6502.org

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08837    ; EhBASIC IRQ support
08838    
08839    IRQ_CODE
08840    FF7D  48           	PHA				; save A
08841    FF7E  A5 DF        	LDA	IrqBase		; get the IRQ flag byte
08842    FF80  4A           	LSR				; shift the set b7 to b6, and on down ...
08843    FF81  05 DF        	ORA	IrqBase		; OR the original back in
08844    FF83  85 DF        	STA	IrqBase		; save the new IRQ flag byte
08845    FF85  68           	PLA				; restore A
08846    FF86  40           	RTI

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  PHA  ;save a & x
  TXA
  PHA
...
  TSX  ;point x to saved processor status
  INX
  INX
  INX
  LDA $100,x  ;set interrupt disable on stack
; could use LDA/STA $103,x instead if you assume, that one never uses the bottom of the stack
  ORA #4
  STA $100,x
...
  PLA  ;restore x & a
  TAX
  PLA

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setirq:              ; Use to record IRQ for NEXT.  Put this address in MIRQVEC. 
     STZ  irqnot     ; Record that interrupt was req'ed by storing 0 in irqnot.  
     STA  tempA      ; Temporarily save accumulator in tempA to restore below.   
        PLA          ; Pull saved processor status byte off the μP stack,        
        ORA  #4      ; set the bit corresponding to the interrupt disable,       
        PHA          ; and push the revised status byte back on the stack.       
     LDA  tempA      ; Restore the accumulator content.                          
     RTI             ; Return from interrupt.  μP status gets restored modified.

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;------------------------------------------------------------------------------
; 100 Hz interrupt
; - takes care of "flashing" the cursor
;------------------------------------------------------------------------------
;
p100Hz:
	cld			; clear extended precision mode
	pha
	phx
	phy

	; support EhBASIC's IRQ functionality
	; code derived from minimon.asm
;	lda		#3				; Timer is IRQ #3
;	sta		IrqSource		; stuff a byte indicating the IRQ source for PEEK()
;	lb		r1,IrqBase		; get the IRQ flag byte
;	lsr						; shift the set b7 to b6, and on down ...
;	orb		r1,r1,IrqBase	; OR the original back in
;	sb		r1,IrqBase		; save the new IRQ flag byte

	; support tiny basic's IRQ rout
	inc		IRQFlag			

	inc		TEXTSCR+83
	stz		0xFFDCFFFC		; clear interrupt
	
	; flash the cursor
	lda		CursorFlash
	beq		p100Hz1
	jsr		CalcScreenLoc
	tay
	lda		$10000,y
	ldx		IRQFlag
	and		r2,r2,#$0F
	and		#$F0
	or		r1,r1,r2
	sta		$10000,y
p100Hz1
	ply
	plx
	pla
	rti

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   200 = 000000DC                      NmiBase		EQU		0xDC
    201 = 000000DF                      IrqBase		EQU		0xDF
                                        
                                        
                                        
    205 = 00000500                      SP8Save		EQU		0x500		; SP8Save area $500 to $5FF
    206 = 00000600                      SPSave		EQU		0x600		; SPSave area $600 to $6FF
                                        ; TinyBasic AREA = 0x700 to 0x77F
                                        
    209 = 00000780                      HeadRdy0	EQU		0x780
    210 = 00000781                      HeadRdy1	EQU		HeadRdy0+1
    211 = 00000782                      HeadRdy2	EQU		HeadRdy1+1
    212 = 00000783                      HeadRdy3	EQU		HeadRdy2+1

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; BASIC warm start entry point
; wait for Basic command

LAB_1274
					; clear ON IRQ/NMI bytes
	LDA	#$00			; clear A
	STA	IrqBase		; clear enabled byte
	STA	NmiBase		; clear enabled byte
	CLI				; allow interrupts
	LDA	#<LAB_RMSG		; point to "Ready" message low byte
	LDY	#>LAB_RMSG		; point to "Ready" message high byte

	JSR	LAB_18C3		; go do print string

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strStartQue:
	db		1,0,0,0,2,0,0,0,3,1,0,0,4,0,0,0

;------------------------------------------------------------------------------
; 100 Hz interrupt
; - takes care of "flashing" the cursor
; - switching tasks
;------------------------------------------------------------------------------
;
p100Hz:
	; Handle every other interrupt because 100Hz interrupts may be too fast.
	pha
	lda		IRQFlag
	ina
	sta		IRQFlag
	ror
	bcc		p100Hz11	
	pla
	rti

p100Hz11:

	cld		; clear extended precision mode

	; save off regs on the stack
	phx
	phy
	push	r4
	push	r5
	push	r6
	push	r7
	push	r8
	push	r9
	push	r10
	push	r11
	push	r12
	push	r13
	push	r14
	push	r15
	ldx		TaskNo
	and		r2,r2,#$FF
	tsa						; save off the stack pointer
	sta		TCB_SPSave,x
	tsr		sp8,r1			; and the eight bit mode stack pointer
	sta		TCB_SP8Save,x

	; support EhBASIC's IRQ functionality
	; code derived from minimon.asm
	lda		#3				; Timer is IRQ #3
	sta		IrqSource		; stuff a byte indicating the IRQ source for PEEK()
	lb		r1,IrqBase		; get the IRQ flag byte
	ora		#$20			; set IRQ pending bit
	sb		r1,IrqBase


	inc		TEXTSCR+83		; update IRQ live indicator on screen
	stz		0xFFDCFFFC		; clear interrupt
	
	; flash the cursor
	lda		CursorFlash		; test if we want a flashing cursor
	beq		p100Hz1a
	jsr		CalcScreenLoc	; compute cursor location in memory
	tay
	lda		$10000,y		; get color code $10000 higher in memory
	ldx		IRQFlag			; get counter
	and		r2,r2,#$0F		; limit to low order nybble
	and		#$F0			; prepare to or in new value, mask off foreground color
	or		r1,r1,r2		; set new foreground color for cursor
	sta		$10000,y		; store the color code back to memory
p100Hz1a

	; Check the timeout list to see if there are items ready to be removed from
	; the list. Also decrement the timeout of the item at the head of the list.

p100Hz15:	
	ldx		TimeoutList
	bmi		p100Hz12				; are there any entries in the timeout list ?
	lda		TCB_Timeout,x
	bne		p100Hz14				; has this entry timed out ?
	txa
	jsr		RemoveFromTimeoutList
	jsr		AddTaskToReadyList
	bra		p100Hz15				; go back and see if there's another task to be removed

p100Hz14:
	dea								; decrement the entries timeout
	sta		TCB_Timeout,x
	
p100Hz12:
	; Search the ready queues for a ready task.
	; The search is occasionally started at a lower priority queue in order
	; to prevent starvation of lower priority tasks. This is managed by 
	; using a tick count as an index to a string containing the start que.

	ld		r6,#5			; number of queues to search
	ldy		IRQFlag			; use the IRQFlag as a buffer index
	lsr		r3,r3,#1		; the LSB is always the same
	and		r3,r3,#$0F		; counts from 0 to 15
	lb		r3,strStartQue,y	; get the queue to start search at
p100Hz2:
	lda		HeadRdy0,y
	bmi		p100Hz1
	; Move the head of the ready queue to the tail
	ldx		TailRdy0,y
	sta		TCB_NxtRdy,x
	sta		TailRdy0,y
	lda		HeadRdy0,y
	tax
	lda		TCB_NxtRdy,x
	php
	ld	    r4,#-1	
	st		r4,TCB_NxtRdy,x
	plp
	bpl		p100Hz4
	; here there is no next ready task
	; so we just stay with the same task
	lda		HeadRdy0,y
p100Hz4:
	sta		HeadRdy0,y
	sta		TaskNo
	bra		p100Hz3
p100Hz1:
	iny
	cpy		#5
	bne		p100Hz5
	ldy		#0
p100Hz5
	dec		r6
	bne		p100Hz2

	; here there were no tasks ready
	stz		TaskNo			; select BIOS task
p100Hz3:
p100Hz10
	ldx		TaskNo
	and		r2,r2,#$FF
	lda		TCB_SP8Save,x		; get back eight bit stack pointer
	trs		r1,sp8
	ldx		TCB_SPSave,x		; get back stack pointer
	txs
	; restore registers
	pop		r15
	pop		r14
	pop		r13
	pop		r12
	pop		r11
	pop		r10
	pop		r9
	pop		r8
	pop		r7
	pop		r6
	pop		r5
	pop		r4
	ply
	plx
	pla
	rti


;------------------------------------------------------------------------------
; 1000 Hz interrupt
; This IRQ must be fast.
; Increments the millisecond counter
;------------------------------------------------------------------------------
;
p1000Hz:
	stz		0xFFDCFFFD				; acknowledge interrupt
	inc		Milliseconds			; increment milliseconds count
	rti

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   ; support EhBASIC's IRQ functionality
   ; code derived from minimon.asm
   lda      #3            ; Timer is IRQ #3
   sta      IrqSource      ; stuff a byte indicating the IRQ source for PEEK()
   lb      r1,IrqBase      ; get the IRQ flag byte
   ora      #$20         ; set IRQ pending bit
   sb      r1,IrqBase