Comments (7)
rayc345
commented on June 25, 2024
Not manually, For Armv7-M ISA based CPU like Cortex-M7, caller save registers (r0-r3,r12,LR(r14),PC(r15), xPSR) would be saved into stack by hardware, and r4-r9, r10,r11,SP would be saved by callee functions, save and restore instructions would be generated by compilers, so for C programmers, no manual procedure is required to save/restore contexts.
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amgross
commented on June 25, 2024
Hi @rayc345
Threadx context save/restore not only saves register, but also manages the option that while the interrupt happened something that requires context switch. For this case stuff needed to be stored on the stack and context restore returns from the interrupt to the scheduler instead of to the original point where the interrupt was called from.
And hence I think the answer to @maxkunes is that indeed it should be called from assembly code.
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maxkunes
commented on June 25, 2024
@amgross Thank you for the reply.
Honestly, I've been working with ThreadX for 3 years now without doing this, and I've yet to see anything that is obviously wrong.
Can you explain what behavior might be seen in theory without these calls? Maybe I have some intermittent bugs due to this that I haven't connected to anything else.
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amgross
commented on June 25, 2024
Hi @maxkunes ,
By 'without doing it' you mean you call it from C code or not calling it at all?
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maxkunes
commented on June 25, 2024
I do not call it at all.
…On Sat, May 18, 2024 at 10:21 PM amgross ***@***.***> wrote:
Hi @maxkunes <https://github.com/maxkunes> ,
By 'without doing it' you mean you call it from C code or not calling it
at all?
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amgross
commented on June 25, 2024
Surprisingly (for me), it seems like I was mistaken and there is no need for cortex M to use save/restore
threadx/ports/cortex_m7/ac5/readme_threadx.txt
Lines 161 to 173 in 485a02f
So @rayc345 is correct
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maxkunes
commented on June 25, 2024
But that seems to depend on the compiler used?
See:
https://github.com/eclipse-threadx/threadx/blob/485a02faec6edccef14812ddce6844af1d7d2eef/ports/cortex_m7/gnu/readme_threadx.txt
Which says on GNU you have to use assembly to save r0 and lr and then you
can bl to your C function.
Im using arm-none-eabi-gcc, which presumably is AC5 or 6? If so, that
explains why I don't have issues.
…On Sun, May 19, 2024 at 2:33 AM amgross ***@***.***> wrote:
Surprisingly (for me), it seems like I was mistaken and there is no need
for cortex M to use save/restore
https://github.com/eclipse-threadx/threadx/blob/485a02faec6edccef14812ddce6844af1d7d2eef/ports/cortex_m7/ac5/readme_threadx.txt#L161-L173
So @rayc345 <https://github.com/rayc345> is correct
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Related Issues (20)
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- Dose threadx module has 'who am I' utility?
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- ULONG == uint32_t in 64-bit system cause problem HOT 1
- Fix CMake minimum require version warning
- vfp_enable breaks FileX on Cortex-R5 HOT 1
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- ThreadX Context Save/Restore of Floating Point Registers for Cortex-R5 HOT 2
- Consulting HOT 4
- support for hardware stack checking in ARC HS
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