3) 中断级任务切换函数
① 该函数由OSIntExit()和OSExIntExit()调用，它若在时钟中断ISR中发现有高优先级任务等特的时候信号到来，则需要在中断退出后并不返回被中断的，的而是直接调度就绪的高高优先级任务执行.这样做的目的主要是能够尽快的让优先级高的任务得到响应，进而保证系统的实时性。
OSIntCtxSw
LDR R0, OS_TaskSwHook ; OSTaskSwHook();
MOV LR, PC
BX R0
LDR R4, OS_PrioCur ; OSPrioCur = OSPrioHighRdy
LDR R5, OS_PrioHighRdy
LDRB R6,[R5]
STRB R6,[R4]
LDR R4,OS_TCBCur ; OSTCBCur = OSTCBHighRdy;
LDR R6,OS_TCBHighRdy
LDR R6,[R6]
STR R6,[R4]
LDR SP,[R6] ; SP = OSTCBHighRdy->OSTCBStkPtr;
; RESTORE NEW TASK'S CONTEXT
LDMFD SP!, {R4} ; Pop new task's CPSR
MSR SPSR_cxsf, R4
LDMFD SP!, {R0-R12,LR,PC}^ ; Pop new task's context
② 两种形式的中断程序
OS_CPU_IRQ_ISR
STMFD SP!, {R1-R3} ; PUSH WORKING REGISTERS ONTO IRQ STACK
MOV R1, SP ; Save IRQ stack pointer
ADD SP, SP,#12 ; Adjust IRQ stack pointer
SUB R2, LR,#4 ; Adjust PC for return address to task
MRS R3, SPSR ; Copy SPSR (i.e. interrupted task's CPSR) to R3
MSR CPSR_c, #(NO_INT | SVC32_MODE) ; Change to SVC mode
; SAVE TASK'S CONTEXT ONTO TASK'S STACK
STMFD SP!, {R2} ; Push task's Return PC
STMFD SP!, {LR} ; Push task's LR
STMFD SP!, {R4-R12} ; Push task's R12-R4
LDMFD R1!, {R4-R6} ; Move task's R1-R3 from IRQ stack to SVC stack
STMFD SP!, {R4-R6}
STMFD SP!, {R0} ; Push task's R0 onto task's stack
STMFD SP!, {R3} ; Push task's CPSR (i.e. IRQ's SPSR)
LDR R0, OS_IntNesting ; OSIntNesting++;
LDRB R1, [R0]
ADD R1, R1,#1
STRB R1, [R0]
CMP R1, #1 ; if (OSIntNesting == 1) {
BNE OS_CPU_IRQ_ISR_1
LDR R4, OS_TCBCur ; OSTCBCur->OSTCBStkPtr = SP
LDR R5, [R4]
STR SP, [R5] ; }
OS_CPU_IRQ_ISR_1
MSR CPSR_c, #(NO_INT | IRQ32_MODE) ; Change to IRQ mode (to use the IRQ stack to handle interrupt)
LDR R0, OS_CPU_IRQ_ISR_Handler ; OS_CPU_IRQ_ISR_Handler();
MOV LR, PC
BX R0
MSR CPSR_c, #(NO_INT | SVC32_MODE) ; Change to SVC mode
LDR R0, OS_IntExit ; OSIntExit();
MOV LR, PC
BX R0 ; RESTORE NEW TASK'S CONTEXT
LDMFD SP!, {R4} ; Pop new task's CPSR
MSR SPSR_cxsf, R4
LDMFD SP!, {R0-R12,LR,PC}^ ; Pop new task's context
RSEG CODE:CODE:NOROOT(2)
CODE32
OS_CPU_FIQ_ISR
STMFD SP!, {R1-R3} ; PUSH WORKING REGISTERS ONTO FIQ STACK
MOV R1, SP ; Save FIQ stack pointer
ADD SP, SP,#12 ; Adjust FIQ stack pointer
SUB R2, LR,#4 ; Adjust PC for return address to task
MRS R3, SPSR ; Copy SPSR (i.e. interrupted task's CPSR) to R3
MSR CPSR_c, #(NO_INT | SVC32_MODE) ; Change to SVC mode
; SAVE TASK'S CONTEXT ONTO TASK'S STACK
STMFD SP!, {R2} ; Push task's Return PC
STMFD SP!, {LR} ; Push task's LR
STMFD SP!, {R4-R12} ; Push task's R12-R4
LDMFD R1!, {R4-R6} ; Move task's R1-R3 from FIQ stack to SVC stack
STMFD SP!, {R4-R6}
STMFD SP!, {R0} ; Push task's R0 onto task's stack
STMFD SP!, {R3} ; Push task's CPSR (i.e. FIQ's SPSR)
; HANDLE NESTING COUNTER
LDR R0, OS_IntNesting ; OSIntNesting++;
LDRB R1, [R0]
ADD R1, R1,#1
STRB R1, [R0]
CMP R1, #1 ; if (OSIntNesting == 1){
BNE OS_CPU_FIQ_ISR_1
LDR R4, OS_TCBCur ; OSTCBCur->OSTCBStkPtr = SP
LDR R5, [R4]
STR SP, [R5] ; }
OS_CPU_FIQ_ISR_1
MSR CPSR_c, #(NO_INT | FIQ32_MODE) ; Change to FIQ mode (to use the FIQ stack to handle interrupt)
LDR R0, ??OS_CPU_FIQ_ISR_Handler ; OS_CPU_FIQ_ISR_Handler();
MOV LR, PC
BX R0
MSR CPSR_c, #(NO_INT | SVC32_MODE) ; Change to SVC mode
LDR R0, OS_IntExit ; OSIntExit();
MOV LR, PC
BX R0 ; RESTORE NEW TASK'S CONTEXT
LDMFD SP!, {R4} ; Pop new task's CPSR
MSR SPSR_cxsf, R4
LDMFD SP!, {R0-R12,LR,PC}^ ; Pop new task's context
4) OSStartHighRdy()函数
该函数是在OSStart()多任务启动后，负责从最高优先级任务的TCB控制块中获得该任务的堆栈指针SP通过SP依次将CPU现场恢复。这时系统就将控制权交给用户创建的该任务进程，直到该任务被阻塞或者被更高优先级的任务抢占CPU。该函数仅仅在多任务启动时被执行一次，用来启动第一个也即最高优先级任务。
OSStartHighRdy
MSR CPSR_cxsf, #0xD3 ; Switch to SVC mode with IRQ and FIQ disabled
LDR R0, ??OS_TaskSwHook ; OSTaskSwHook();
MOV LR, PC
BX R0
LDR R4, OS_Running ; OSRunning = TRUE
MOV R5, #1
STRB R5, [R4]
; SWITCH TO HIGHEST PRIORITY TASK
LDR R4, OS_TCBHighRdy ; Get highest priority task TCB address
LDR R4, [R4] ; get stack pointer
LDR SP, [R4] ; switch to the new stack
LDR R4, [SP], #4 ; pop new task's CPSR
MSR SPSR_cxsf,R4
LDMFD SP!, {R0-R12,LR,PC}^ ; pop new task's context
2. 多任务应用程序的编写
1) C语言入口函数
函数Main()为C语言入口函数，所有C程序从这里开始运行，在该函数中进行如下操作：
③ 调用函数ARMTaskgetInit初始化ARM处理器
④ 调用OSInit初始化系统
⑤ 调用OSTaskCreat函数创建任务：Task1和Task2
⑥ 调用ARMTaskgetStart函数启动时钟节拍中断
⑦ 调用OSStart启动系统任务调度
#include “config.h”
OS_STK TaskStartStk[TASK_STK_SIZE];
OS_STK TaskStk[TASK_STK_SIZE];
int Main(void){
OSInit();
OSTaskCreate(Task1,(void*)0,&TaskStartStk[TASK_STK_SIZE-1],0);
OSStart();
return();
}
2) 任务处理函数
① Task1
void Task1(void *pdata){
pdata=pdata;
TargetInit();
For(;;){
OSTimeDly(OS_TICKS_PER_SEC/50);
If(GetKey()!=KEY1) {
continue;
}
OSTaskCreate(Task2,(void *)0,&TaskStk[TASK_STK_SIZE-1],10);
While(GetKey()!=0) {
OSTimeDly(OS_TICKS_PER_SEC/50);
}
}
}
② Task2
void Task2(void *pdata){
pdata=pdata;
BeeMoo();
OSTimeDly(OS_TICKS_PER_SEC/8);
BeeMoo();
OSTimeDly(OS_TICKS_PER_SEC/4);
BeeMoo();
OSTimeDly(OS_TICKS_PER_SEC/8);
OSTaskDel(OS_PRIO_SELF);
} |
