kernel scope link src 192.168.1.209 metric 600

enx020000112233: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        ether 02:00:00:11:22:33  txqueuelen 1000  (Ethernet)
        RX packets 4  bytes 256 (256.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 119  bytes 15694 (15.6 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0


default via 192.168.1.1 dev wlp0s20f3 proto dhcp metric 600
10.0.0.0/24 dev enx020000112233 scope link src 10.0.0.1
10.0.0.0/24 dev enx020000112233 proto kernel scope link src 10.0.0.1 metric 100
10.0.0.0/8 dev enx020000112233 proto kernel scope link src 10.0.0.1
10.0.0.2 dev enx020000112233 scope link src 10.0.0.1
169.254.0.0/16 dev br-cc496150b4da scope link metric 1000 linkdown
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown
172.18.0.0/16 dev br-cc496150b4da proto kernel scope link src 172.18.0.1 linkdown
192.168.1.0/24 dev wlp0s20f3 proto kernel scope link src 192.168.1.209 metric 600

PING 10.0.0.2 (10.0.0.2) 56(84) bytes of data.
64 bytes from 10.0.0.2: icmp_seq=1 ttl=64 time=0.187 ms

--- 10.0.0.2 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.187/0.187/0.187/0.000 ms