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：

 

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