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author | gdisirio <gdisirio@35acf78f-673a-0410-8e92-d51de3d6d3f4> | 2009-01-17 20:15:19 +0000 |
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committer | gdisirio <gdisirio@35acf78f-673a-0410-8e92-d51de3d6d3f4> | 2009-01-17 20:15:19 +0000 |
commit | 350abc8106b440e3c09f40f7d76938079eab6ab1 (patch) | |
tree | 1f579e35c4abda53117c352d4d169432f76f9632 /ports | |
parent | d72f5d7b16daeec3c965bbbe4c81d4311b4d9df2 (diff) | |
download | ChibiOS-350abc8106b440e3c09f40f7d76938079eab6ab1.tar.gz ChibiOS-350abc8106b440e3c09f40f7d76938079eab6ab1.tar.bz2 ChibiOS-350abc8106b440e3c09f40f7d76938079eab6ab1.zip |
git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@628 35acf78f-673a-0410-8e92-d51de3d6d3f4
Diffstat (limited to 'ports')
-rw-r--r-- | ports/ARM7/port.dox | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/ports/ARM7/port.dox b/ports/ARM7/port.dox new file mode 100644 index 000000000..8b699febe --- /dev/null +++ b/ports/ARM7/port.dox @@ -0,0 +1,89 @@ +/**
+ * @defgroup ARM7 ARM7TDMI
+ * @{
+ * @section ARM7_NOTES The ARM7 port notes
+ * The ARM7 port supports three modes:
+ * - Pure ARM mode, this is the preferred mode for code speed. The code size
+ * is larger however. This mode is enabled when all the modules are compiled
+ * in ARM mode, see the Makefiles.
+ * - Pure THUMB mode, this is the preferred mode for code size. In this mode
+ * the execution speed is slower than the ARM mode. This mode is enabled
+ * when all the modules are compiled in THUMB mode, see the Makefiles.
+ * - Interworking mode, when in the system there are ARM modules mixed with
+ * THUMB modules then the interworking compiler option is enabled. This is
+ * usually the slowest mode and the code size is not as good as in pure
+ * THUMB mode.
+ *
+ * The ARM7 port makes some assumptions on the application code organization:
+ * - The @p main() function is invoked in system mode.
+ * - Each thread has a private user/system stack, the system has a single
+ * interrupt stack where all the interrupts are processed.
+ * - The threads are started in system mode.
+ * - The threads code can run in system mode or user mode, however the
+ * code running in user mode cannot invoke the ChibiOS/RT APIs directly
+ * because privileged instructions are used inside.<br>
+ * The kernel APIs can be eventually invoked by using a SWI entry point
+ * that handles the switch in system mode and the return in user mode.
+ * - Other modes are not preempt-able because the system code assumes the
+ * threads running in system mode. When running in supervisor or other
+ * modes make sure that the interrupts are globally disabled.
+ * - Interrupts nesting is not supported in the ARM7 code because their
+ * implementation, even if possible, is not really efficient in this
+ * architecture.
+ * - FIQ sources can preempt the kernel (by design) so it is not possible to
+ * invoke the kernel APIs from inside a FIQ handler. FIQ handlers are not
+ * affected by the kernel activity so there is not added jitter.
+ *
+ * @section ARM7_IH ARM7 Interrupt Handlers
+ * ARM7 Interrupt handlers do not save function-saved registers so you need to
+ * make sure your code saves them or does not use them (this happens
+ * because in the ARM7 port all the OS interrupt handler functions are declared
+ * naked).<br>
+ * Function-trashed registers (R0-R3,R12,LR,SR) are saved/restored by the
+ * system macros @p CH_IRQ_PROLOGUE() and @p CH_IRQ_EPILOGUE().<br>
+ * The easiest way to ensure this is to just invoke a function from within
+ * the interrupt handler, the function code will save all the required
+ * registers.<br>
+ * Example:
+ * @code
+ * CH_IRQ_HANDLER void irq_handler(void) {
+ * CH_IRQ_PROLOGUE();
+ *
+ * serve_interrupt();
+ *
+ * VICVectAddr = 0; // This is LPC214x-specific.
+ * CH_IRQ_EPILOGUE();
+ * }
+ * @endcode
+ * This is not a bug but an implementation choice, this solution allows to
+ * have interrupt handlers compiled in thumb mode without have to use an
+ * interworking mode (the mode switch is hidden in the macros), this
+ * greatly improves code efficiency and size. You can look at the serial
+ * driver for real examples of interrupt handlers.
+ *
+ * @ingroup Ports
+ */
+/** @} */
+
+/**
+ * @defgroup ARM7CONF Configuration Options
+ * @{
+ * @brief ARM7 specific configuration options.
+ * @details The ARM7 port allows some architecture-specific configurations
+ * settings that can be specified externally, as example on the compiler
+ * command line:
+ * - @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.<br>
+ * In practice this value is the stack space used by the chSchDoReschedule()
+ * stack frame.<br>
+ * This value can be affected by a variety of external things like compiler
+ * version, compiler options, kernel settings (speed/size) and so on.<br>
+ * The default for this value is @p 0x10 which should be a safe value, you
+ * can trim this down by defining the macro externally. This would save
+ * some valuable RAM space for each thread present in the system.<br>
+ * The default value is set into <b>./ports/ARM7/chcore.h</b>.
+ *
+ * @ingroup ARM7
+ */
+/** @} */
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