STM32 ucosii 双堆栈初始化问题

菜鸟也想飞 · 发表于 2017-12-22 09:03:47

请大神帮忙解答一下为什么在OSStartHighRdy中MSP初始化的地址是OS_CPU_ExceptStkBase ；而PSP初始化地址是0？
OSStartHighRdy
LDR    R0, =NVIC_SYSPRI14                               ; 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

LDR    R0, =OS_CPU_ExceptStkBase                         ; Initialize the MSP to the OS_CPU_ExceptStkBase
LDR    R1, [R0]
MSR    MSP, R1

LDR    R0, =OSRunning                                     ; 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
B    OSStartHang

操作系统 · 发表于 2017-12-22 09:03:48

MSP 可以不用初始化.系统硬件自动搞定了.
PSP 初始化为0,是用来区别,是不是第一次切换任务,
因为第一次切换任务,无上一次任务来保存.不然,要保存上一个任务到栈.
PendSV_Handler
CPSID I          ; Prevent interruption during context switch
MRS    R0, PSP    ; PSP is process stack pointer
CBZ    R0, OS_CPU_PendSVHandler_nosave  ; Skip register save the first time 这里会判断 PSP 是不是0,是0直接跳到OS_CPU_PendSVHandler_nosave  执行.
  ;保存一下现场
SUBS R0, R0, #0x20 ; Save remaining regs r4-11 on process stack
STM    R0, {R4-R11}

LDR    R1, =OSTCBCur    ; OSTCBCur->OSTCBStkPtr = SP;
LDR    R1, [R1]
STR    R0, [R1]                                           ; R0 is SP of process being switched out

OS_CPU_PendSVHandler_nosave

LDR    R0, =OSTCBCur                                     ; OSTCBCur  = OSTCBHighRdy;
LDR    R1, =OSTCBHighRdy
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
CPSIE I
BX    LR                                                 ; Exception return will restore remaining context
   ALIGN
END