?? os_cpu_a.asm
字號(hào):
; BX
; DX
; CX
; AX
; OFFSET of task code address
; SEGMENT of task code address
; Flags to load in PSW (High memory)
;*********************************************************************************************************
_OSIntCtxSw PROC FAR
;
CALL FAR PTR _OSTaskSwHook ; Call user defined task switch hook
;調(diào)用用戶定義的task switch hook
MOV AX, SEG _OSTCBCur ; Reload DS in case it was altered
MOV DS, AX ;
;如果DS改變的話，就重裝DS
MOV AX, WORD PTR DS:_OSTCBHighRdy+2 ; OSTCBCur = OSTCBHighRdy
MOV DX, WORD PTR DS:_OSTCBHighRdy ;
MOV WORD PTR DS:_OSTCBCur+2, AX ;
MOV WORD PTR DS:_OSTCBCur, DX ; 同上
;
MOV AL, BYTE PTR DS:_OSPrioHighRdy ; OSPrioCur = OSPrioHighRdy
MOV BYTE PTR DS:_OSPrioCur, AL
;
LES BX, DWORD PTR DS:_OSTCBHighRdy ; SS:SP = OSTCBHighRdy->OSTCBStkPtr
MOV SS, ES:[BX+2] ;
MOV SP, ES:[BX] ;
;
POP DS ; Load new task's context
POP ES ; 中斷已經(jīng)將CPU寄存器保存進(jìn)棧
POPA ;
;
IRET ; Return to new task
;
_OSIntCtxSw ENDP
PAGE ; /*$PAGE*/
;*********************************************************************************************************
; RESTORE FPU REGISTERS
; void OSFPRestore(void *pblk)
;
; Description : This function is called to restore the contents of the FPU registers during a context
; switch. It is assumed that a pointer to a storage area for the FPU registers is placed
; in the task's TCB (i.e. .OSTCBExtPtr).
; Arguments : pblk is passed to this function when called.
; Note(s) : 1) The stack frame upon entry looks as follows:
;
; SP + 0 -> OFFSET of caller (Low memory)
; + 2 SEGMENT of caller
; + 4 OFFSET of pblk
; + 6 SEGMENT of pblk (High memory)
; 取FPU寄存器
;*********************************************************************************************************
_OSFPRestore PROC FAR
; SP和BP為指針寄存器，把整型寄存器的值保存到當(dāng)前的任務(wù)堆棧中。
PUSH BP ; Save work registers
MOV BP,SP
PUSH ES
PUSH BX
;放在ES：BX中的指針作為自變量傳給OSFPRestore().
LES BX, DWORD PTR [BP+6] ; Point to 'pblk'
;LES是地址傳送指令，將源地址傳送到ES寄存器
FRSTOR ES:[BX] ; Restore FPU context
;執(zhí)行浮點(diǎn)單元指令。
POP BX ; Restore work registers
POP ES;恢復(fù)臨時(shí)寄存器
POP BP
;
RET ; Return to caller
;
_OSFPRestore ENDP
PAGE ; /*$PAGE*/
;*********************************************************************************************************
; SAVE FPU REGISTERS
; void OSFPSave(void *pblk)
;
; Description : This function is called to save the contents of the FPU registers during a context
; switch. It is assumed that a pointer to a storage area for the FPU registers is placed
; in the task's TCB (i.e. .OSTCBExtPtr).
; Arguments : pblk is passed to this function when called.
; Note(s) : 1) The stack frame upon entry looks as follows:
;
; SP + 0 -> OFFSET of caller (Low memory)
; + 2 SEGMENT of caller
; + 4 OFFSET of pblk
; + 6 SEGMENT of pblk (High memory)
; 保存FPU寄存器
;*********************************************************************************************************
_OSFPSave PROC FAR
;
PUSH BP ; Save work registers
MOV BP,SP
PUSH ES
PUSH BX
;
LES BX, DWORD PTR [BP+6] ; Point to 'pblk'
;LES是地址傳送指令，將源地址傳送到ES寄存器
FSAVE ES:[BX] ; Save FPU context
;
POP BX ; Restore work registers
POP ES
POP BP
;
RET ; Return to caller
;
_OSFPSave ENDP
PAGE ; /*$PAGE*/
;*********************************************************************************************************
; HANDLE TICK ISR
;
; Description: This function is called 199.99 times per second or, 11 times faster than the normal DOS
; tick rate of 18.20648 Hz. Thus every 11th time, the normal DOS tick handler is called.
; This is called chaining. 10 times out of 11, however, the interrupt controller on the PC
; must be cleared to allow for the next interrupt.
;
; Arguments : none
;
; Returns : none
;
; Note(s) : The following C-like pseudo-code describe the operation being performed in the code below.
;
; Save all registers on the current task's stack;
; OSIntNesting++;
; if (OSIntNesting == 1) {
; OSTCBCur->OSTCBStkPtr = SS:SP
; }
; OSTickDOSCtr--;
; if (OSTickDOSCtr == 0) {
; OSTickDOSCtr = 11;
; INT 81H; Chain into DOS every 54.925 mS
; (Interrupt will be cleared by DOS)
; } else {
; Send EOI to PIC; Clear tick interrupt by sending an End-Of-Interrupt to the 8259
; PIC (Priority Interrupt Controller)
; }
; OSTimeTick(); Notify uC/OS-II that a tick has occured
; OSIntExit(); Notify uC/OS-II about end of ISR
; Restore all registers that were save on the current task's stack;
; Return from Interrupt;
;*********************************************************************************************************
;
_OSTickISR PROC FAR
;
PUSHA ; Save interrupted task's context
PUSH ES ;保存CPU寄存器內(nèi)容
PUSH DS
;
MOV AX, SEG(_OSIntNesting) ; Reload DS
MOV DS, AX
INC BYTE PTR DS:_OSIntNesting ; Notify uC/OS-II of ISR
;中斷嵌套加一
CMP BYTE PTR DS:_OSIntNesting, 1 ; if (OSIntNesting == 1)
JNE SHORT _OSTickISR1 ;如果不等于一，跳到 _OSTickISR1
MOV AX, SEG(_OSTCBCur) ; Reload DS
MOV DS, AX
LES BX, DWORD PTR DS:_OSTCBCur ; OSTCBCur->OSTCBStkPtr = SS:SP
MOV ES:[BX+2], SS ;
MOV ES:[BX+0], SP ;
;
_OSTickISR1:
MOV AX, SEG(_OSTickDOSCtr) ; Reload DS
MOV DS, AX
DEC BYTE PTR DS:_OSTickDOSCtr
CMP BYTE PTR DS:_OSTickDOSCtr, 0
JNE SHORT _OSTickISR2 ; Every 11 ticks (~199.99 Hz), chain into DOS
;11個(gè)時(shí)鐘節(jié)拍，跳進(jìn)DOS
MOV BYTE PTR DS:_OSTickDOSCtr, 11
INT 081H ; Chain into DOS's tick ISR
;跳到DOS的節(jié)拍中斷
JMP SHORT _OSTickISR3
_OSTickISR2:
MOV AL, 20H ; Move EOI code into AL.
MOV DX, 20H ; Address of 8259 PIC in DX.
OUT DX, AL ; Send EOI to PIC if not processing DOS timer.
;
_OSTickISR3:
CALL FAR PTR _OSTimeTick ; Process system tick調(diào)用時(shí)鐘節(jié)拍處理函數(shù)
;
CALL FAR PTR _OSIntExit ; Notify uC/OS-II of end of ISR
;通知退出中斷處理程序
POP DS ; Restore interrupted task's context
POP ES
POPA
;
IRET ; Return to interrupted task
;
_OSTickISR ENDP
;
END
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