一、任务切换#
PendSV_Handler CPSID I ; Cortex-M7 errata notice. See Note #5 MOV32 R2, OS_KA_BASEPRI_Boundary ; Set BASEPRI priority level required for exception preemption LDR R1, [R2] MSR BASEPRI, R1 DSB ISB CPSIE I
MRS R0, PSP ; PSP is process stack pointer STMFD R0!, {R4-R11, R14} ; Save remaining regs r4-11, R14 on process stack
LDR R5, =OSTCBCur ; OSTCBCur->OSTCBStkPtr = SP; LDR R1, [R5] STR R0, [R1] ; R0 is SP of process being switched out
; At this point, entire context of process has been saved MOV R4, LR ; Save LR exc_return value BL OSTaskSwHook ; Call OSTaskSwHook() for FPU Push & Pop
LDR R0, =OSPrioCur ; OSPrioCur = OSPrioHighRdy; LDR R1, =OSPrioHighRdy LDRB R2, [R1] STRB R2, [R0]
LDR R1, =OSTCBHighRdy ; OSTCBCur = OSTCBHighRdy; LDR R2, [R1] STR R2, [R5]
ORR LR, R4, #0x04 ; Ensure exception return uses process stack LDR R0, [R2] ; R0 is new process SP; SP = OSTCBHighRdy->OSTCBStkPtr; LDMFD R0!, {R4-R11, R14} ; Restore r4-11, R14 from new process stack MSR PSP, R0 ; Load PSP with new process SP
MOV32 R2, #0 ; Restore BASEPRI priority level to 0 CPSID I MSR BASEPRI, R2 DSB ISB CPSIE I BX LR ; Exception return will restore remaining context
ALIGN ; Removes warning[A1581W]: added <no_padbytes> of padding at <address>
END-
触发PendSV的中断，进入中断服务程序。
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屏蔽低优先级的中断，或者直接关闭中断。关中断防止额外的中断嵌套。
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使用MRS指令读取PSP指针的值。因为CPU进入了中断模式，SP指针已经变成了MSP，所以不能直接压栈，只能通过MRS指令读取PSP的值，再将R4到R11和R14寄存器的值直接压栈进入PSP。
为什么不保存其他寄存器的值？