;********************************************************************************************************
;                                               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
;
;                                           Borland C/C++ V4.51
;                                       (IBM/PC Compatible Target)
;
; File         : OS_CPU_A.ASM
; By           : Jean J. Labrosse
;********************************************************************************************************

			AREA |.text|, CODE, READONLY

;********************************************************************************************************
;                                    PUBLIC and EXTERNAL REFERENCES
;********************************************************************************************************

			EXPORT OSTickISR
			EXPORT OSStartHighRdy
			EXPORT OSCtxSw
			EXPORT OSIntCtxSw

			IMPORT OSIntEnter
			IMPORT OSIntExit
			IMPORT OSTimeTick
			IMPORT OSTaskSwHook

			IMPORT OSIntNesting
			IMPORT OSPrioHighRdy
			IMPORT OSPrioCur
			IMPORT OSRunning
			IMPORT OSTCBCur
			IMPORT OSTCBHighRdy


;*********************************************************************************************************
;                                          START MULTITASKING
;                                       void OSStartHighRdy(void)
;
; Note : OSStartHighRdy() MUST:
;           a) Call OSTaskSwHook() then,
;           b) Set OSRunning to TRUE,
;           c) Switch to the highest priority task.
;*********************************************************************************************************

OSStartHighRdy	FUNCTION

			MSR		CPSR_c, #0xd3					; Switch to SVC mode with IRQ and FIQ disabled
			BL		OSTaskSwHook					; Call user defined task switch hook

			LDR		r0, =OSRunning					; OSRunning = TRUE;
			MOV		r1, #1							;   (Indicates that multitasking has started)
			STRB	r1, [r0]

			LDR		r0, =OSTCBHighRdy				; sp = OSTCBHighRdy->OSTCBStkPtr
			LDR		r1, [r0]
			LDR		sp, [r1]

			LDR		r0, [sp], #4					; Load task's context
			MSR		SPSR_cxsf, r0
			LDMFD	sp!, {r0 - r12, lr, pc}^		; Run task

			ENDFUNC

;*********************************************************************************************************
;                                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
;
;*********************************************************************************************************

OSCtxSw		FUNCTION

			STR		lr, [sp, #-4]!					; Save current task's context
			STMFD	sp!, {r0 - r12, lr}
			MRS		r0, CPSR
			STR		r0, [sp, #-4]!

			LDR		r0, =OSTCBCur					; OSTCBCur->OSTCBStkPtr = sp
			LDR		r1, [r0]
			STR		sp, [r1]

			BL		OSTaskSwHook					; Call user defined task switch hook

			LDR		r0, =OSPrioHighRdy				; OSPrioCur = OSPrioHighRdy
			LDR		r1, =OSPrioCur
			LDRB	r2, [r0]
			STRB	r2, [r1]

			LDR		r0, =OSTCBHighRdy				; OSTCBCur = OSTCBHighRdy
			LDR		r1, =OSTCBCur
			LDR		r2, [r0]
			STR		r2, [r1]

			LDR		sp, [r2]						; sp = OSTCBHighRdy->OSTCBStkPtr

			LDR		r0, [sp], #4					; Load task's context
			MSR		SPSR_cxsf, r0
			LDMFD	sp!, {r0 - r12, lr, pc}^		; Run task

			ENDFUNC

;*********************************************************************************************************
;                                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
;
;*********************************************************************************************************

OSIntCtxSw	FUNCTION

			BL		OSTaskSwHook					; Call user defined task switch hook

			LDR		r0, =OSPrioHighRdy				; OSPrioCur = OSPrioHighRdy
			LDR		r1, =OSPrioCur
			LDRB	r2, [r0]
			STRB	r2, [r1]

			LDR		r0, =OSTCBHighRdy				; OSTCBCur = OSTCBHighRdy
			LDR		r1, =OSTCBCur
			LDR		r2, [r0]
			STR		r2, [r1]

			LDR		sp, [r2]						; sp = OSTCBHighRdy->OSTCBStkPtr

			LDR		r0, [sp], #4					; Load task's context
			MSR		SPSR_cxsf, r0
			LDMFD	sp!, {r0 - r12, lr, pc}^		; Run task

			ENDFUNC

;*********************************************************************************************************
;                                            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
;
;*********************************************************************************************************

OSTickISR	FUNCTION

			STMFD	sp!, {r0 - r2}					; Save working registers onto IRQ stack
			SUB		r2, lr, #4
			MOV		r0, sp
			MRS		r1, SPSR
			ADD		sp, sp, #12

			MSR		CPSR_c, #0xd3					; Switch to SVC mode

			STR		r2, [sp, #-4]!					; Save task's context onto task's stack
			STMFD	sp!, {r3 - r12, lr}
			LDMFD	r0!, {r3 - r5}					; Move task's r0-r2 from IRQ stack to task's stack
			STMFD	sp!, {r3 - r5}
			STR		r1, [sp, #-4]!					; Save task's CPSR

			BL		OSIntEnter						; Notify uC/OS-II of ISR

			LDR		r0, =OSIntNesting				; if (OSIntNesting == 1)
			LDRB	r1,[r0]
			CMP		r1, #1
			BNE		%F0
			LDR		r0, =OSTCBCur					;   OSTCBCur->OSTCBStkPtr = sp
			LDR		r1, [r0]
			STR		sp, [r1]
0
			LDR		r0, =0x0a80000c					; Clear interrupt source
			MOV		r1, #0
			STR		r1, [r0]

			BL		OSTimeTick						; Process system tick

			BL		OSIntExit						; Notify uC/OS-II of end of ISR

			LDR		r0, [sp], #4					; Load task's context
			MSR		SPSR_cxsf, r0
			LDMFD	sp!, {r0 - r12, lr, pc}^		; Run task

			ENDFUNC


            END