mayhem-firmware/firmware/chibios/os/ports/GCC/ARMCMx/port.dox

/*
    ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010,
                 2011,2012,2013 Giovanni Di Sirio.

    This file is part of ChibiOS/RT.

    ChibiOS/RT is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    ChibiOS/RT is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

                                      ---

    A special exception to the GPL can be applied should you wish to distribute
    a combined work that includes ChibiOS/RT, without being obliged to provide
    the source code for any proprietary components. See the file exception.txt
    for full details of how and when the exception can be applied.
*/

/**
 * @defgroup ARMCMx ARM Cortex-Mx
 * @details ARM Cortex-Mx port for the GCC compiler.
 *
 * @section ARMCMx_INTRO Introduction
 * This port supports all the cores implementing the ARMv6-M and ARMv7-M
 * architectures.
 *
 * @section ARMCMx_MODES Kernel Modes
 * The Cortex-Mx port supports two distinct kernel modes:
 * - <b>Advanced Kernel</b> mode. In this mode the kernel only masks
 *   interrupt sources with priorities below or equal to the
 *   @p CORTEX_BASEPRI_KERNEL level. Higher priorities are not affected by
 *   the kernel critical sections and can be used for fast interrupts.
 *   This mode is not available in the ARMv6-M architecture which does not
 *   support priority masking.
 * - <b>Compact Kernel</b> mode. In this mode the kernel handles IRQ priorities
 *   in a simplified way, all interrupt sources are disabled when the kernel
 *   enters into a critical zone and re-enabled on exit. This is simple and
 *   adequate for most applications, this mode results in a more compact and
 *   faster kernel.
 * .
 * The selection of the mode is performed using the port configuration option
 * @p CORTEX_SIMPLIFIED_PRIORITY. Apart from the different handling of
 * interrupts there are no other differences between the two modes. The
 * kernel API is exactly the same.
 *
 * @section ARMCMx_STATES_A System logical states in Compact Kernel mode
 * The ChibiOS/RT logical @ref system_states are mapped as follow in Compact
 * Kernel mode:
 * - <b>Init</b>. This state is represented by the startup code and the
 *   initialization code before @p chSysInit() is executed. It has not a
 *   special hardware state associated.
 * - <b>Normal</b>. This is the state the system has after executing
 *   @p chSysInit(). In this state interrupts are enabled. The processor
 *   is running in thread-privileged mode.
 * - <b>Suspended</b>. In this state the interrupt sources are globally
 *   disabled. The processor is running in thread-privileged mode. In this
 *   mode this state is not different from the <b>Disabled</b> state.
 * - <b>Disabled</b>. In this state the interrupt sources are globally
 *   disabled. The processor is running in thread-privileged mode. In this
 *   mode this state is not different from the <b>Suspended</b> state.
 * - <b>Sleep</b>. This state is entered with the execution of the specific
 *   instruction @p <b>wfi</b>.
 * - <b>S-Locked</b>. In this state the interrupt sources are globally
 *   disabled. The processor is running in thread-privileged mode.
 * - <b>I-Locked</b>. In this state the interrupt sources are globally
 *   disabled. The processor is running in exception-privileged mode.
 * - <b>Serving Regular Interrupt</b>. In this state the interrupt sources are
 *   not globally masked but only interrupts with higher priority can preempt
 *   the current handler. The processor is running in exception-privileged
 *   mode.
 * - <b>Serving Fast Interrupt</b>. Not implemented in compact kernel mode.
 * - <b>Serving Non-Maskable Interrupt</b>. The Cortex-Mx has a specific
 *   asynchronous NMI vector and several synchronous fault vectors that can
 *   be considered belonging to this category.
 * - <b>Halted</b>. Implemented as an infinite loop after globally masking all
 *   the maskable interrupt sources. The ARM state is whatever the processor
 *   was running when @p chSysHalt() was invoked.
 *
 * @section ARMCMx_STATES_B System logical states in Advanced Kernel mode
 * The ChibiOS/RT logical @ref system_states are mapped as follow in the
 * Advanced Kernel mode:
 * - <b>Init</b>. This state is represented by the startup code and the
 *   initialization code before @p chSysInit() is executed. It has not a
 *   special hardware state associated.
 * - <b>Normal</b>. This is the state the system has after executing
 *   @p chSysInit(). In this state the ARM Cortex-Mx has the BASEPRI register
 *   set at @p CORTEX_BASEPRI_USER level, interrupts are not masked. The
 *   processor is running in thread-privileged mode.
 * - <b>Suspended</b>. In this state the interrupt sources are not globally
 *   masked but the BASEPRI register is set to @p CORTEX_BASEPRI_KERNEL thus
 *   masking any interrupt source with lower or equal priority. The processor
 *   is running in thread-privileged mode.
 * - <b>Disabled</b>. Interrupt sources are globally masked. The processor
 *   is running in thread-privileged mode.
 * - <b>Sleep</b>. This state is entered with the execution of the specific
 *   instruction @p <b>wfi</b>.
 * - <b>S-Locked</b>. In this state the interrupt sources are not globally
 *   masked but the BASEPRI register is set to @p CORTEX_BASEPRI_KERNEL thus
 *   masking any interrupt source with lower or equal priority. The processor
 *   is running in thread-privileged mode.
 * - <b>I-Locked</b>. In this state the interrupt sources are not globally
 *   masked but the BASEPRI register is set to @p CORTEX_BASEPRI_KERNEL thus
 *   masking any interrupt source with lower or equal priority. The processor
 *   is running in exception-privileged mode.
 * - <b>Serving Regular Interrupt</b>. In this state the interrupt sources are
 *   not globally masked but only interrupts with higher priority can preempt
 *   the current handler. The processor is running in exception-privileged
 *   mode.
 * - <b>Serving Fast Interrupt</b>. Fast interrupts are defined as interrupt
 *   sources having higher priority level than the kernel
 *   (@p CORTEX_BASEPRI_KERNEL). In this state is not possible to switch to
 *   the I-Locked state because fast interrupts can preempt the kernel
 *   critical zone.<br>
 *   This state is not implemented in the ARMv6-M implementation because
 *   priority masking is not present in this architecture.
 * - <b>Serving Non-Maskable Interrupt</b>. The Cortex-Mx has a specific
 *   asynchronous NMI vector and several synchronous fault vectors that can
 *   be considered belonging to this category.
 * - <b>Halted</b>. Implemented as an infinite loop after globally masking all
 *   the maskable interrupt sources. The ARM state is whatever the processor
 *   was running when @p chSysHalt() was invoked.
 * .
 * @section ARMCMx_NOTES ARM Cortex-Mx/GCC port notes
 * The ARM Cortex-Mx port is organized as follow:
 * - The @p main() function is invoked in thread-privileged mode.
 * - Each thread has a private process stack, the system has a single main
 *   stack where all the interrupts and exceptions are processed.
 * - The threads are started in thread-privileged mode.
 * - Interrupt nesting and the other advanced core/NVIC features are supported.
 * - The Cortex-Mx port is perfectly generic, support for more devices can be
 *   easily added by adding a subdirectory under <tt>./os/ports/GCC/ARMCMx</tt>
 *   and giving it the name of the new device, then copy the files from another
 *   device into the new directory and customize them for the new device.
 * .
 * @ingroup gcc
 */

/**
 * @defgroup ARMCMx_CONF Configuration Options
 * @details ARM Cortex-Mx Configuration Options. The ARMCMx port allows some
 * architecture-specific configurations settings that can be overridden
 * by redefining them in @p chconf.h. Usually there is no need to change
 * the default values.
 * - @p INT_REQUIRED_STACK, this value represent the amount of stack space used
 *   by an interrupt handler between the @p extctx and @p intctx
 *   structures.
 * - @p IDLE_THREAD_STACK_SIZE, stack area size to be assigned to the IDLE
 *   thread. Usually there is no need to change this value unless inserting
 *   code in the IDLE thread using the @p IDLE_LOOP_HOOK hook macro.
 * - @p CORTEX_PRIORITY_SYSTICK, priority of the SYSTICK handler.
 * - @p CORTEX_PRIORITY_PENDSV, priority of the PENDSV handler.
 * - @p CORTEX_ENABLE_WFI_IDLE, if set to @p TRUE enables the use of the
 *   @p <b>wfi</b> instruction from within the idle loop. This option is
 *   defaulted to FALSE because it can create problems with some debuggers.
 *   Setting this option to TRUE reduces the system power requirements.
 * .
 * @section ARMCMx_CONF_1 ARMv6-M specific options
 * The following options are specific for the ARMv6-M architecture:
 * - @p CORTEX_ALTERNATE_SWITCH, when activated makes the OS use the PendSV
 *   exception instead of NMI as preemption handler.
 * .
 * @section ARMCMx_CONF_2 ARMv7-M specific options
 * The following options are specific for the ARMv6-M architecture:
 * - @p CORTEX_PRIORITY_SVCALL, priority of the SVCALL handler.
 * - @p CORTEX_SIMPLIFIED_PRIORITY, when enabled activates the Compact kernel
 *   mode.
 * .
 * @ingroup ARMCMx
 */

/**
 * @defgroup ARMCMx_CORE Core Port Implementation
 * @details ARM Cortex-Mx specific port code, structures and macros.
 *
 * @ingroup ARMCMx
 */

/**
 * @defgroup ARMCMx_V6M_CORE ARMv6-M Specific Implementation
 * @details ARMv6-M specific port code, structures and macros.
 *
 * @ingroup ARMCMx_CORE
 */

/**
 * @defgroup ARMCMx_V7M_CORE ARMv7-M Specific Implementation
 * @details ARMv7-M specific port code, structures and macros.
 *
 * @ingroup ARMCMx_CORE
 */

/**
 * @defgroup ARMCMx_STARTUP Startup Support
 * @details ChibiOS/RT provides its own generic startup file for the ARM
 * Cortex-Mx port.
 * Of course it is not mandatory to use it but care should be taken about the
 * startup phase details.
 *
 * @section ARMCMx_STARTUP_1 Startup Process
 * The startup process, as implemented, is the following:
 * -# Interrupts are masked globally.
 * -# The two stacks are initialized by assigning them the sizes defined in
 *    the linker script (also known as scatter file).
 * -# The CPU state is switched to Privileged and the PSP stack is used.
 * -# An early initialization routine @p __early_init() is invoked, if the
 *    symbol is not defined then an empty default routine is executed
 *    (weak symbol).
 * -# DATA and BSS segments are initialized.
 * -# Constructors are invoked.
 * -# The @p main() function is invoked with no parameters.
 * -# Destructors are invoked.
 * -# A branch is performed to the weak symbol @p _default_exit(). The
 *    default code is an endless empty loop.
 * .
 * @section ARMCMx_STARTUP_2 Expected linker symbols
 * The startup code starts at the symbol @p ResetHandler and expects the
 * following symbols to be defined in the linker script:
 * - @p __ram_end__, end of RAM.
 * - @p __main_stack_base__, main stack lower boundary.
 * - @p __main_stack_end__, main stack initial position.
 * - @p __process_stack_base__, process stack lower boundary.
 * - @p __process_stack_end__, process stack initial position.
 * - @p _textdata, address of the data segment source read only data.
 * - @p _data, start of the data segment.
 * - @p _edata, end of the data segment end location.
 * - @p _bss_start, start of the BSS.
 * - @p _bss_end, end of the BSS segment.
 * - @p __init_array_start, start of the constructors array.
 * - @p __init_array_end, end of the constructors array.
 * - @p __fini_array_start, start of the destructors array.
 * - @p __fini_array_end, end of the destructors array.
 * .
 * Additionally the kernel expects the following symbols:
 * - @p __main_thread_stack_base__, this symbol is required when the
 *   stack checking is enabled (<tt>CH_DBG_ENABLE_STACK_CHECK==TRUE</tt>),
 *   it is an alias of @p __process_stack_base__ in this port.
 * - @p __heap_base__ and @p __heap_end__, those symbols are required
 *   if the memory core manager is enabled (<tt>CH_USE_MEMCORE==TRUE</tt>)
 *   with a default core size set to zero (<tt>CH_MEMCORE_SIZE==0</tt>).
 * .
 * @ingroup ARMCMx
 */

/**
 * @defgroup ARMCMx_SPECIFIC Specific Implementations
 * @details Platform-specific port code.
 *
 * @ingroup ARMCMx
 */