Hi.
I thought that if the test report 'SUCCESSFUL', it means that the function 'PORT SWITCH' okay.
When porting I guiding IAR documentation 'EWAVR_CompilerRefernce.pdf':
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Scratch registers
Any function is permitted to destroy the contents of a scratch register. If a function needs the register value after a call to another function, it must store it during the call, for example on the stack. For both calling conventions, these 14 registers can be used as scratch registers by a function:
R0-R3, R16-R23, and R30-R31
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Preserved registers
Preserved registers, on the other hand, are preserved across function calls. The called function can use the register for other purposes, but must save the value before using the register and restore it at the exit of the function. For both calling conventions, these registers are preserved registers:
R4-R15 and R24-R27
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Special registers
For some registers, you must consider certain prerequisites:
◠The stack pointer—register Y—must at all times point to the last element on the stack. In the eventuality of an interrupt, everything below the point the stack pointer points to, will be destroyed.
â— If using the -v4 or -v6 processor option, the RAMPY register is part of the data stack pointer.
â— If using a processor option which uses any of the registers EIND, RAMPX, or RAMPZ, these registers are treated as scratch registers.
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Register parameters
For both calling conventions, the registers available for passing parameters are:
R16–R23
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Interrupt functions
Interrupt functions differ from ordinary C functions in that:
â— Calls to interrupt functions are made via interrupt vectors; direct calls are not allowed
â— No arguments can be passed to an interrupt function
â— Interrupt functions return by using the RETI function.
At this moment I decided to use RSTACK (hardware stack pointed by SP register) to save context in 'port_switch' function. Also I had to determine the common size of the RSTACK for all threads.
Unfortunately I have not found a way to force the compiler to save all registers in the interrupts, and I hoped that compiler would do it itself - maybe it's my fault?
Another assumption is to use 'LARGE' or 'HUGE' memory model, because my board have 512kB external SRAM, and to have access to it compiler must use pointers larger then 16 bit (24 bit in that situation). That's why I used +7, +8 offset in structure intctx. Using direct constants in that case very danger, because environment depended. Is there any other way to do this?
Another problem is that hardware stack can be only in internal SRAM. Because all thread's stuff allocated in one chunk there are no way to use external memory for this.
There is a problem to allocate constants in FLASH. Though provided for this special word ROMCONST, it is not widely used, where possible, and a way of definition pointers to flash in IAR requires a different approach.
And of course the last problem is to make compiler independent HAL.
