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[libcpu][riscv] add a doc for wch saving the irq stack as stack-512 #10063

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Merged
supperthomas merged 1 commit into from
Mar 3, 2025
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[libcpu][riscv] add a doc for wch saving the irq stack as stack-512 #10063

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9 changes: 9 additions & 0 deletions libcpu/risc-v/common/context_gcc.S
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,15 @@ rt_hw_interrupt_enable:
rt_hw_context_switch_to:
la t0, __rt_rvstack
#ifdef SOC_RISCV_FAMILY_CH32
/*
* if it is an assembly entry code, the SP offset value is determined by the assembly code,
* but the C code is determined by the compiler, so we subtract 512 here as a reservation.
* When entering the interrupt function of C code, the compiler automatically presses the stack
* into the task stack. We can only change the SP value used by the calling function after switching
* the interrupt stack.This problem can be solved by modifying the interrupt to the assembly entry,
* and there is no need to reserve 512 bytes. You only need to switch the interrupt stack at the
* beginning of the interrupt function
*/
addi t0, t0, -512 // for ch32
#endif /* SOC_RISCV_FAMILY_CH32 */
csrw mscratch,t0
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