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Signetics 2650 & 2636 programming/Tutorial code - Interrupts

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Tutorial code - Interrupts

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This is the code for the tutorial Interrupts

; Tutorial - Interrupts
;=============================================================================
Reg0      equ   $1F0E           ;save r0 here during interrupts
StatusL   equ   $1F0F           ;save the program status word lower here during interrupts
Obj1dup   equ   $1F1E           ;tracks which duplicates have been output

        org     0
reset_vector:                   ; the microprocessor starts here when the reset button is pressed
        bcta,un reset
        
        org     3
interrupt_vector:
                             ;Save state of processor when interrupt occured:
        stra,r0 Reg0         ;preserve r0
        ppsl    $10          ;bank 1,  logical compare    
        spsl                             
        stra,r0 StatusL      ;save PSL with bank 1 already selected!
                             
        loda,r0 collisions   
        tmi,r0  vrle         ;case 
        bcfr,eq IVdup1       ;    interrupt caused by VRLE
        bsta,un Object1A     ;        set initial state of object 1     
        bcta,un IVend        ;        quit interrupt routine 

IVdup1:                      ;
        loda,r0 Obj1dup      ;
        comi,r0 1            ;    next duplicate is the first
        bcfr,eq IVdup2
        bsta,un Object1B     ;        set first duplicate of object 1
        bcta,un IVend        ;        quit interrupt routine 

IVdup2:                      ;
        loda,r0 Obj1dup      ;
        comi,r0 2            ;    next duplicate is the second
        bcfr,eq IVend
        bsta,un Object1C     ;        set second duplicate of object 1

IVend:                       ;Restore processor to state it was in before interrupt:
        loda,r0 StatusL                
        strz    r4           ;put a copy of PSL in r4                                
        lpsl                 ;restores psl (but with bank 1 still selected)   
        loda,r0 Reg0         ;restore r0 (but probably changes the condition code)                   
        andi,r4 $C0          ;this restores the condition code!                     
        cpsl    $10          ;switch to bank 0       
        rete,un              ;exit interrupt routine 
        
        
;======================================================================================        
reset:  
        lodi,r0 intinhibit      ; initialise program status word
        lpsu                    ;   inhibit interrupts, stack pointer=0
        lpsl                    ;   register bank 0, without carry, arithmetic compare
        eorz    r0
        stra,r0 effects         ; initialise the 74LS378
        bsta,un DefineUnused    ; push all unused objects offscreen
        lodi,r0 $AA             ; blank the score digits
        stra,r0 score12
        stra,r0 score34
        lodi,r0 %00000000       ;  X / 000              /   0     / 000
        stra,r0 backgnd         ;    / black background / disabled / black screen
        spsl    compare         ; logical compares
        cpsu    intinhibit      ; enable interrupts
endless:
        nop                     ; this is the main program loop
        nop                     ; the processor is free to perform other tasks
        nop                     ; in between servicing PVI interrupts
        bctr,un endless

;==================================================================
; subroutine  -  Primary object 
; set initial state of object 1: shape, colour, size, HC,VC
; and HCB,VCB for first duplicate, B

Object1A:
        lodi,r3 10
        lodi,r0 $FF
loop1A:
        stra,r0 shape1,r3-      ; rectangle shape
        brnr,r3 loop1A

        stra,r3 objectsize      ;  size 0

        lodi,r0 $07             ;  white
        stra,r0 colours12

        lodi,r0 10
        stra,r0 vc1             ; vc = 10
        rrl,r0
        stra,r0 vcb1            ; vcb = 20
        rrl,r0  
        stra,r0 hc1             ; hc = 40
        rrl,r0
        stra,r0 hcb1            ; vcb = 80
        lodi,r0 1
        stra,r0 Obj1dup         ;next to draw is the first duplicate
     
        retc,un
;==================================================================
; subroutine  -  First duplicate 
; set: shape, colour, size
; and VCB for second duplicate

Object1B:
        lodi,r3 10
        lodi,r0 $FF
        ppsl    withcarry       ; include carry in rotate instructions
loop1B:
        stra,r0 shape1,r3-      ; triangle shape
        cpsl    carrybit
        rrr,r0                  ; shift right with 0 from the carry bit
        brnr,r3 loop1B

        lodi,r3 1
        stra,r3 objectsize      ;  size 1

        lodi,r0 $08             ;  yellow
        stra,r0 colours12

        lodi,r0 80
        stra,r0 vcb1            ; vcb = 80
        lodi,r0 2
        stra,r0 Obj1dup         ;next to draw is the second duplicate
     
        retc,un
;==================================================================
; subroutine  -  Second duplicate 
; set: shape, colour, size, HCB
; and VCB to push next duplicate off screen

Object1C:
        lodi,r3 10
        lodi,r0 $FF
        ppsl    withcarry       ; include carry in rotate instructions
loop1C:
        stra,r0 shape1,r3-      ; triangle shape
        cpsl    carrybit
        rrl,r0                  ; shift left with 0 from the carry bit
        brnr,r3 loop1C

        lodi,r3 2
        stra,r3 objectsize      ;  size 2

        lodi,r0 $28             ;  green
        stra,r0 colours12

        lodi,r0 250
        stra,r0 vcb1            ; make sure there are no more duplicates
        lodi,r0 60
        stra,r0 hcb1            ; hcb = 60
        lodi,r0 0
        stra,r0 Obj1dup         ;next to draw is the primary object    
        retc,un

;===================================================================
; subroutine  -  define position of unused objects
             
DefineUnused:
        lodi,r0 254
        stra,r0 vc2         ; push unused objects offscreen
        stra,r0 vc3
        stra,r0 vc4

        lodi,r0 $FF         ; set all objects black
        stra,r0 colours12       
        stra,r0 colours34            
        retc,un