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各种硬件平台上的us OS移植实例(arm6)

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To build uC/OS:

1) You will need a C-Demon source directory, so that the C-Demon
   manifests and target architecture description files can be found.

2) Update the Makefile to reflect the architecture you are targetting.

3) make

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-- NOTEs ----------------------------------------------------------------------
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This release does not provide a full run-time system as required by
the ARM C compiler (i.e. __rt_sdiv10, etc.). It is assumed that the
user will link against the standard ARM library if they want such
support functions. However, using the current ARM library may result
in the initialisation from the library being used. This may cause
problems with C-Demon based systems due to some differences between it
and the old assembler Demon.

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The uC/OS world is very simple at the moment, and there is no support
for ARM aborts (prefetch or data), or any undefined instruction
support. It only provides basic tasking support.

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The uC/OS system *NEEDS* to provide its own IRQ and FIQ vector
handlers to deal with the magic of providing complete context
switches. To perform a context switch cleanly the interrupt code needs
to have access to *ALL* of the processor state at the instance of the
interrupt. It is not possible to use the C-Demon IRQ and FIQ vectoring
system, since uC/OS would then need to know about the workspace and
stack usage of the C-Demon system interrupts handlers to be able to
recover the complete processor state.

Unfortunately coding the main IRQ handler in C (using the __irq
extension) is not a viable option. Since we do not have access to the
initial stack pointer and register contents from C. The compiler will
have saved the registers it thinks it needs to, and will have created
a stack frame that we do not know the size of. To provide the handler
as a C routine we would need to use the __irq extension, which
precludes the use of a stack call frame. If we did build the world
with frame-pointer support, we would be able to decode the stack
usage. However such a scheme would be quite slow.

The best all round compromise is for the uC/OS environment to provide
its own, specific, system interrupt handlers.

These system handlers are attached and initialised as part of the
uC/OS OSStart function. To add ISRs for a particular target
architecture interrupt source requires that either
ARMInstallIRQHandler or ARMInstallFIQHandler be called to attach the
user supplied handler routine:

	#include "osdefs.h" /* uC/OS ARM interface */
	IRQHandlerFn prev ; /* holder for previous handler function */
	if ((prev = ARMInstallIRQHandler(bitpos,newISR)) == NULL)
	 SWI_Write0("Failed to attach IRQ handler\n") ;

NOTE: The attached ISR routines are executing with interrupts
disabled, so they should not call anything that may perform an
OS_EXIT_CRITICAL.

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