NuttX RTOS Porting Guide

Last Updated: December 12, 2009

Table of Contents

1.0 Introduction

Overview This document provides and overview of the NuttX build and configuration logic and provides hints for the incorporation of new processor/board architectures into the build.

See also arch/README.txt and configs/README.txt.

2.0 Directory Structure

Directory Structure. The general directly layout for NuttX is very similar to the directory structure of the Linux kernel -- at least at the most superficial layers. At the top level is the main makefile and a series of sub-directories identified below and discussed in the following paragraphs:

Configuration Files. The NuttX configuration consists of:

2.1 Documentation

General documentation for the NuttX OS resides in this directory.

2.2 arch

2.2.1 Subdirectory Structure

This directory contains several sub-directories, each containing architecture-specific logic. The task of porting NuttX to a new processor consists of add a new subdirectory under arch/ containing logic specific to the new architecture. The complete board port in is defined by the architecture-specific code in this directory (plus the board-specific configurations in the config/ subdirectory). Each architecture must provide a subdirectory, <arch-name> under arch/ with the following characteristics:

2.2.2 Summary of Files

2.2.3 Supported Architectures

Architecture- and Chip-Specific Directories. All processor architecture-specific directories are maintained in sub-directories of the arch/ directory. Different chips or SoC's may implement the same processor core. Chip-specific logic can be found in sub-directories under the architecture directory. Current architecture/chip directories are summarized below:

Deprecated Architecture Directories. The following architecture directories are deprecated. They have been replaced by the logic in arm/arm and will deleted when arch/arm is fully verified.

Other ports for the for the TI TMS320DM270 and for MIPS are in various states of progress

2.3 binfmt

The binfmt/ subdirectory contains logic for loading binaries in the file system into memory in a form that can be used to execute them.

2.4 configs

The configs/ subdirectory contains configuration data for each board. These board-specific configurations plus the architecture-specific configurations in the arch/ subdirectory complete define a customized port of NuttX.

2.3.1 Subdirectory Structure

The configs directory contains board specific configuration files. Each board must provide a subdirectory <board-name> under configs/ with the following characteristics: 

    <board-name>
|-- include/
|   |-- board.h
|   `-- (board-specific header files)
|-- src/
|   |-- Makefile
|   `-- (board-specific source files)
|-- <config1-dir>
|   |-- Make.defs
|   |-- defconfig
|   `-- setenv.sh
|-- <config2-dir>
|   |-- Make.defs
|   |-- defconfig
|   `-- setenv.sh
|   ...
`-- (other board-specific configuration sub-directories)/

2.3.2 Summary of Files

2.3.2.1 Board Specific Logic

  • include/: This directory contains board specific header files. This directory will be linked as include/arch/board at configuration time and can be included via #include <arch/board/header.h>. These header file can only be included by files in arch/<arch-name>/include/ and arch/<arch-name>/src/.
  • src/: This directory contains board specific drivers. This directory will be linked as arch/<arch-name>/src/board at configuration time and will be integrated into the build system.
  • src/Makefile: This makefile will be invoked to build the board specific drivers. It must support the following targets: libext$(LIBEXT), clean, and distclean.

2.3.2.2 Board Specific Configuration Sub-Directories

The configs/<board-name>/ sub-directory holds all of the files that are necessary to configure NuttX for the particular board. A board may have various different configurations using the common source files. Each board configuration is described by three files: Make.defs, defconfig, and setenv.sh. Typically, each set of configuration files is retained in a separate configuration sub-directory (<config1-dir>, <config2-dir>, .. in the above diagram). The procedure for configuring NuttX is described below, This paragraph will describe the contents of these configuration files.

  • Make.defs: This makefile fragment provides architecture and tool-specific build options. It will be included by all other makefiles in the build (once it is installed). This make fragment should define:
    • Tools: CC, LD, AR, NM, OBJCOPY, OBJDUMP
    • Tool options: CFLAGS, LDFLAGS
    • COMPILE, ASSEMBLE, ARCHIVE, CLEAN, and MKDEP macros

    When this makefile fragment runs, it will be passed TOPDIR which is the path to the root directory of the build. This makefile fragment may include ${TOPDIR}/.config to perform configuration specific settings. For example, the CFLAGS will most likely be different if CONFIG_DEBUG=y.

  • defconfig: This is a configuration file similar to the Linux configuration file. In contains variable/value pairs like:
    • CONFIG_VARIABLE=value

    This configuration file will be used at build time:

    1. As a makefile fragment included in other makefiles, and
    2. to generate include/nuttx/config.h which is included by most C files in the system.
  • setenv.sh: This is a script that you can include that will be installed at the top level of the directory structure and can be sourced to set any necessary environment variables.

2.3.3 Supported Boards

All of the specific boards supported by NuttX are identified below. These are the specific <board-name>'s that may be used to configure NuttX as described below.

  • configs/c5471evm: This is a port to the Spectrum Digital C5471 evaluation board. The C5471 is a dual core processor from TI with an ARM7TDMI general purpose processor and a c54 SDP. NuttX runs on the ARM core and is built with with a GNU arm-elf toolchain* under Linux or Cygwin. This port is complete, verified, and included in the NuttX release.
  • configs/ez80f0910200kitg ez80Acclaim! Microcontroller. This port use the Zilog ez80f0910200kitg development kit, eZ80F091 part, and the Zilog ZDS-II Windows command line tools. The development environment is Cygwin under WinXP.
  • configs/m68322evb: This is a work in progress for the venerable m68322evb board from Motorola.
  • configs/mcu123-lpc214x: This port is for the NXP LPC2148 as provided on the mcu123.com lpc214x development board. This OS is also built with the arm-elf toolchain* under Linux or Cygwin. The port supports serial, timer0, spi, and usb.
  • configs/ntosd-dm320: This port uses the Neuros OSD with a GNU arm-elf toolchain* under Linux or Cygwin. See Neuros Wiki for further information. NuttX operates on the ARM9EJS of this dual core processor. STATUS: This port is code complete, verified, and included in the NuttX 0.2.1 release.
  • configs/olimex-strp711: This port uses the Olimex STR-P711 board arm-elf toolchain* under Linux or Cygwin. See the Olimex web site for further information. STATUS: Coding for the basic port -- serial console and system timer -- is complete but untested to problems I am having using OpenOCD with a wiggler clone JTAG.
  • configs/pjrc-8051: 8051 Microcontroller. This port uses the PJRC 87C52 development system and the SDCC toolchain under Linux or Cygwin. This port is not quite ready for prime time.
  • configs/sim: A user-mode port of NuttX to the x86 Linux platform is available. The purpose of this port is primarily to support OS feature development. This port does not support interrupts or a real timer (and hence no round robin scheduler) Otherwise, it is complete.
  • configs/us7032evb1: This is a port of the Hitachi SH-1 on the Hitachi SH-1/US7032EVB1 board. STATUS: This port is available as of release 0.3.18 of NuttX. The port is basically complete and many examples run correctly. However, there are remaining instabilities that make the port un-usable. The nature of these is not understood; the behavior is that certain SH-1 instructions stop working as advertised. This could be a silicon problem, some pipeline issue that is not handled properly by the gcc 3.4.5 toolchain (which has very limited SH-1 support to begin with), or perhaps with the CMON debugger. At any rate, I have exhausted all of the energy that I am willing to put into this cool old processor for the time being.
  • configs/xtrs: TRS80 Model 3. This port uses a vintage computer based on the Z80. An emulator for this computer is available to run TRS80 programs on a Linux platform (http://www.tim-mann.org/xtrs.html).
  • configs/z16f2800100zcog z16f Microcontroller. This port use the Zilog z16f2800100zcog development kit and the Zilog ZDS-II Windows command line tools. The development environment is Cygwin under WinXP.
  • configs/z80sim: z80 Microcontroller. This port uses a Z80 instruction set simulator. That simulator can be found in the NuttX CVS here. This port also the SDCC toolchain under Linux or Cygwin(verified with version 2.6.0).
  • configs/z8encore000zco z8Encore! Microcontroller. This port use the Zilog z8encore000zco development kit, Z8F6403 part, and the Zilog ZDS-II Windows command line tools. The development environment is Cygwin under WinXP.
  • configs/z8encore000zco z8Encore! Microcontroller. This port use the Zilog z8f64200100kit development kit, Z8F6423 part, and the Zilog ZDS-II Windows command line tools. The development environment is Cygwin under WinXP.

* A customized version of the buildroot is available to build these toolchains under Linux or Cygwin.

2.5 drivers

This directory holds architecture-independent device drivers. 

    drivers/
|-- Makefile
|-- bch/
|   |-- Make.defs
|   `-- (bch driver source files)
|-- mmcsd/
|   |-- Make.defs
|   `-- (mmcsd driver source files)
|-- net/
|   |-- Make.defs
|   `-- (net driver source files)
|-- usbdev/
|   |-- Make.defs
|   `-- (usbdev driver source files)
`-- (common driver source files)

2.6 examples

Example and test programs to build against.

2.7 fs

This directory contains the NuttX file system. This file system is described below. 

    fs/
|-- Makefile
|-- fat/
|   |-- Make.defs
|   `-- (fat file system source files)
|-- romfs/
|   |-- Make.defs
|   `-- (romfs file system source files)
 `-- (common file system source files)

2.8 graphics

This directory contains files for graphics/video support under NuttX. 

    graphics/
|-- Makefile
|-- nxglib/
|   |-- Make.defs
|   `-- (NuttX graphics library source files)
|-- nx/
|   |-- Make.defs
|   `-- (NuttX X-server source files)
`-- (common file system source files)

2.9 include

This directory holds NuttX header files. Standard header files file retained in can be included in the normal fashion:

    include <stdio.h>
    include <sys/types.h>
    etc.

Directory structure: 

    include/
|-- (standard header files)
|-- arpa/
|   `-- (standard header files)
|-- net/
|   `-- uip/
|       `-- (uIP specific header files)
|-- netinet/
|   `-- (standard header files)
|-- nuttx/
|   `-- (nuttx specific header files)
`- sys/
    `-- (more standard header files)

2.10 lib

This directory holds a collection of standard libc-like functions with custom interfaces into NuttX.

2.11 libxx

This directory holds a tiny, minimal standard std C++ that can be used to build some, simple C++ applications in NuttX.

2.12 mm

This is the NuttX memory manager.

2.13 net

This directory contains the implementation of the socket APIs. The subdirectory, uip contains the uIP port.

2.14 netutils

This directory contains most of the network applications. Some of these are original with NuttX (like tftpc and dhcpd) and others were leveraged from the uIP-1.0 apps directory. As the uIP apps/README says, these applications "are not all heavily tested." 

    netutils/
|-- Makefile
|-- dhcp/
|   |-- Make.defs
|   `-- (dhcp source files)
|-- dhcpd/
|   |-- Make.defs
|   `-- (dhcpd source files)
|-- resolv/
|   |-- Make.defs
|   `-- (resolv source files)
|-- smtp/
|   |-- Make.defs
|   `-- (smtp source files)
|-- telnetd/
|   |-- Make.defs
|   `-- (telnetd source files)
|-- tftpc/
|   |-- Make.defs
|   `-- (tftpc source files)
|-- uiplib/
|   |-- Make.defs
|   `-- (uiplib source files)
|-- weblclient/
|   |-- Make.defs
|   `-- (webclient source files)
|-- webserver/
|   |-- Make.defs
|   `-- (webserver source files)
`-- (netutils common files)

2.15 sched

The files forming core of the NuttX RTOS reside here.

2.16 tools

This directory holds a collection of tools and scripts to simplify configuring, building and maintaining NuttX. 

    tools/
|-- Makefile.mkconfig
|-- configure.sh
|-- incdir.sh
|-- indent.sh
|-- link.sh
|-- mkconfig.c
|-- mkdeps.sh
|-- mkimage.sh
|-- mknulldeps.sh
|-- unlink.sh
|-- winlink.sh
`-- zipme

2.17 Makefile

The top-level Makefile in the ${TOPDIR} directory contains all of the top-level control logic to build NuttX. Use of this Makefile to build NuttX is described below.

3.0 Configuring and Building

3.1 Configuring NuttX

Manual Configuration. Configuring NuttX requires only copying the board-specific configuration files into the top level directory which appears in the make files as the make variable, ${TOPDIR}. This could be done manually as follows:

  • Copy configs/<board-name>/[<config-dir>/]Make.def to ${TOPDIR}/Make.defs,
  • Copy configs/<board-name>/[<config-dir>/]setenv.sh to ${TOPDIR}/setenv.sh, and
  • Copy configs/<board-name>/[<config-dir>/]defconfig to ${TOPDIR}/.config

Where <board-name> is the name of one of the sub-directories of the NuttX configs/ directory. This sub-directory name corresponds to one of the supported boards identified above. And <config-dir> is the optional, specific configuration directory for the board.

Automated Configuration. There is a script that automates these steps. The following steps will accomplish the same configuration: 

      cd tools
  ./configure.sh <board-name>[/<config-dir>]

Additional Configuration Steps. The remainder of configuration steps will be performed by ${TOPDIR}/Makefile the first time the system is built as described below.

3.2 Building NuttX

Building NuttX. Once NuttX has been configured as described above, it may be built as follows: 

    cd ${TOPDIR}
source ./setenv.sh
make

The ${TOPDIR} directory holds:

  • The top level Makefile that controls the NuttX build.

That directory also holds:

  • The makefile fragment .config that describes the current configuration.
  • The makefile fragment Make.defs that provides customized build targets, and
  • The shell script setenv.sh that sets up the configuration environment for the build.

The setenv.sh contains Linux/Cygwin environmental settings that are needed for the build. The specific environmental definitions are unique for each board but should include, as a minimum, updates to the PATH variable to include the full path to the architecture-specific toolchain identified in Make.defs. The setenv.sh only needs to be source'ed at the beginning of a session. The system can be re-made subsequently by just typing make.

First Time Make. Additional configuration actions will be taken the first time that system is built. These additional steps include:

  • Auto-generating the file include/nuttx/config. using the ${TOPDIR}/.config file.
  • Creating a link to ${TOPDIR}/arch/<arch-name>/include at ${TOPDIR}/include/arch.
  • Creating a link to ${TOPDIR}/configs/<board-name>/include at ${TOPDIR}/include/arch/board.
  • Creating a link to ${TOPDIR}/configs/<board-name>/src at ${TOPDIR}/arch/<arch-name>/src/board
  • Creating make dependencies.

4.0 Architecture APIs

The file include/nuttx/arch.h identifies by prototype all of the APIs that must be provided by the architecture specific logic. The internal OS APIs that architecture-specific logic must interface with also also identified in include/nuttx/arch.h or in other header files.

4.1 APIs Exported by Architecture-Specific Logic to NuttX

4.1.1 up_initialize()

Prototype: void up_initialize(void);

Description. up_initialize() will be called once during OS initialization after the basic OS services have been initialized. The architecture specific details of initializing the OS will be handled here. Such things as setting up interrupt service routines, starting the clock, and registering device drivers are some of the things that are different for each processor and hardware platform.

up_initialize() is called after the OS initialized but before the init process has been started and before the libraries have been initialized. OS services and driver services are available.

4.1.2 up_idle()

Prototype: void up_idle(void);

Description. up_idle() is the logic that will be executed when their is no other ready-to-run task. This is processor idle time and will continue until some interrupt occurs to cause a context switch from the idle task.

Processing in this state may be processor-specific. e.g., this is where power management operations might be performed.

4.1.3 up_initial_state()

Prototype: void up_initial_state(FAR _TCB *tcb);

Description. A new thread is being started and a new TCB has been created. This function is called to initialize the processor specific portions of the new TCB.

This function must setup the initial architecture registers and/or stack so that execution will begin at tcb->start on the next context switch.

4.1.4 up_create_stack()

Prototype: STATUS up_create_stack(FAR _TCB *tcb, size_t stack_size);

Description. Allocate a stack for a new thread and setup up stack-related information in the TCB.

The following TCB fields must be initialized:

  • adj_stack_size: Stack size after adjustment for hardware, processor, etc. This value is retained only for debug purposes.
  • stack_alloc_ptr: Pointer to allocated stack
  • adj_stack_ptr: Adjusted stack_alloc_ptr for HW. The initial value of the stack pointer.

This API is NOT required if CONFIG_CUSTOM_STACK is defined.

Inputs:

  • tcb: The TCB of new task.
  • stack_size: The requested stack size. At least this much must be allocated.

    • 4.1.5 up_use_stack()

    Prototype: STATUS up_use_stack(FAR _TCB *tcb, FAR void *stack, size_t stack_size);

    Description. Setup up stack-related information in the TCB using pre-allocated stack memory.

    The following TCB fields must be initialized:

    • adj_stack_size: Stack size after adjustment for hardware, processor, etc. This value is retained only for debug purposes.
    • stack_alloc_ptr: Pointer to allocated stack
    • adj_stack_ptr: Adjusted stack_alloc_ptr for HW. The initial value of the stack pointer.

    This API is NOT required if CONFIG_CUSTOM_STACK is defined.

    Inputs:

    • tcb: The TCB of new task.
    • stack_size: The allocated stack size.

    4.1.6 up_release_stack()

    Prototype: void up_release_stack(FAR _TCB *dtcb);

    Description. A task has been stopped. Free all stack related resources retained int the defunct TCB.

    This API is NOT required if CONFIG_CUSTOM_STACK is defined.

    4.1.7 up_unblock_task()

    Prototype: void up_unblock_task(FAR _TCB *tcb);

    Description. A task is currently in an inactive task list but has been prepped to execute. Move the TCB to the ready-to-run list, restore its context, and start execution.

    This function is called only from the NuttX scheduling logic. Interrupts will always be disabled when this function is called.

    Inputs:

    • tcb: Refers to the tcb to be unblocked. This tcb is in one of the waiting tasks lists. It must be moved to the ready-to-run list and, if it is the highest priority ready to run tasks, executed.

    4.1.8 up_block_task()

    Prototype: void up_block_task(FAR _TCB *tcb, tstate_t task_state);

    Description. The currently executing task at the head of the ready to run list must be stopped. Save its context and move it to the inactive list specified by task_state. This function is called only from the NuttX scheduling logic. Interrupts will always be disabled when this function is called.

    Inputs:

    • tcb: Refers to a task in the ready-to-run list (normally the task at the head of the list). It most be stopped, its context saved and moved into one of the waiting task lists. It it was the task at the head of the ready-to-run list, then a context to the new ready to run task must be performed.
    • task_state: Specifies which waiting task list should be hold the blocked task TCB.

    4.1.9 up_release_pending()

    Prototype: void up_release_pending(void);

    Description. When tasks become ready-to-run but cannot run because pre-emption is disabled, they are placed into a pending task list. This function releases and makes ready-to-run all of the tasks that have collected in the pending task list. This can cause a context switch if a new task is placed at the head of the ready to run list.

    This function is called only from the NuttX scheduling logic when pre-emption is re-enabled. Interrupts will always be disabled when this function is called.

    4.1.10 up_reprioritize_rtr()

    Prototype: void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority);

    Description. Called when the priority of a running or ready-to-run task changes and the reprioritization will cause a context switch. Two cases:

    1. The priority of the currently running task drops and the next task in the ready to run list has priority.
    2. An idle, ready to run task's priority has been raised above the the priority of the current, running task and it now has the priority.

    This function is called only from the NuttX scheduling logic. Interrupts will always be disabled when this function is called.

    Inputs:

    • tcb: The TCB of the task that has been reprioritized
    • priority: The new task priority

    4.1.11 _exit()

    Prototype: void _exit(int status) noreturn_function;

    Description. This function causes the currently executing task to cease to exist. This is a special case of task_delete().

    Unlike other UP APIs, this function may be called directly from user programs in various states. The implementation of this function should disable interrupts before performing scheduling operations.

    4.1.12 up_assert()

    Prototype:
    void up_assert(FAR const ubyte *filename, int linenum);
    void up_assert_code(FAR const ubyte *filename, int linenum, int error_code);

    Description. Assertions may be handled in an architecture-specific way.

    4.1.13 up_schedule_sigaction()

    Prototype: void up_schedule_sigaction(FAR _TCB *tcb, sig_deliver_t sigdeliver);

    Description. This function is called by the OS when one or more signal handling actions have been queued for execution. The architecture specific code must configure things so that the 'sigdeliver' callback is executed on the thread specified by 'tcb' as soon as possible.

    This function may be called from interrupt handling logic.

    This operation should not cause the task to be unblocked nor should it cause any immediate execution of sigdeliver. Typically, a few cases need to be considered:

    1. This function may be called from an interrupt handler During interrupt processing, all xcptcontext structures should be valid for all tasks. That structure should be modified to invoke sigdeliver() either on return from (this) interrupt or on some subsequent context switch to the recipient task.
    2. If not in an interrupt handler and the tcb is NOT the currently executing task, then again just modify the saved xcptcontext structure for the recipient task so it will invoke sigdeliver when that task is later resumed.
    3. If not in an interrupt handler and the tcb IS the currently executing task -- just call the signal handler now.

    This API is NOT required if CONFIG_DISABLE_SIGNALS is defined.

    4.1.14 up_allocate_heap()

    Prototype: void up_allocate_heap(FAR void **heap_start, size_t *heap_size);

    Description. The heap may be statically allocated by defining CONFIG_HEAP_BASE and CONFIG_HEAP_SIZE. If these are not defined, then this function will be called to dynamically set aside the heap region.

    This API is NOT required if CONFIG_HEAP_BASE is defined.

    4.1.15 up_interrupt_context()

    Prototype: boolean up_interrupt_context(void)

    Description. Return TRUE is we are currently executing in the interrupt handler context.

    4.1.16 up_disable_irq()

    Prototype:

      #ifndef CONFIG_ARCH_NOINTC
  void up_disable_irq(int irq);
#endif

    Description. Disable the IRQ specified by 'irq' On many architectures, there are three levels of interrupt enabling: (1) at the global level, (2) at the level of the interrupt controller, and (3) at the device level. In order to receive interrupts, they must be enabled at all three levels.

    This function implements enabling of the device specified by 'irq' at the interrupt controller level if supported by the architecture (irqsave() supports the global level, the device level is hardware specific).

    If the architecture does not support up_disable_irq, CONFIG_ARCH_NOINTC should be defined in the NuttX configuration file. Since this API cannot be supported on all architectures, it should be avoided in common implementations where possible.

    4.1.17 up_enable_irq()

    Prototype:

      #ifndef CONFIG_ARCH_NOINTC
  void up_enable_irq(int irq);
#endif

    Description. This function implements disabling of the device specified by 'irq' at the interrupt controller level if supported by the architecture (irqrestore() supports the global level, the device level is hardware specific).

    If the architecture does not support up_disable_irq, CONFIG_ARCH_NOINTC should be defined in the NuttX configuration file. Since this API cannot be supported on all architectures, it should be avoided in common implementations where possible.

    4.1.18 up_prioritize_irq()

    Prototype:

      #ifdef CONFIG_ARCH_IRQPRIO
  void up_enable_irq(int irq);
#endif

    Description. Set the priority of an IRQ.

    If the architecture supports up_enable_irq, CONFIG_ARCH_IRQPRIO should be defined in the NuttX configuration file. Since this API cannot be supported on all architectures, it should be avoided in common implementations where possible.

    4.1.19 up_putc()

    Prototype: int up_putc(int ch);

    Description. This is a debug interface exported by the architecture-specific logic. Output one character on the console

    4.2 APIs Exported by NuttX to Architecture-Specific Logic

    These are standard interfaces that are exported by the OS for use by the architecture specific logic.

    4.2.1 os_start()

    To be provided

    4.2.2 OS List Management APIs

    To be provided

    4.2.3 sched_process_timer()

    Prototype: void sched_process_timer(void);

    Description. This function handles system timer events. The timer interrupt logic itself is implemented in the architecture specific code, but must call the following OS function periodically -- the calling interval must be MSEC_PER_TICK.

    4.2.4 irq_dispatch()

    Prototype: void irq_dispatch(int irq, FAR void *context);

    Description. This function must be called from the architecture- specific logic in order to display an interrupt to the appropriate, registered handling logic.

    4.3 LED Support

    A board architecture may or may not have LEDs. If the board does have LEDs, then most architectures provide similar LED support that is enabled when CONFIG_ARCH_LEDS is selected in the NuttX configuration file. This LED support is part of architecture-specific logic and is not managed by the core NuttX logic. However, the support provided by each architecture is sufficiently similar that it can be documented here.

    4.3.1 Header Files

    LED-related definitions are provided in two header files:

    • LED definitions are provided for each board in the board.h that resides in the <board-name>/include/board.h file (which is also linked to include/arch/board/board.h when the RTOS is configured). Those definitions are discussed below.
    • The board-specific logic provides unique instances of the LED interfaces. This is because the implementation of LED support may be very different on different boards. Prototypes for these board-specific implementations are, however, provided in architecture-common header files. That header file is usually at <arch-name>/src/common/up_internal.h, but could be at other locations in particular architectures. These prototypes are discussed below.

    4.3.2 LED Definitions

    The implementation of LED support is very specific to a board architecture. Some boards have several LEDS, others have only one or two. Some have none. Others LED matrices and show alphanumeric data, etc. The NuttX logic does not refer to specific LEDS, rather, it refers to an event to be shown on the LEDS in whatever manner is appropriate for the board; the way that this event is presented depends upon the hardware available on the board.

    The model used by NuttX is that the board can show 8 events defined as follows in <board-name>/include/board.h: 

      #define LED_STARTED       ??
#define LED_HEAPALLOCATE  ??
#define LED_IRQSENABLED   ??
#define LED_STACKCREATED  ??
#define LED_INIRQ         ??
#define LED_SIGNAL        ??
#define LED_ASSERTION     ??
#define LED_PANIC         ??

    The specific value assigned to each pre-processor variable can be whatever makes the implementation easiest for the board logic. The meaning associated with each definition is as follows:

    • LED_STARTED is the value that describes the setting of the LEDs when the LED logic is first initialized. This LED value is set but never cleared.
    • LED_HEAPALLOCATE indicates that the NuttX heap has been configured. This is an important place in the boot sequence because if the memory is configured wrong, it will probably crash leaving this LED setting. This LED value is set but never cleared.
    • LED_IRQSENABLED indicates that interrupts have been enabled. Again, during bring-up (or if there are hardware problems), it is very likely that the system may crash just when interrupts are enabled, leaving this setting on the LEDs. This LED value is set but never cleared.
    • LED_STACKCREATED is set each time a new stack is created. If set, it means that the system attempted to start at least one new thread. This LED value is set but never cleared.
    • LED_INIRQ is set and cleared on entry and exit from each interrupt. If interrupts are working okay, this LED will have a dull glow.
    • LED_SIGNAL is set and cleared on entry and exit from a signal handler. Signal handlers are tricky so this is especially useful during bring-up or a new architecture.
    • LED_ASSERTION is set if an assertion occurs.
    • LED_PANIC will blink at around 1Hz if the system panics and hangs.

    4.3.3 Common LED interfaces

    The <arch-name>/src/common/up_internal.h probably has definitions like: 

      /* Defined in board/up_leds.c */

#ifdef CONFIG_ARCH_LEDS
extern void up_ledinit(void);
extern void up_ledon(int led);
extern void up_ledoff(int led);
#else
# define up_ledinit()
# define up_ledon(led)
# define up_ledoff(led)
#endif

    Where:

    • void up_ledinit(void) is called early in power-up initialization to initialize the LED hardware.
    • up_ledon(int led) is called to instantiate the LED presentation of the event. The led argument is one of the definitions provided in <board-name>/include/board.h.
    • up_ledoff(int ledis called to terminate the LED presentation of the event. The led argument is one of the definitions provided in <board-name>/include/board.h. Note that only LED_INIRQ, LED_SIGNAL, LED_ASSERTION, and LED_PANIC indications are terminated.

    5.0 NuttX File System

    Overview. NuttX includes an optional, scalable file system. This file-system may be omitted altogether; NuttX does not depend on the presence of any file system.

    Pseudo Root File System. Or, a simple in-memory, pseudo file system can be enabled. This simple file system can be enabled setting the CONFIG_NFILE_DESCRIPTORS option to a non-zero value (see Appendix A). This is an in-memory file system because it does not require any storage medium or block driver support. Rather, file system contents are generated on-the-fly as referenced via standard file system operations (open, close, read, write, etc.). In this sense, the file system is pseudo file system (in the same sense that the Linux /proc file system is also referred to as a pseudo file system).

    Any user supplied data or logic can be accessed via the pseudo-file system. Built in support is provided for character and block drivers in the /dev pseudo file system directory.

    Mounted File Systems The simple in-memory file system can be extended my mounting block devices that provide access to true file systems backed up via some mass storage device. NuttX supports the standard mount() command that allows a block driver to be bound to a mountpoint within the pseudo file system and to a file system. At present, NuttX supports only the VFAT file system.

    Comparison to Linux From a programming perspective, the NuttX file system appears very similar to a Linux file system. However, there is a fundamental difference: The NuttX root file system is a pseudo file system and true file systems may be mounted in the pseudo file system. In the typical Linux installation by comparison, the Linux root file system is a true file system and pseudo file systems may be mounted in the true, root file system. The approach selected by NuttX is intended to support greater scalability from the very tiny platform to the moderate platform.

    6.0 NuttX Device Drivers

    NuttX supports a variety of device drivers including:

    • Character Device Drivers,
    • Block Device Drivers, and
    • Other Specialized Drivers.
    These different device driver types are discussed in the following paragraphs. Note: device driver support requires that the in-memory, pseudo file system is enabled by setting the CONFIG_NFILE_DESCRIPTORS in the NuttX configuration file to a non-zero value.

    6.1 Character Device Drivers

    Character device drivers have these properties:

    • include/nuttx/fs.h. All structures and APIs needed to work with character drivers are provided in this header file.
    • struct file_operations. Each character device driver must implement an instance of struct file_operations. That structure defines a call table with the following methods:

        int open(FAR struct file *filp);
        int close(FAR struct file *filp);
        ssize_t read(FAR struct file *filp, FAR char *buffer, size_t buflen);
        ssize_t write(FAR struct file *filp, FAR const char *buffer, size_t buflen);
        off_t seek(FAR struct file *filp, off_t offset, int whence);
        int ioctl(FAR struct file *filp, int cmd, unsigned long arg);
        int poll(FAR struct file *filp, struct pollfd *fds, boolean setup);

    • int register_driver(const char *path, const struct file_operations *fops, mode_t mode, void *priv);. Each character driver registers itself by calling register_driver(), passing it the path where it will appear in the pseudo-file-system and it's initialized instance of struct file_operations.
    • User Access. After it has been registered, the character driver can be accessed by user code using the standard driver operations including open(), close(), read(), write(), etc.
    • Examples: drivers/dev_null.c, drivers/fifo.c, drivers/serial.c, etc.

    6.2 Block Device Drivers

    Block device drivers have these properties:

    • include/nuttx/fs.h. All structures and APIs needed to work with block drivers are provided in this header file.
    • struct block_operations. Each block device driver must implement an instance of struct block_operations. That structure defines a call table with the following methods:

        int open(FAR struct inode *inode);
        int close(FAR struct inode *inode);
        ssize_t read(FAR struct inode *inode, FAR unsigned char *buffer, size_t start_sector, unsigned int nsectors);
        ssize_t write(FAR struct inode *inode, FAR const unsigned char *buffer, size_t start_sector, unsigned int nsectors);
        int geometry(FAR struct inode *inode, FAR struct geometry *geometry);
        int ioctl(FAR struct inode *inode, int cmd, unsigned long arg);

    • int register_blockdriver(const char *path, const struct block_operations *bops, mode_t mode, void *priv);. Each block driver registers itself by calling register_blockdriver(), passing it the path where it will appear in the pseudo-file-system and it's initialized instance of struct block_operations.
    • User Access. Users do not normally access block drivers directly, rather, they access block drivers indirectly through the mount() API. The mount() API binds a block driver instance with a file system and with a mountpoint. Then the user may use the block driver to access the file system on the underlying media. Example: See the cmd_mount() implementation in examples/nsh/nsh_fscmds.c.
    • Accessing a Character Driver as a Block Device. See the loop device at drivers/loop.c. Example: See the cmd_losetup() implementation in examples/nsh/nsh_fscmds.c.
    • Accessing a Block Driver as Character Device. See the Block-to-Character (BCH) conversion logic in drivers/bch/. Example: See the cmd_dd() implementation in examples/nsh/nsh_ddcmd.c.
    • Examples. drivers/loop.c, drivers/mmcsd/mmcsd_spi.c, drivers/ramdisk.c, etc.

    6.3 Specialized Device Drivers

    6.3.1 Ethernet Device Drivers

    • include/net/uip/uip-arch.h. All structures and APIs needed to work with Ethernet drivers are provided in this header file. The structure struct uip_driver_s defines the interface and is passed to uIP via netdev_register().
    • int netdev_register(FAR struct uip_driver_s *dev);. Each Ethernet driver registers itself by calling netdev_register().
    • Examples: drivers/net/dm90x0.c, arch/drivers/arm/src/c5471/c5471_ethernet.c, arch/z80/src/ez80/ez80_emac.c, etc.

    6.3.2 SPI Device Drivers

    • include/nuttx/spi.h. All structures and APIs needed to work with SPI drivers are provided in this header file.
    • struct spi_ops_s. Each SPI device driver must implement an instance of struct spi_ops_s. That structure defines a call table with the following methods:

        void lock(FAR struct spi_dev_s *dev);

        void select(FAR struct spi_dev_s *dev, enum spi_dev_e devid, boolean selected);
        uint32 setfrequency(FAR struct spi_dev_s *dev, uint32 frequency);
        void setmode(FAR struct spi_dev_s *dev, enum spi_mode_e mode);
        void setbits(FAR struct spi_dev_s *dev, int nbits);
        ubyte status(FAR struct spi_dev_s *dev, enum spi_dev_e devid);
        uint16 send(FAR struct spi_dev_s *dev, uint16 wd);
        void exchange(FAR struct spi_dev_s *dev, FAR const void *txbuffer, FAR void *rxbuffer, size_t nwords);

        int registercallback(FAR struct spi_dev_s *dev, mediachange_t callback, void *arg);

    • Binding SPI Drivers. SPI drivers are not normally directly accessed by user code, but are usually bound to another, higher level device driver. See for example, int mmcsd_spislotinitialize(int minor, int slotno, FAR struct spi_dev_s *spi) in drivers/mmcsd/mmcsd_spi.c. In general, the binding sequence is:
      • Get an instance of struct spi_dev_s from the hardware-specific SPI device driver, and
      • Provide that instance to the initialization method of the higher level device driver.
    • Examples: drivers/loop.c, drivers/mmcsd/mmcsd_spi.c, drivers/ramdisk.c, etc.

    6.3.3 I2C Device Drivers

    • include/nuttx/i2c.h. All structures and APIs needed to work with I2C drivers are provided in this header file.
    • struct i2c_ops_s. Each I2C device driver must implement an instance of struct i2c_ops_s. That structure defines a call table with the following methods:

        uint32 setfrequency(FAR struct i2c_dev_s *dev, uint32 frequency);
        int setaddress(FAR struct i2c_dev_s *dev, int addr, int nbits);
        int write(FAR struct i2c_dev_s *dev, const ubyte *buffer, int buflen);
        int read(FAR struct i2c_dev_s *dev, ubyte *buffer, int buflen);

    • Binding I2C Drivers. I2C drivers are not normally directly accessed by user code, but are usually bound to another, higher level device driver. In general, the binding sequence is:
      • Get an instance of struct i2c_dev_s from the hardware-specific I2C device driver, and
      • Provide that instance to the initialization method of the higher level device driver.
    • Examples: arch/z80/src/ez80/ez80_i2c.c, arch/z80/src/z8/z8_i2c.c, etc.

    6.3.4 Serial Device Drivers

    • include/nuttx/serial.h. All structures and APIs needed to work with serial drivers are provided in this header file.
    • struct uart_ops_s. Each serial device driver must implement an instance of struct uart_ops_s. That structure defines a call table with the following methods:

        int setup(FAR struct uart_dev_s *dev);
        void shutdown(FAR struct uart_dev_s *dev);
        int attach(FAR struct uart_dev_s *dev);
        void detach(FAR struct uart_dev_s *dev);
        int ioctl(FAR struct file *filep, int cmd, unsigned long arg);
        int receive(FAR struct uart_dev_s *dev, unsigned int *status);
        void rxint(FAR struct uart_dev_s *dev, boolean enable);
        boolean rxavailable(FAR struct uart_dev_s *dev);
        void send(FAR struct uart_dev_s *dev, int ch);
        void txint(FAR struct uart_dev_s *dev, boolean enable);
        boolean txready(FAR struct uart_dev_s *dev);
        boolean txempty(FAR struct uart_dev_s *dev);

    • int uart_register(FAR const char *path, FAR uart_dev_t *dev);. A serial driver may register itself by calling uart_register(), passing it the path where it will appear in the pseudo-file-system and it's initialized instance of struct uart_ops_s. By convention, serial device drivers are registered at paths like /dev/ttyS0, /dev/ttyS1, etc. See the uart_register() implementation in drivers/serial.c.
    • User Access. Serial drivers are, ultimately, normal character drivers and are accessed as other character drivers.
    • Examples: arch/arm/src/chip/lm3s_serial.c, arch/arm/src/lpc214x/lpc214x_serial.c, arch/z16/src/z16f/z16f_serial.c, etc.

    6.3.5 Frame Buffer Drivers

    • include/nuttx/fb.h. All structures and APIs needed to work with serial drivers are provided in this header file.
    • struct fb_vtable_s. Each frame buffer device driver must implement an instance of struct fb_vtable_s. That structure defines a call table with the following methods:

      Get information about the video controller configuration and the configuration of each color plane.

        int (*getvideoinfo)(FAR struct fb_vtable_s *vtable, FAR struct fb_videoinfo_s *vinfo);
        int (*getplaneinfo)(FAR struct fb_vtable_s *vtable, int planeno, FAR struct fb_planeinfo_s *pinfo);

      The following are provided only if the video hardware supports RGB color mapping:

      int (*getcmap)(FAR struct fb_vtable_s *vtable, FAR struct fb_cmap_s *cmap);
      int (*putcmap)(FAR struct fb_vtable_s *vtable, FAR const struct fb_cmap_s *cmap);

    The following are provided only if the video hardware supports a hardware cursor:

      int (*getcursor)(FAR struct fb_vtable_s *vtable, FAR struct fb_cursorattrib_s *attrib);
      int (*setcursor)(FAR struct fb_vtable_s *vtable, FAR struct fb_setcursor_s *settings);

  • Binding Frame Buffer Drivers. Frame buffer drivers are not normally directly accessed by user code, but are usually bound to another, higher level device driver. In general, the binding sequence is:
    • Get an instance of struct fb_vtable_s from the hardware-specific frame buffer device driver, and
    • Provide that instance to the initialization method of the higher level device driver.
  • Examples: arch/sim/src/up_framebuffer.c. See also the usage of the frame buffer driver in the graphics/ directory.

    • 6.3.6 Memory Technology Device Drivers

    • include/nuttx/mtd.h. All structures and APIs needed to work with serial drivers are provided in this header file.
    • struct mtd_dev_s. Each MTD device driver must implement an instance of struct mtd_dev_s. That structure defines a call table with the following methods:

      Erase the specified erase blocks (units are erase blocks):

        int (*erase)(FAR struct mtd_dev_s *dev, off_t startblock, size_t nblocks);

      Read/write from the specified read/write blocks:

      ssize_t (*bread)(FAR struct mtd_dev_s *dev, off_t startblock, size_t nblocks, FAR ubyte *buffer);
      ssize_t (*bwrite)(FAR struct mtd_dev_s *dev, off_t startblock, size_t nblocks, FAR const ubyte *buffer);

    Some devices may support byte oriented reads (optional). Most MTD devices are inherently block oriented so byte-oriented writing is not supported. It is recommended that low-level drivers not support read() if it requires buffering.

      ssize_t (*read)(FAR struct mtd_dev_s *dev, off_t offset, size_t nbytes, FAR ubyte *buffer);

    Support other, less frequently used commands:

    • MTDIOC_GEOMETRY: Get MTD geometry
    • MTDIOC_XIPBASE:: Convert block to physical address for eXecute-In-Place
    • MTDIOC_BULKERASE: Erase the entire device

    is provided via a sinble ioctl method (see include/nuttx/ioctl.h):

      int (*ioctl)(FAR struct mtd_dev_s *dev, int cmd, unsigned long arg);

  • Binding MTD Drivers. MTD drivers are not normally directly accessed by user code, but are usually bound to another, higher level device driver. In general, the binding sequence is:
    • Get an instance of struct mtd_dev_s from the hardware-specific MTD device driver, and
    • Provide that instance to the initialization method of the higher level device driver.
  • Examples: drivers/mtd/m25px.c and drivers/mtd/ftl.c

    • 6.3.7 SDIO Device Drivers

    • include/nuttx/sdio.h. All structures and APIs needed to work with serial drivers are provided in this header file.
    • struct sdio_dev_s. Each MTD device driver must implement an instance of struct sdio_dev_s. That structure defines a call table with the following methods:

      Initialization/setup:

        void (*reset)(FAR struct sdio_dev_s *dev);
        ubyte (*status)(FAR struct sdio_dev_s *dev);
        void (*widebus)(FAR struct sdio_dev_s *dev, boolean enable);
        void (*clock)(FAR struct sdio_dev_s *dev, enum sdio_clock_e rate);
        int (*attach)(FAR struct sdio_dev_s *dev);

      Command/Status/Data Transfer:

      void (*sendcmd)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 arg);
      int (*recvsetup)(FAR struct sdio_dev_s *dev, FAR ubyte *buffer, size_t nbytes);
      int (*sendsetup)(FAR struct sdio_dev_s *dev, FAR const ubyte *buffer, size_t nbytes);
      int (*cancel)(FAR struct sdio_dev_s *dev);
      int (*waitresponse)(FAR struct sdio_dev_s *dev, uint32 cmd);
      int (*recvR1)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 *R1);
      int (*recvR2)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 R2[4]);
      int (*recvR3)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 *R3);
      int (*recvR4)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 *R4);
      int (*recvR5)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 *R5);
      int (*recvR6)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 *R6);
      int (*recvR7)(FAR struct sdio_dev_s *dev, uint32 cmd, uint32 *R7);

    Event/Callback support:

      void (*waitenable)(FAR struct sdio_dev_s *dev, sdio_eventset_t eventset);
      sdio_eventset_t (*eventwait)(FAR struct sdio_dev_s *dev, uint32 timeout);
      void (*callbackenable)(FAR struct sdio_dev_s *dev, sdio_eventset_t eventset);
      int (*registercallback)(FAR struct sdio_dev_s *dev, worker_t callback, void *arg);

    DMA support:

      boolean (*dmasupported)(FAR struct sdio_dev_s *dev);
      int (*dmarecvsetup)(FAR struct sdio_dev_s *dev, FAR ubyte *buffer, size_t buflen);
      int (*dmasendsetup)(FAR struct sdio_dev_s *dev, FAR const ubyte *buffer, size_t buflen);

  • Binding SDIO Drivers. SDIO drivers are not normally directly accessed by user code, but are usually bound to another, higher level device driver. In general, the binding sequence is:
    • Get an instance of struct sdio_dev_s from the hardware-specific SDIO device driver, and
    • Provide that instance to the initialization method of the higher level device driver.
  • Examples: arch/arm/src/stm32/stm32_sdio.c and drivers/mmcsd/mmcsd_sdio.c

    • Appendix A: NuttX Configuration Settings

    The following variables are recognized by the build (you may also include architecture-specific settings).

    Architecture selection

    The following configuration items select the architecture, chip, and board configuration for the build.

    • CONFIG_ARCH: Identifies the arch subdirectory
    • CONFIG_ARCH_name: For use in C code
    • CONFIG_ARCH_CHIP: Identifies the arch/*/chip subdirectory
    • CONFIG_ARCH_CHIP_name: For use in C code
    • CONFIG_ARCH_BOARD: Identifies the configs subdirectory and hence, the board that supports the particular chip or SoC.
    • CONFIG_ARCH_BOARD_name: For use in C code
    • CONFIG_ENDIAN_BIG: Define if big endian (default is little endian).
    • CONFIG_ARCH_NOINTC: Define if the architecture does not support an interrupt controller or otherwise cannot support APIs like up_enable_irq() and up_disable_irq().
    • CONFIG_ARCH_IRQPRIO: Define if the architecture supports prioritization of interrupts and the up_prioritize_irq() API.

    Some architectures require a description of the RAM configuration:

    • CONFIG_DRAM_SIZE: Describes the installed DRAM.
    • CONFIG_DRAM_START: The start address of DRAM (physical)
    • CONFIG_DRAM_VSTART: The start address of DRAM (virtual)

    General build options:

    • CONFIG_RRLOAD_BINARY: Make the rrload binary format used with BSPs from ridgerun.com using the tools/mkimage.sh script.
    • CONFIG_INTELHEX_BINARY: Make the Intel HEX binary format used with many different loaders using the GNU objcopy program This option should not be selected if you are not using the GNU toolchain.
    • CONFIG_MOTOROLA_SREC: Make the Motorola S-Record binary format used with many different loaders using the GNU objcopy program Should not be selected if you are not using the GNU toolchain.
    • CONFIG_RAW_BINARY: Make a raw binary format file used with many different loaders using the GNU objcopy program. This option should not be selected if you are not using the GNU toolchain.
    • CONFIG_HAVE_LIBM: Toolchain supports libm.a
    • CONFIG_HAVE_CXX: Toolchain supports C++ and CXX, CXXFLAGS, and COMPILEXX have been defined in the configurations Make.defs file.

    General OS setup

    • CONFIG_EXAMPLE: identifies the subdirectory in examples that will be used in the build.
    • CONFIG_DEBUG: enables built-in debug options
    • CONFIG_DEBUG_VERBOSE: enables verbose debug output
    • CONFIG_DEBUG_SYMBOLS: build without optimization and with debug symbols (needed for use with a debugger).
    • CONFIG_DEBUG_SCHED: enable OS debug output (disabled by default)
    • CONFIG_DEBUG_MM: enable memory management debug output (disabled by default)
    • CONFIG_DEBUG_NET: enable network debug output (disabled by default)
    • CONFIG_DEBUG_USB: enable USB debug output (disabled by default)
    • CONFIG_DEBUG_FS: enable file system debug output (disabled by default)
    • CONFIG_DEBUG_LIB: enable C library debug output (disabled by default)
    • CONFIG_DEBUG_BINFMT: enable binary loader debug output (disabled by default)
    • CONFIG_DEBUG_GRAPHICS: enable NX graphics debug output (disabled by default)
    • CONFIG_ARCH_LOWPUTC: architecture supports low-level, boot time console output
    • CONFIG_MM_REGIONS: If the architecture includes multiple regions of memory to allocate from, this specifies the number of memory regions that the memory manager must handle and enables the API mm_addregion(start, end);
    • CONFIG_TICKS_PER_MSEC: The default system timer is 100Hz or TICKS_PER_MSEC=10. This setting may be defined to inform NuttX that the processor hardware is providing system timer interrupts at some interrupt interval other than 10 msec.
    • CONFIG_RR_INTERVAL: The round robin time slice will be set this number of milliseconds; Round robin scheduling can be disabled by setting this value to zero.
    • CONFIG_SCHED_INSTRUMENTATION: enables instrumentation in scheduler to monitor system performance
    • CONFIG_TASK_NAME_SIZE: Specifies that maximum size of a task name to save in the TCB. Useful if scheduler instrumentation is selected. Set to zero to disable.
    • CONFIG_START_YEAR, CONFIG_START_MONTH, CONFIG_START_DAY - Used to initialize the internal time logic.
    • CONFIG_GREGORIAN_TIME: Enables Gregorian time conversions. You would only need this if you are concerned about accurate time conversions in the recent past or in the distant future.
    • CONFIG_JULIAN_TIME: Enables Julian time conversions. You would only need this if you are concerned about accurate time conversion in the distand past. You must also define CONFIG_GREGORIAN_TIME in order to use Julian time.
    • CONFIG_DEV_CONSOLE: Set if architecture-specific logic provides /dev/console. Enables stdout, stderr, stdin.
    • CONFIG_MUTEX_TYPES: Set to enable support for recursive and errorcheck mutexes. Enables pthread_mutexattr_settype().
    • CONFIG_PRIORITY_INHERITANCE: Set to enable support for priority inheritance on mutexes and semaphores. Priority inheritance is a strategy of addressing priority inversion. Details of the NuttX implementation of priority inheritance is discussed elsewhere.
    • CONFIG_SEM_PREALLOCHOLDERS: This setting is only used if priority inheritance is enabled. It defines the maximum number of different threads (minus one) that can take counts on a semaphore with priority inheritance support. This may be set to zero if priority inheritance is disabled OR if you are only using semaphores as mutexes (only one holder) OR if no more than two threads participate using a counting semaphore.
    • CONFIG_SEM_NNESTPRIO: If priority inheritance is enabled, then this setting is the maximum number of higher priority threads (minus 1) than can be waiting for another thread to release a count on a semaphore. This value may be set to zero if no more than one thread is expected to wait for a semaphore.
    • CONFIG_FDCLONE_DISABLE: Disable cloning of all file descriptors by task_create() when a new task is started. If set, all files/drivers will appear to be closed in the new task.
    • CONFIG_FDCLONE_STDIO: Disable cloning of all but the first three file descriptors (stdin, stdout, stderr) by task_create() when a new task is started. If set, all files/drivers will appear to be closed in the new task except for stdin, stdout, and stderr.
    • CONFIG_SDCLONE_DISABLE: Disable cloning of all socket desciptors by task_create() when a new task is started. If set, all sockets will appear to be closed in the new task.
    • CONFIG_NXFLAT: Enable support for the NXFLAT binary format. This format will support execution of NuttX binaries located in a ROMFS filesystem (see examples/nxflat).
    • CONFIG_SCHED_WORKQUEUE: Create a dedicated "worker" thread to handle delayed processing from interrupt handlers. This feature is required for some drivers but, if there are not complaints, can be safely disabled. The worker thread also performs garbage collection -- completing any delayed memory deallocations from interrupt handlers. If the worker thread is disabled, then that clean will be performed by the IDLE thread instead (which runs at the lowest of priority and may not be appropriate if memory reclamation is of high priority). If CONFIG_SCHED_WORKQUEUE is enabled, then the following options can also be used:
    • CONFIG_SCHED_WORKPRIORITY: The execution priority of the worker thread. Default: 50
    • CONFIG_SCHED_WORKPERIOD: How often the worker thread checks for work in units of microseconds. Default: 50*1000 (50 MS).
    • CONFIG_SCHED_WORKSTACKSIZE: The stack size allocated for the worker thread. Default: CONFIG_IDLETHREAD_STACKSIZE.
    • CONFIG_SIG_SIGWORK: The signal number that will be used to wake-up the worker thread. Default: 4

    The following can be used to disable categories of APIs supported by the OS. If the compiler supports weak functions, then it should not be necessary to disable functions unless you want to restrict usage of those APIs.

    There are certain dependency relationships in these features.

    • mq_notify() logic depends on signals to awaken tasks waiting for queues to become full or empty.
    • pthread_condtimedwait() depends on signals to wake up waiting tasks.
      CONFIG_DISABLE_CLOCK, CONFI_DISABLE_POSIX_TIMERS, CONFIG_DISABLE_PTHREAD, CONFIG_DISABLE_SIGNALS, CONFIG_DISABLE_MQUEUE, CONFIG_DISABLE_MOUNTPOUNT

    Miscellaneous libc settings

    • CONFIG_NOPRINTF_FIELDWIDTH: sprintf-related logic is a little smaller if we do not support fieldwidthes

    Allow for architecture optimized implementations

    The architecture can provide optimized versions of the following to improve system performance.

      CONFIG_ARCH_MEMCPY, CONFIG_ARCH_MEMCMP, CONFIG_ARCH_MEMMOVE, CONFIG_ARCH_MEMSET, CONFIG_ARCH_STRCMP, CONFIG_ARCH_STRCPY, CONFIG_ARCH_STRNCPY, CONFIG_ARCH_STRLEN, CONFIG_ARCH_BZERO, CONFIG_ARCH_KMALLOC, CONFIG_ARCH_KZMALLOC, ONFIG_ARCH_KFREE,

    Sizes of configurable things (0 disables)

    • CONFIG_MAX_TASKS: The maximum number of simultaneously active tasks. This value must be a power of two.
    • CONFIG_NPTHREAD_KEYS: The number of items of thread- specific data that can be retained
    • CONFIG_NFILE_DESCRIPTORS: The maximum number of file descriptors (one for each open)
    • CONFIG_NFILE_STREAMS: The maximum number of streams that can be fopen'ed
    • CONFIG_NAME_MAX: The maximum size of a file name.
    • CONFIG_STDIO_BUFFER_SIZE: Size of the buffer to allocate on fopen. (Only if CONFIG_NFILE_STREAMS > 0)
    • CONFIG_NUNGET_CHARS: Number of characters that can be buffered by ungetc() (Only if CONFIG_NFILE_STREAMS > 0)
    • CONFIG_PREALLOC_MQ_MSGS: The number of pre-allocated message structures. The system manages a pool of preallocated message structures to minimize dynamic allocations
    • CONFIG_MQ_MAXMSGSIZE: Message structures are allocated with a fixed payload size given by this setting (does not include other message structure overhead.
    • CONFIG_PREALLOC_WDOGS: The number of pre-allocated watchdog structures. The system manages a pool of preallocated watchdog structures to minimize dynamic allocations
    • CONFIG_DEV_PIPE_SIZE: Size, in bytes, of the buffer to allocated for pipe and FIFO support (default is 1024).

    File Systems

    • CONFIG_FS_FAT: Enable FAT filesystem support.
    • CONFIG_FAT_SECTORSIZE: Max supported sector size.
    • CONFIG_FS_ROMFS: Enable ROMFS filesystem support

    SPI-based MMC/SD driver

    • CONFIG_MMCSD_NSLOTS: Number of MMC/SD slots supported by the driver. Default is one.
    • CONFIG_MMCSD_READONLY: Provide read-only access. Default is Read/Write
    • CONFIG_MMCSD_SPICLOCK: Maximum SPI clock to drive MMC/SD card. Default is 20MHz.

    SDIO-based MMC/SD driver

    • CONFIG_FS_READAHEAD: Enable read-ahead buffering
    • CONFIG_FS_WRITEBUFFER: Enable write buffering
    • CONFIG_SDIO_DMA: SDIO driver supports DMA
    • CONFIG_MMCSD_MMCSUPPORT: Enable support for MMC cards
    • CONFIG_MMCSD_HAVECARDDETECT: SDIO driver card detection is 100% accurate

    Network Support

    TCP/IP and UDP support via uIP

    • CONFIG_NET: Enable or disable all network features
    • CONFIG_NET_IPv6: Build in support for IPv6
    • CONFIG_NSOCKET_DESCRIPTORS: Maximum number of socket descriptors per task/thread.
    • CONFIG_NET_NACTIVESOCKETS: Maximum number of concurrent socket operations (recv, send, etc.). Default: CONFIG_NET_TCP_CONNS+CONFIG_NET_UDP_CONNS.
    • CONFIG_NET_SOCKOPTS: Enable or disable support for socket options.
    • CONFIG_NET_BUFSIZE: uIP buffer size
    • CONFIG_NET_TCP: TCP support on or off
    • CONFIG_NET_TCP_CONNS: Maximum number of TCP connections (all tasks).
    • CONFIG_NET_TCPBACKLOG: Incoming connections pend in a backlog until accept() is called. The size of the backlog is selected when listen() is called.
    • CONFIG_NET_TCP_READAHEAD_BUFSIZE: Size of TCP read-ahead buffers
    • CONFIG_NET_NTCP_READAHEAD_BUFFERS: Number of TCP read-ahead buffers (may be zero)
    • CONFIG_NET_MAX_LISTENPORTS: Maximum number of listening TCP ports (all tasks).
    • CONFIG_NET_TCPURGDATA: Determines if support for TCP urgent data notification should be compiled in. Urgent data (out-of-band data) is a rarely used TCP feature that is very seldom would be required.
    • CONFIG_NET_UDP: UDP support on or off
    • CONFIG_NET_UDP_CHECKSUMS: UDP checksums on or off
    • CONFIG_NET_UDP_CONNS: The maximum amount of concurrent UDP connections
    • CONFIG_NET_ICMP: Enable minimal ICMP support. Includes built-in support for sending replies to received ECHO (ping) requests.
    • CONFIG_NET_ICMP_PING: Provide interfaces to support application level support for sending ECHO (ping) requests and associating ECHO replies.
    • CONFIG_NET_PINGADDRCONF: Use "ping" packet for setting IP address
    • CONFIG_NET_STATISTICS: uIP statistics on or off
    • CONFIG_NET_RECEIVE_WINDOW: The size of the advertised receiver's window
    • CONFIG_NET_ARPTAB_SIZE: The size of the ARP table
    • CONFIG_NET_BROADCAST: Incoming UDP broadcast support
    • CONFIG_NET_MULTICAST: Outgoing multi-cast address support
    • CONFIG_NET_LLH_LEN: The link level header length
    • CONFIG_NET_FWCACHE_SIZE: number of packets to remember when looking for duplicates

    UIP Network Utilities

    • CONFIG_NET_DHCP_LIGHT: Reduces size of DHCP
    • CONFIG_NET_RESOLV_ENTRIES: Number of resolver entries

    THTTPD

    • CONFIG_THTTPD_PORT: THTTPD Server port number
    • CONFIG_THTTPD_IPADDR: Server IP address (no host name)
    • CONFIG_THTTPD_SERVER_ADDRESS: SERVER_ADDRESS: response
    • CONFIG_THTTPD_SERVER_SOFTWARE: SERVER_SOFTWARE: response
    • CONFIG_THTTPD_PATH: Server working directory. Default: /mnt/www.
    • CONFIG_THTTPD_CGI_PATH: Path to CGI executables. Default: /mnt/www/cgi-bin.
    • CONFIG_THTTPD_CGI_PATTERN: Only CGI programs whose expanded paths match this pattern will be executed. In fact, if this value is not defined then no CGI logic will be built. Default: /mnt/www/cgi-bin/*.
    • CONFIG_THTTPD_CGI_PRIORITY: Provides the priority of CGI child tasks
    • CONFIG_THTTPD_CGI_STACKSIZE: Provides the initial stack size of CGI child task (will be overridden by the stack size in the NXFLAT header)
    • CONFIG_THTTPD_CGI_BYTECOUNT: Byte output limit for CGI tasks.
    • CONFIG_THTTPD_CGI_TIMELIMIT: How many seconds to allow CGI programs to run before killing them.
    • CONFIG_THTTPD_CHARSET: The default character set name to use with text MIME types.
    • CONFIG_THTTPD_IOBUFFERSIZE:
    • CONFIG_THTTPD_INDEX_NAMES: A list of index filenames to check. The files are searched for in this order.
    • CONFIG_AUTH_FILE: The file to use for authentication. If this is defined then thttpd checks for this file in the local directory before every fetch. If the file exists then authentication is done, otherwise the fetch proceeds as usual. If you leave this undefined then thttpd will not implement authentication at all and will not check for auth files, which saves a bit of CPU time. A typical value is ".htpasswd&quout;
    • CONFIG_THTTPD_LISTEN_BACKLOG: The listen() backlog queue length.
    • CONFIG_THTTPD_LINGER_MSEC: How many milliseconds to leave a connection open while doing a lingering close.
    • CONFIG_THTTPD_OCCASIONAL_MSEC: How often to run the occasional cleanup job.
    • CONFIG_THTTPD_IDLE_READ_LIMIT_SEC: How many seconds to allow for reading the initial request on a new connection.
    • CONFIG_THTTPD_IDLE_SEND_LIMIT_SEC: How many seconds before an idle connection gets closed.
    • CONFIG_THTTPD_TILDE_MAP1 and CONFIG_THTTPD_TILDE_MAP2: Tilde mapping. Many URLs use ~username to indicate a user's home directory. thttpd provides two options for mapping this construct to an actual filename.
      1. Map ~username to <prefix>/username. This is the recommended choice. Each user gets a subdirectory in the main web tree, and the tilde construct points there. The prefix could be something like "users", or it could be empty.
      2. Map ~username to <user's homedir>/<postfix>. The postfix would be the name of a subdirectory off of the user's actual home dir, something like "public_html".
      You can also leave both options undefined, and thttpd will not do anything special about tildes. Enabling both options is an error. Typical values, if they're defined, are "users" for CONFIG_THTTPD_TILDE_MAP1 and "public_html" forCONFIG_THTTPD_TILDE_MAP2.
    • CONFIG_THTTPD_GENERATE_INDICES
    • CONFIG_THTTPD_URLPATTERN: If defined, then it will be used to match and verify referrers.

    USB Device-Side Support

    USB Device Controller Driver

    • CONFIG_USBDEV: Enables USB device support
    • CONFIG_USBDEV_ISOCHRONOUS: Build in extra support for isochronous endpoints
    • CONFIG_USBDEV_DUALSPEED: Hardware handles high and full speed operation (USB 2.0)
    • CONFIG_USBDEV_SELFPOWERED: Will cause USB features to indicate that the device is self-powered
    • CONFIG_USBDEV_MAXPOWER: Maximum power consumption in mA
    • CONFIG_USBDEV_TRACE: Enables USB tracing for debug
    • CONFIG_USBDEV_TRACE_NRECORDS: Number of trace entries to remember

    USB Serial Device Class Driver

    • CONFIG_USBSER: Enable compilation of the USB serial driver
    • CONFIG_USBSER_EPINTIN: The logical 7-bit address of a hardware endpoint that supports interrupt IN operation
    • CONFIG_USBSER_EPBULKOUT: The logical 7-bit address of a hardware endpoint that supports bulk OUT operation
    • CONFIG_USBSER_EPBULKIN: The logical 7-bit address of a hardware endpoint that supports bulk IN operation
    • CONFIG_USBSER_NWRREQS and CONFIG_USBSER_NRDREQS: The number of write/read requests that can be in flight
    • CONFIG_USBSER_VENDORID and CONFIG_USBSER_VENDORSTR: The vendor ID code/string
    • CONFIG_USBSER_PRODUCTID and CONFIG_USBSER_PRODUCTSTR: The product ID code/string
    • CONFIG_USBSER_RXBUFSIZE and CONFIG_USBSER_TXBUFSIZE: Size of the serial receive/transmit buffers

    USB Storage Device Configuration

    • CONFIG_USBSTRG: Enable compilation of the USB storage driver
    • CONFIG_USBSTRG_EP0MAXPACKET: Max packet size for endpoint 0
    • CONFIG_USBSTRGEPBULKOUT and CONFIG_USBSTRG_EPBULKIN: The logical 7-bit address of a hardware endpoints that support bulk OUT and IN operations
    • CONFIG_USBSTRG_NWRREQS and CONFIG_USBSTRG_NRDREQS: The number of write/read requests that can be in flight
    • CONFIG_USBSTRG_BULKINREQLEN and CONFIG_USBSTRG_BULKOUTREQLEN: The size of the buffer in each write/read request. This value needs to be at least as large as the endpoint maxpacket and ideally as large as a block device sector.
    • CONFIG_USBSTRG_VENDORID and CONFIG_USBSTRG_VENDORSTR: The vendor ID code/string
    • CONFIG_USBSTRG_PRODUCTID and CONFIG_USBSTRG_PRODUCTSTR: The product ID code/string
    • CONFIG_USBSTRG_REMOVABLE: Select if the media is removable

    Graphics related configuration settings

    • CONFIG_NX Enables overall support for graphics library and NX

    NX configuration setting

    • CONFIG_NX_MULTIUSER: Configures NX in multi-user mode.
    • CONFIG_NX_NPLANES: Some YUV color formats requires support for multiple planes, one for each color component. Unless you have such special hardware, this value should be undefined or set to 1.
    • CONFIG_NX_DISABLE_1BPP, CONFIG_NX_DISABLE_2BPP, CONFIG_NX_DISABLE_4BPP, CONFIG_NX_DISABLE_8BPP CONFIG_NX_DISABLE_16BPP, CONFIG_NX_DISABLE_24BPP, and CONFIG_NX_DISABLE_32BPP: NX supports a variety of pixel depths. You can save some memory by disabling support for unused color depths.
    • CONFIG_NX_PACKEDMSFIRST: If a pixel depth of less than 8-bits is used, then NX needs to know if the pixels pack from the MS to LS or from LS to MS
    • CONFIG_NX_MOUSE: Build in support for mouse input.
    • CONFIG_NX_KBD: Build in support of keypad/keyboard input.
    • CONFIG_NXTK_BORDERWIDTH: Specifies with with of the border (in pixels) used with framed windows. The default is 4.
    • CONFIG_NXTK_BORDERCOLOR1 and CONFIG_NXTK_BORDERCOLOR2: Specify the colors of the border used with framed windows. CONFIG_NXTK_BORDERCOLOR2 is the shadow side color and so is normally darker. The default is medium and dark grey, respectively
    • CONFIG_NXTK_AUTORAISE: If set, a window will be raised to the top if the mouse position is over a visible portion of the window. Default: A mouse button must be clicked over a visible portion of the window.
    • CONFIG_NXFONTS_CHARBITS: The number of bits in the character set. Current options are only 7 and 8. The default is 7.
    • CONFIG_NXFONT_SANS: At present, there is only one font. But if there were were more, then this option would select the sans serif font.

    NX Multi-user only options

    • CONFIG_NX_BLOCKING Open the client message queues in blocking mode. In this case, nx_eventhandler() will not return until a message is received and processed.
    • CONFIG_NX_MXSERVERMSGS and CONFIG_NX_MXCLIENTMSGS Specifies the maximum number of messages that can fit in the message queues. No additional resources are allocated, but this can be set to prevent flooding of the client or server with too many messages (CONFIG_PREALLOC_MQ_MSGS controls how many messages are pre-allocated).

    Stack and heap information

    • CONFIG_BOOT_RUNFROMFLASH: Some configurations support XIP operation from FLASH but must copy initialized .data sections to RAM.
    • CONFIG_BOOT_COPYTORAM: Some configurations boot in FLASH but copy themselves entirely into RAM for better performance.
    • CONFIG_STACK_POINTER: The initial stack pointer
    • CONFIG_IDLETHREAD_STACKSIZE: The size of the initial stack. This is the thread that (1) performs the initial boot of the system up to the point where user_start() is spawned, and (2) there after is the IDLE thread that executes only when there is no other thread ready to run.
    • CONFIG_USERMAIN_STACKSIZE: The size of the stack to allocate for the main user thread that begins at the user_start() entry point.
    • CONFIG_PTHREAD_STACK_MIN: Minimum pthread stack size
    • CONFIG_PTHREAD_STACK_DEFAULT: Default pthread stack size
    • CONFIG_HEAP_BASE: The beginning of the heap
    • CONFIG_HEAP_SIZE: The size of the heap

    Appendix B: Trademarks
  • ARM, ARM7 ARM7TDMI, ARM9, ARM920T, ARM926EJS, Cortex-M3 are trademarks of Advanced RISC Machines, Limited.
  • Cygwin is a trademark of Red Hat, Incorporated.
  • Linux is a registered trademark of Linus Torvalds.
  • Eagle-100 is a trademark of Micromint USA, LLC.
  • LPC2148 is a trademark of NXP Semiconductors.
  • TI is a trade name of Texas Instruments Incorporated.
  • UNIX is a registered trademark of The Open Group.
  • VxWorks is a registered trademark of Wind River Systems, Incorporated.
  • ZDS, ZNEO, Z16F, Z80, and Zilog are a registered trademark of Zilog, Inc.

    • NOTE: NuttX is not licensed to use the POSIX trademark. NuttX uses the POSIX standard as a development guideline only.