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:

<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

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 toplevel 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 futher 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 futher 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 developement. 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: Work has just began on this port.
• 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(verfied 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.

2.4 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)

2.5 examples

Example and test programs to build against.

2.6 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)

2.7 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)

2.8 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)

2.9 lib

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

2.10 mm

This is the NuttX memory manager.

2.11 net

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

2.12 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)

2.13 sched

The files forming core of the NuttX RTOS reside here.

2.14 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

2.15 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.

3.1 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 targers, 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.

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 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:

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

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);
#endf

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);
#endf

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 achitecture- specific logic in order to dispaly 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 alphnumeric 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.

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

Pseudo Root File System. Or, a simple in-memory, psuedo 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 psuedo file system (in the same sense that the Linux /proc file system is also referred to as a psuedo file system).

Any user supplied data or logic can be accessed via the psuedo-file system. Built in support is provided for character and block drivers in the /dev psuedo 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 psuedo file system and to a 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 psuedo file system and true file systems may be mounted in the psuedo file system. In the typical Linux installation by comparison, the Linux root file system is a true file system and psuedo 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.

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).
• 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 suports prioritizaton 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 hould 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: mmke 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 configuratins 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_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 file system debug output (disabled by default)
• CONFIG_DEBUG_LIB: enable C library 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 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.
• 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 addessing 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.