Under Construction

NuttX Operating System

Porting Guide

by

Gregory Nutt

Last Update: March 26, 2007

Table of Contents

  • 1.0 1.0 Introduction
  • 2.0 Directory Structure
  • 3.0 Configuring and Building
  • 4.0 Architecture APIs

    • 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 archectures into the build.

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

    General Philosophy.

    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 sudirectory under arch/ containing logic specific to the new architecuture. 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

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

    2.3 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:

    2.3.2 Summary of Files

    2.3.2.1 Board Specific Logic

    2.3.2.2 Board Specific Configuration Files

    The configs/<board-name>/ sub-directory holds all of the files that are necessary to configure Nuttx for the particular board. The procedure for configuring NuttX is described below, This paragraph will describe the contents of these configuration files.

    2.3.3 Supported Boards

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

    * A customized version of the buildroot is available to build these toolchains.

    2.4 drivers

    This directory holds architecture-independent device drivers.

    2.5 examples

    Example and test programs to build against.

    2.6 fs

    This directory contains the NuttX filesystem. The NuttX filesystem is very simple; it does not involve any block drivers or particular filesystem (like FAT or EXT2 etc.). The NuttX filesystem simply supports a set a filesystem APIs (open(), close(), read(), write, etc.) and a registration mechanism that allows devices drivers to a associated with nodes in a file-system-like name space.

    2.7 include

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

    2.8 lib

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

    2.9 mm

    This is the NuttX memory manager.

    2.10 sched

    The files forming core of the NuttX RTOS reside here.

    2.11 tools

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

    2.12 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:

    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.

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

    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:

    The ${TOPDIR} directory holds:

    That directory also holds:

    The setenv.sh contains Linux 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:

    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 intial 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:

    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:

    This API is NOT required if CONFIG_CUSTOM_STACK is defined.

    Inputs:

    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:

    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:

    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:

    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 diable 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 'igdeliver' 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: void up_disable_irq(int irq);

    Description. Disable the IRQ specified by 'irq'

    4.1.17 up_enable_irq()

    Prototype: void up_enable_irq(int irq);

    Description. Enable the IRQ specified by 'irq'

    4.1.18 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

    This API is NOT required if CONFIG_HEAP_BASE is defined.

    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 achitecture- specific logic in order to dispaly an interrupt to the appropriate, registered handling logic.

    Appendix A: NuttX Configuration Settings

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

    Architecture selection

    General OS setup

    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.

    Miscellaneous libc settings

    Allow for architecture optimized implementations

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

    Sizes of configurable things (0 disables)

    Stack and heap information