SixtyPical/doc/Emitting.markdown

Emitting Ophis from SixtyPical Programs

-> Tests for functionality "Emit ASM for SixtyPical program"

-> Functionality "Emit ASM for SixtyPical program" is implemented by
-> shell command "bin/sixtypical emit %(test-file)"

Emitting an if.

| assign byte screen $0400
| routine main {
|    lda screen
|    cmp screen
|    if beq {
|        tax
|    } else {
|        tay
|    }
|    sta screen
| }
= main:
=   lda screen
=   cmp screen
=   BEQ _label_1
=   tay
=   jmp _past_1
= _label_1:
=   tax
= _past_1:
=   sta screen
=   rts
= 
= .alias screen 1024

Emitting a repeat.

| assign byte screen 1024
| reserve byte zero
| routine main {
|    ldy zero
|    repeat bne {
|       inc screen
|       dey
|       cpy zero
|    }
|    sty screen
| }
= main:
=   ldy zero
=   
= _repeat_1:
=   inc screen
=   dey
=   cpy zero
=   BNE _repeat_1
=   sty screen
=   rts
= 
= .alias screen 1024
= zero: .byte 0

Nested ifs.

| routine main {
|   if beq {
|     if bcc {
|       lda #0
|     } else {
|       if bvs {
|         lda #1
|       } else {
|         lda #2
|       }
|     }
|   } else {
|     lda #3
|   }
| }
= main:
=   BEQ _label_3
=   lda #3
=   jmp _past_3
= _label_3:
=   BCC _label_2
=   BVS _label_1
=   lda #2
=   jmp _past_1
= _label_1:
=   lda #1
= _past_1:
=   jmp _past_2
= _label_2:
=   lda #0
= _past_2:
= _past_3:
=   rts

Installing an interrupt handler (at the Kernal level, i.e. with CINV)

| assign byte screen 1024
| assign vector cinv 788
| reserve vector save_cinv
| 
| routine main {
|   sei {
|     copy vector cinv to save_cinv
|     copy routine our_cinv to cinv
|   }
| }
| 
| routine our_cinv {
|   inc screen
|   jmp save_cinv
| }
= main:
=   sei
=   lda cinv
=   sta save_cinv
=   lda cinv+1
=   sta save_cinv+1
=   lda #<our_cinv
=   sta cinv
=   lda #>our_cinv
=   sta cinv+1
=   cli
=   rts
= 
= our_cinv:
=   inc screen
=   jmp (save_cinv)
=   rts
= 
= .alias screen 1024
= .alias cinv 788
= save_cinv: .word 0