ucOS-II基于ARM920T的OSCtxSw实现分析

基于ARM920T的OSCtxSw实现分析：

首先必须了解，在将ucos-II移植到ARM920T时，使用了如下结构的任务栈：

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程序清单：基于ARM920T的OSCtxSw实现分析

注意：ARM需手动保存pc和psw

OSCtxSw

; Special optimised code below:

；1、根据任务栈结构，分别压栈，保存旧任务的现场

stmfd sp!,{lr} ; push pc (lr should be pushed in place of PC)

stmfd sp!,{r0-r12,lr} ; push lr & register file

mrs r4,cpsr

stmfd sp!,{r4} ; push current psr

mrs r4,spsr

stmfd sp!,{r4} ; push current spsr

; 2、OSPrioCur = OSPrioHighRdy

ldr r4,=OSPrioCur

ldr r5,=OSPrioHighRdy

ldrb r6,[r5]

strb r6,[r4]

; 3、Get current task TCB address:r5= OSTCBCur

ldr r4,=OSTCBCur; r4 = &OSTCBCur

ldr r5,[r4]

；4、OSTCBCur->OSTCBStkPtr = SP;

str sp,[r5] ; store sp in preempted tasks's TCB

bl OSTaskSwHook ; call Task Switch Hook

; 5、Get highest priority task TCB address:r6= OSTCBHighRdy

ldr r6,=OSTCBHighRdy

ldr r6,[r6]

； 6、SP = OSTCBHighRdy ->OSTCBStkPtr;

ldr sp,[r6] ; get new task's stack pointer

; 7、OSTCBCur = OSTCBHighRdy

str r6,[r4] ; set new current task TCB address

；8、根据任务栈结构，分别出栈，恢复新任务的现场

ldmfd sp!,{r4} ; pop new task's spsr

msr SPSR_cxsf,r4

ldmfd sp!,{r4} ; pop new task's psr

msr CPSR_cxsf,r4

ldmfd sp!,{r0-r12,lr,pc} ; pop new task's r0-r12,lr & pc