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

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

  cd tools
  ./configure.sh <board-name>

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 targers, and
• The shell script setenv.sh that sets up the configuration environment for the build.

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:

• 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 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:

• 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:

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 taks, 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 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 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

The following configuration itemes 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).

Some architectures require a description of the the RAM configuration:

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

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_SCHED: enable OS debug output (disabled by default)
• CONFIG_DEBUG_MM: enable memory management debug output (disabld by default)
• CONFIG_DEBUG_NET: enable network debug output (disabled by default)
• CONFIG_DEBUG_FS: enable filesystem debug output (disabled by default)
• CONFIG_DEBUG_LIB: enable C library debug output (disabled by default)
• CONFIG_HAVE_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 timeslice 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: Spcifies 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_JULIAN_TIME: Enables Julian time conversions
• CONFIG_DEV_CONSOLE: Set if architecture-specific logic provides /dev/console. Enables stdout, stderr, stdin.