📄 os_cpu_a.s
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;********************************************************************************************************
; uC/OS-II
; The Real-Time Kernel
;
; (c) Copyright 2002, Jean J. Labrosse, Weston, FL
; All Rights Reserved
;
;
; PAGED S12 Specific code
; (METROWERKS)
;
; File : OS_CPU_A.S
; By : Eric Shufro
;
; Notes : THIS FILE *MUST* BE LINKED INTO NON_BANKED MEMORY!
;********************************************************************************************************
NON_BANKED: section
;********************************************************************************************************
; I/O PORT ADDRESSES
;********************************************************************************************************
PPAGE: equ $0030 ; Addres of PPAGE register (assuming MC9S12 (non XGATE part)
;********************************************************************************************************
; PUBLIC DECLARATIONS
;********************************************************************************************************
xdef OS_CPU_SR_Save
xdef OS_CPU_SR_Restore
xdef OSStartHighRdy
xdef OSCtxSw
xdef OSIntCtxSw
xdef OSTickISR
;********************************************************************************************************
; EXTERNAL DECLARATIONS
;********************************************************************************************************
xref OSIntExit
xref OSIntNesting
xref OSPrioCur
xref OSPrioHighRdy
xref OSRunning
xref OSTaskSwHook
xref OSTCBCur
xref OSTCBHighRdy
xref OSTickISR_Handler
xref OSTimeTick
;********************************************************************************************************
; SAVE THE CCR AND DISABLE INTERRUPTS
; &
; RESTORE CCR
;
; Description : These function implements OS_CRITICAL_METHOD #3
;
; Arguments : The function prototypes for the two functions are:
; 1) OS_CPU_SR OSCPUSaveSR(void)
; where OS_CPU_SR is the contents of the CCR register prior to disabling
; interrupts.
; 2) void OSCPURestoreSR(OS_CPU_SR os_cpu_sr);
; 'os_cpu_sr' the the value of the CCR to restore.
;
; Note(s) : 1) It's assumed that the compiler uses the D register to pass a single 16-bit argument
; to and from an assembly language function.
;********************************************************************************************************
OS_CPU_SR_Save:
tfr ccr,b ; It's assumed that 8-bit return value is in register B
sei ; Disable interrupts
rtc ; Return to caller with D containing the previous CCR
OS_CPU_SR_Restore:
tfr b,ccr ; B contains the CCR value to restore, move to CCR
rtc
;********************************************************************************************************
; START HIGHEST PRIORITY TASK READY-TO-RUN
;
; Description : This function is called by OSStart() to start the highest priority task that was created
; by your application before calling OSStart().
;
; Arguments : none
;
; Note(s) : 1) The stack frame is assumed to look as follows:
;
; OSTCBHighRdy->OSTCBStkPtr + 0 PPAGE
; + 1 CCR
; + 2 B
; + 3 A
; + 4 X (H)
; + 5 X (L)
; + 6 Y (H)
; + 7 Y (L)
; + 8 PC(H)
; + 9 PC(L)
;
; 2) OSStartHighRdy() MUST:
; a) Call OSTaskSwHook() then,
; b) Set OSRunning to TRUE,
; c) Switch to the highest priority task by loading the stack pointer of the
; highest priority task into the SP register and execute an RTI instruction.
;********************************************************************************************************
OSStartHighRdy:
call OSTaskSwHook ; 4~, Invoke user defined context switch hook
ldab #$01 ; 2~, Indicate that we are multitasking
stab OSRunning ; 4~
ldx OSTCBHighRdy ; 3~, Point to TCB of highest priority task ready to run
lds 0,x ; 3~, Load SP into 68HC12
pula ; 3~, Get value of PPAGE register
staa PPAGE ; 3~, Store into CPU's PPAGE register
rti ; 4~, Run task
;********************************************************************************************************
; TASK LEVEL CONTEXT SWITCH
;
; Description : This function is called when a task makes a higher priority task ready-to-run.
;
; Arguments : none
;
; 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 + 0 PC(H)
; + 1 PC(L)
;
; 3) The stack frame of the task to resume looks as follows:
;
; OSTCBHighRdy->OSTCBStkPtr + 0 PPAGE
; + 1 CCR
; + 2 B
; + 3 A
; + 4 X (H)
; + 5 X (L)
; + 6 Y (H)
; + 7 Y (L)
; + 8 PC(H)
; + 9 PC(L)
;********************************************************************************************************
OSCtxSw:
ldaa PPAGE ; 3~, Get current value of PPAGE register
psha ; 2~, Push PPAGE register onto current task's stack
ldy OSTCBCur ; 3~, OSTCBCur->OSTCBStkPtr = Stack Pointer
sts 0,y ; 3~,
call OSTaskSwHook ; 4~, Call user task switch hook
ldx OSTCBHighRdy ; 3~, OSTCBCur = OSTCBHighRdy
stx OSTCBCur ; 3~
ldab OSPrioHighRdy ; 3~, OSPrioCur = OSPrioHighRdy
stab OSPrioCur ; 3~
lds 0,x ; 3~, Load SP into 68HC12
pula ; 3~, Get value of PPAGE register
staa PPAGE ; 3~, Store into CPU's PPAGE register
rti ; 8~, Run task
;********************************************************************************************************
; INTERRUPT LEVEL CONTEXT SWITCH
;
; Description : This function is called by OSIntExit() to perform a context switch to a task that has
; been made ready-to-run by an ISR. The PPAGE register of the preempted task has already
; been stacked during the start of the ISR that is currently running.
;
; Arguments : none
;********************************************************************************************************
OSIntCtxSw:
call OSTaskSwHook ; 4~, Call user task switch hook
ldx OSTCBHighRdy ; 3~, OSTCBCur = OSTCBHighRdy
stx OSTCBCur ; 3~
ldab OSPrioHighRdy ; 3~, OSPrioCur = OSPrioHighRdy
stab OSPrioCur ; 3~
lds 0,x ; 3~, Load the SP of the next task
pula ; 3~, Get value of PPAGE register
staa PPAGE ; 3~, Store into CPU's PPAGE register
rti ; 8~, Run task
;********************************************************************************************************
; SYSTEM TICK ISR
;
; Description : This function is the ISR used to notify uC/OS-II that a system tick has occurred. You
; must setup the S12XE's interrupt vector table so that an OUTPUT COMPARE interrupt
; vectors to this function.
;
; Arguments : none
;
; Notes : 1) The 'tick ISR' assumes the we are using the Output Compare specified by OS_TICK_OC
; (see APP_CFG.H and this file) to generate a tick that occurs every OS_TICK_OC_CNTS
; (see APP_CFG.H) which corresponds to the number of FRT (Free Running Timer)
; counts to the next interrupt.
;
; 2) All USER interrupts should be modeled EXACTLY like this where the only
; line to be modified is the call to your ISR_Handler and perhaps the call to
; the label name OSTickISR1.
;********************************************************************************************************
OSTickISR:
ldaa PPAGE ; 3~, Get current value of PPAGE register
psha ; 2~, Push PPAGE register onto current task's stack
inc OSIntNesting ; 4~, Notify uC/OS-II about ISR
ldab OSIntNesting ; 4~, if (OSIntNesting == 1) {
cmpb #$01 ; 2~
bne OSTickISR1 ; 3~
ldy OSTCBCur ; 3~, OSTCBCur->OSTCBStkPtr = Stack Pointer
sts 0,y ; 3~, }
OSTickISR1:
call OSTickISR_Handler
; cli ; 2~, Enable interrupts to allow interrupt nesting
call OSIntExit ; 6~+, Notify uC/OS-II about end of ISR
pula ; 3~, Get value of PPAGE register
staa PPAGE ; 3~, Store into CPU's PPAGE register
rti ; 12~, Return from interrupt, no higher priority tasks ready.
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