具体细节看那个切换函数。- OSPendSV
- IF OS_CRITICAL_INT_PRIO > 0 ; disable interupt 禁能中断
- MRS R3, BASEPRI
- LDR R1, =OS_CRITICAL_INT_PRIO
- MSR BASEPRI, R1
- ELSE
- MRS R3, PRIMASK
- CPSID I
- ENDIF
- MRS R0, PSP ; PSP is process stack pointer
- ; PSP是任务的堆栈指针
- CBZ R0, OSPendSV_nosave ; skip register save the first
- ; time第一次跳过保存
- SUB R0, R0, #0x20 ; save remaining regs r4-11 on
- ; process stack 保存r4-r11
- STM R0, {R4-R11}
- LDR R4, =OSTCBCur ; OSTCBCur->OSTCBStkPtr = SP;
- LDR R4, [R4]
- STR R0, [R4] ; R0 is SP of process being
- ; switched outR0是被切换开的任务
- ; 的堆栈指针
- OSPendSV_nosave
- PUSH {R14} ; need to save LR exc_return
- ; value保存LR返回值
- LDR R0, =OSTaskSwHook ; OSTaskSwHook();
- BLX R0
- POP {R14}
- LDR R4, =OSPrioCur ; OSPrioCur = OSPrioHighRdy
- LDR R5, =OSPrioHighRdy
- LDRB R6, [R5]
- STRB R6, [R4]
- LDR R4, =OSTCBCur ; OSTCBCur = OSTCBHighRdy;
- LDR R6, =OSTCBHighRdy
- LDR R6, [R6]
- STR R6, [R4]
- LDR R0, [R6] ; SP = OSTCBHighRdy->OSTCBStkPtr;
- LDM R0, {R4-R11} ; restore r4-11 from new process
- ; stack 从新任务的堆栈恢复r4-r11
- ADD R0, R0, #0x20
- MSR PSP, R0 ; load PSP with new process SP
- ; 从新任务的堆栈恢复PSP
- ORR LR, LR, #0x04 ; ensure exception return uses
- ; PSP确保返回后使用PSP
- IF OS_CRITICAL_INT_PRIO > 0 ; restore interrupts 恢复中断
- MSR BASEPRI, R3
- ELSE
- MSR PRIMASK, R3
- ENDIF
- BX LR ; exception return will restore
- ; remaining context
- ; 返回时会恢复剩下的上下文
- NOP
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