langsmoke/ref_6502

ADC AND ASL BCC BCS BEQ BIT BMI BNE BPL BRA BRK BVC BVS
CLC CLD CLI CLV CMP CPX CPY DEC DEX DEY EOR INC INX INY
JMP JSR LDA LDX LDY LSR NOP ORA PHA PHP PHX PHY PLA PLP
PLX PLY ROL ROR RTI RTS SBC SEC SED SEI STA STP STX STY
STZ TAX TAY TRB TSB TSX TXA TXS TYA WAI
SET     BPL  SETZ
LD      LDA  R0L,X
BK      EQU  *-1
        STA  R0L
        LDA  R0H,X
        STA  R0H
        RTS
ST      LDA  R0L
        STA  R0L,X
        LDA  R0H
        STA  R0H,X
        RTS
STAT    LDA  R0L
STAT2   STA  (R0L,X)
        LDY  $0
STAT3   STY  R14H
INR     INC  R0L,X
        BNE  INR2
        INC  R0H,X
INR2    RTS
LDAT    LDA  (R0L,X)
        STA  R0L
        LDY  $0
        STY  R0H
        BEQ  STAT3
POP     LDY  $0
        BEQ  POP2
POPD    JSR  DCR
        LDA  (R0L,X)
        TAY
POP2    JSR  DCR
        LDA  (R0L,X)
        STA  R0L
        STY  R0H
POP3    LDY  $0
        STY  R14H
        RTS
LDDAT   JSR  LDAT
        LDA  (R0L,X)
        STA  R0H
        JMP  INR
STDAT   JSR  STAT
        LDA  R0H
        STA  (R0L,X)
        JMP  INR
STPAT   JSR  DCR
        LDA  R0L
        STA  (R0L,X)
        JMP  POP3
DCR     LDA  R0L,X
        BNE  DCR2
        DEC  R0H,X
DCR2    DEC  R0L,X
        RTS
SUB     LDY  $0
        CPR  SEC
        LDA  R0L
        SBC  R0L,X
        STA  R0L,Y
        LDA  R0H
        SBC  R0H,X
SUB2    STA  R0H,Y
        TYA
        ADC  $0
        STA  R14H
        RTS
ADD     LDA  R0L
        ADC  R0L,X
        STA  R0L
        LDA  R0H
        ADC  R0H,X
        LDY  $0
        BEQ  SUB2
BS      LDA  R15L
        JSR  STAT2
        LDA  R15H
        JSR  STAT2
BR      CLC
BNC     BCS  BNC2
BR1     LDA  (R15L),Y
        BPL  BR2
        DEY
BR2     ADC  R15L
        STA  R15L
        TYA
        ADC  R15H
        STA  R15H
BNC2    RTS
BC      BCS  BR
        RTS
BP      ASL
        TAX
        LDA  R0H,X
        BPL  BR1
        RTS
BM      ASL
        TAX
        LDA  R0H,X
        BMI  BR1
        RTS
BZ      ASL
        TAX
        LDA  R0L,X
        ORA  R0H,X
        BEQ  BR1
        RTS
BNZ     ASL
        TAX
        LDA  R0L,X
        ORA  R0H,X
        BNE  BR1
        RTS
BM1     ASL
        TAX
        LDA  R0L,X
        AND  R0H,X
        EOR  $FF
        BEQ  BR1
        RTS
BNM1    ASL
        TAX
        LDA  R0L,X
        AND  R0H,X
        EOR  $FF
        BNE  BR1
NUL     RTS
RS      LDX  $18
        JSR  DCR
        LDA  (R0L,X)
        STA  R15H
        JSR  DCR
        LDA  (R0L,X)
        STA  R15L
        RTS
RTN     JMP  RTNZ
	  .org $f000
init:
	  lda  #$00
	  sta  mtalock
	  lda  #$40
	  sta  acr
	  lda  #$c0
	  sta  ier
	  ldy  #0
	  lda  #0
stinit:   sta  $100,y
	  iny
	  bne  stinit
	  lda  #$00
	  sta  mtatask
	  ldy  #maxtask-1
initloop:
	  lda  mtasini,y
	  sta  mtastab,y
	  tax
	  lda  #$b0
	  sta  $0104,x
	  tya
	  asl  a
	  tax
	  stx  mtatemp
	  lda  ent_tab,x
	  ldx  mtastab,y
	  sta  $0105,x
	  ldx  mtatemp
	  lda  ent_tab+1,x
	  ldx  mtastab,y
	  sta  $0106,x
	  dey
	  bpl  initloop
	  ldx  #$3f
	  txs
	  lda  #0
	  sta  t1lsl
	  lda  #40
	  sta  t1csh
	  cli
	  jmp  ent_task0
ent_tab:
	  .word ent_task0
	  .word ent_task1
	  .word ent_task2
	  .word ent_task3
mtaentry:
	  php
	  pha
	  txa
	  pha
	  tya
	  pha
	  tsx
	  inc  $105,x
	  bne  mtaent01
	  inc  $106,x
mtaent01:
	  lda  #$00
	  sta  mtalock
	  jmp  mtaswitch
irq:
	  pha
	  txa
	  pha
	  tya
	  pha
	  lda  t1csl
	  lda  #$c0
	  sta  ifr
	  lda  mtalock
	  beq  mtaswitch
	  inc  mtalock
	  jmp  irq_ret
mtaswitch:
	  ldy  mtatask
	  tsx
	  stx  mtastab,y
	  iny
	  cpy  #maxtask
	  bcc  mtanumok
	  ldy  #0
mtanumok:
	  sty  mtatask
	  ldx  mtastab,y
	  txs
irq_ret:
	  pla
	  tay
	  pla
	  tax
	  pla
	  rti
	  .end