📄 os_cpu_a.asm
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;********************************************************************************************************
; uC/OS-II
; The Real-Time Kernel
;
; (c) Copyright 1992-2002, Jean J. Labrosse, Weston, FL
; All Rights Reserved
;
;
; 80x86/80x88 Specific code
; LARGE MEMORY MODEL
;
; Pacific Hi-Tech C Compiler
; (IBM/PC Compatible Target)
;
; File : OS_CPU_A.ASM
; By : Jean J. Labrosse
; Modified by : Tony Richardson
;********************************************************************************************************
;********************************************************************************************************
; PUBLIC and EXTERNAL REFERENCES
;********************************************************************************************************
.GLOBL _OSTickISR ; Public
.GLOBL _OSStartHighRdy ; Public
.GLOBL _OSCtxSw ; Public
.GLOBL _OSIntCtxSw ; Public
.GLOBL _OSIntExit ; External, Far
.GLOBL _OSTimeTick ; External, Far
.GLOBL _OSTaskSwHook ; External, Far
.GLOBL _OSIntNesting ; External, Byte
.GLOBL _OSTickDOSCtr ; External, Byte
.GLOBL _OSPrioHighRdy ; External, Byte
.GLOBL _OSPrioCur ; External, Byte
.GLOBL _OSRunning ; External, Byte
.GLOBL _OSTCBCur ; External, Dword
.GLOBL _OSTCBHighRdy ; External, Dword
.186
.PSECT _TEXT
;*********************************************************************************************************
; START MULTITASKING
; void OSStartHighRdy(void)
;
; The stack frame is assumed to look as follows:
;
; OSTCBHighRdy->OSTCBStkPtr --> DS (Low memory)
; ES
; DI
; SI
; BP
; SP
; BX
; DX
; CX
; AX
; OFFSET of task code address
; SEGMENT of task code address
; Flags to load in PSW
; OFFSET of task code address
; SEGMENT of task code address
; OFFSET of 'pdata'
; SEGMENT of 'pdata' (High memory)
;
; Note : OSStartHighRdy() MUST:
; a) Call OSTaskSwHook() then,
; b) Set OSRunning to TRUE,
; c) Switch to the highest priority task.
;*********************************************************************************************************
_OSStartHighRdy:
MOV AX, #SEG _OSTCBHighRdy ; Reload DS
MOV DS, AX ;
;
CALLF _OSTaskSwHook ; Call user defined task switch hook
;
MOV AL, #1 ; OSRunning = TRUE;
MOV DS:_OSRunning, AL ; (Indicates that multitasking has started)
;
LES BX, DS:_OSTCBHighRdy ; SS:SP = OSTCBHighRdy->OSTCBStkPtr
MOV SS, ES:2[BX] ;
MOV SP, ES:[BX] ;
;
POP DS ; Load task's context
POP ES ;
POPA ;
;
IRET ; Run task
;*********************************************************************************************************
; PERFORM A CONTEXT SWITCH (From task level)
; void OSCtxSw(void)
;
; Note(s): 1) Upon entry,
; OSTCBCur points to the OS_TCB of the task to suspend
; OSTCBHighRdy points to the OS_TCB of the task to resume
;
; 2) The stack frame of the task to suspend looks as follows:
;
; SP -> OFFSET of task to suspend (Low memory)
; SEGMENT of task to suspend
; PSW of task to suspend (High memory)
;
; 3) The stack frame of the task to resume looks as follows:
;
; OSTCBHighRdy->OSTCBStkPtr --> DS (Low memory)
; ES
; DI
; SI
; BP
; SP
; BX
; DX
; CX
; AX
; OFFSET of task code address
; SEGMENT of task code address
; Flags to load in PSW (High memory)
;*********************************************************************************************************
_OSCtxSw:
;
PUSHA ; Save current task's context
PUSH ES ;
PUSH DS ;
;
MOV AX, #SEG _OSTCBCur ; Reload DS in case it was altered
MOV DS, AX ;
;
LES BX, DS:_OSTCBCur ; OSTCBCur->OSTCBStkPtr = SS:SP
MOV ES:2[BX], SS ;
MOV ES:[BX], SP ;
;
CALLF _OSTaskSwHook ; Call user defined task switch hook
;
MOV AX, DS:_OSTCBHighRdy+2 ; OSTCBCur = OSTCBHighRdy
MOV DX, DS:_OSTCBHighRdy ;
MOV DS:_OSTCBCur+2, AX ;
MOV DS:_OSTCBCur, DX ;
;
MOV AL, DS:_OSPrioHighRdy ; OSPrioCur = OSPrioHighRdy
MOV DS:_OSPrioCur, AL ;
;
LES BX, DS:_OSTCBHighRdy ; SS:SP = OSTCBHighRdy->OSTCBStkPtr
MOV SS, ES:2[BX] ;
MOV SP, ES:[BX] ;
;
POP DS ; Load new task's context
POP ES ;
POPA ;
;
IRET ; Return to new task
;
;*********************************************************************************************************
; PERFORM A CONTEXT SWITCH (From an ISR)
; void OSIntCtxSw(void)
;
; Note(s): 1) Upon entry,
; OSTCBCur points to the OS_TCB of the task to suspend
; OSTCBHighRdy points to the OS_TCB of the task to resume
;
; 2) The stack frame of the task to suspend looks as follows:
;
; OSTCBCur->OSTCBStkPtr ------> DS (Low memory)
; ES
; DI
; SI
; BP
; SP
; BX
; DX
; CX
; AX
; OFFSET of task code address
; SEGMENT of task code address
; Flags to load in PSW (High memory)
;
;
; 3) The stack frame of the task to resume looks as follows:
;
; OSTCBHighRdy->OSTCBStkPtr --> DS (Low memory)
; ES
; DI
; SI
; BP
; SP
; BX
; DX
; CX
; AX
; OFFSET of task code address
; SEGMENT of task code address
; Flags to load in PSW (High memory)
;*********************************************************************************************************
_OSIntCtxSw:
;
CALLF _OSTaskSwHook ; Call user defined task switch hook
;
MOV AX, #SEG _OSTCBCur ; Reload DS in case it was altered
MOV DS, AX ;
;
MOV AX, DS:_OSTCBHighRdy+2 ; OSTCBCur = OSTCBHighRdy
MOV DX, DS:_OSTCBHighRdy ;
MOV DS:_OSTCBCur+2, AX ;
MOV DS:_OSTCBCur, DX ;
;
MOV AL, DS:_OSPrioHighRdy ; OSPrioCur = OSPrioHighRdy
MOV DS:_OSPrioCur, AL
;
LES BX, DS:_OSTCBHighRdy ; SS:SP = OSTCBHighRdy->OSTCBStkPtr
MOV SS, ES:2[BX] ;
MOV SP, ES:[BX] ;
;
POP DS ; Load new task's context
POP ES ;
POPA ;
;
IRET ; Return to new task
;
;*********************************************************************************************************
; 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:
;
PUSHA ; Save interrupted task's context
PUSH ES
PUSH DS
;
MOV AX, #SEG _OSIntNesting ; Reload DS
MOV DS, AX
INC DS:_OSIntNesting, BYTE ; Notify uC/OS-II of ISR
;
CMP DS:_OSIntNesting, #1, BYTE ; if (OSIntNesting == 1)
JNE _OSTickISR1
MOV AX, #SEG _OSTCBCur ; Reload DS
MOV DS, AX
LES BX, DS:_OSTCBCur ; OSTCBCur->OSTCBStkPtr = SS:SP
MOV ES:2[BX], SS ;
MOV ES:[BX], SP ;
;
_OSTickISR1:
MOV AX, #SEG _OSTickDOSCtr ; Reload DS
MOV DS, AX
DEC DS:_OSTickDOSCtr, BYTE
CMP DS:_OSTickDOSCtr, #0, BYTE
JNE _OSTickISR2 ; Every 11 ticks (~199.99 Hz), chain into DOS
;
MOV DS:_OSTickDOSCtr, #11, BYTE
INT #081H ; Chain into DOS's tick ISR
JMP _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:
CALLF _OSTimeTick ; Process system tick
;
CALLF _OSIntExit ; Notify uC/OS-II of end of ISR
;
POP DS ; Restore interrupted task's context
POP ES
POPA
;
IRET ; Return to interrupted task
;
;
.END
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