官方的例子不太好，不能中断嵌套，所有中断必须在同一优先级别，官方例子都是0，主要是在双堆栈指针使用上有问题
用下面两段代码替换就没问题了，也不存在原来有人说使用不同优化级别编译会死机的问题
OSStartHighRdy
LDR R0, =NVIC_SYSPRI2 ; Set the PendSV exception priority
LDR R1, =NVIC_PENDSV_PRI
STRB R1, [R0]
;MOVS R0, #0 ; Set the PSP to 0 for initial context switch call
;MSR PSP, R0
MRS R0, MSP
MSR PSP, R0
MRS R0, CONTROL
ORR R0, R0, #0x02
MSR CONTROL, R0
LDR R1, __OS_TCBCur
MRS R0, PSP
SUBS R0, R0, #0x24
STR R0, [R1]
LDR R0, __OS_Running ; OSRunning = TRUE
MOVS R1, #1
STRB R1, [R0]
LDR R0, =NVIC_INT_CTRL ; Trigger the PendSV exception (causes context switch)
LDR R1, =NVIC_PENDSVSET
STR R1, [R0]
CPSIE I ; Enable interrupts at processor level
OSStartHang
NOP
B OSStartHang ;Should never get here
OSPendSV
MRS R0, PSP ; PSP is process stack pointer
;CBZ R0, OSPendSV_nosave ; skip register save the first time
SUBS R0, R0, #0x20 ; save remaining regs r4-11 on process stack
STM R0, {R4-R11}
LDR R1, __OS_TCBCur ; OSTCBCur->OSTCBStkPtr = SP;
LDR R1, [R1]
STR R0, [R1] ; R0 is SP of process being switched out
; at this point, entire context of process has been saved
OSPendSV_nosave
PUSH {R14} ; need to save LR exc_return value
LDR R0, __OS_TaskSwHook ; OSTaskSwHook();
BLX R0
POP {R14}
LDR R0, __OS_PrioCur ; OSPrioCur = OSPrioHighRdy;
LDR R1, __OS_PrioHighRdy
LDRB R2, [R1]
STRB R2, [R0]
LDR R0, __OS_TCBCur ; OSTCBCur = OSTCBHighRdy;
LDR R1, __OS_TCBHighRdy
LDR R2, [R1]
STR R2, [R0]
LDR R0, [R2] ; R0 is new process SP; SP = OSTCBHighRdy->OSTCBStkPtr;
LDM R0, {R4-R11} ; restore r4-11 from new process stack
ADDS R0, R0, #0x20
MSR PSP, R0 ; load PSP with new process SP
;ORR LR, LR, #0x04 ; ensure exception return uses process stack
BX LR |
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