certain-6502

This program is not meant to build. What the tool says is the lesson.

NGA5107 `jra` is a `65sc02` instruction, and this target is a `6502` /Users/waldek/Desktop/NGA/tutorial/12-instructions/certain/jump.asm:29

NGA5107 `jra` is a `65sc02` instruction, and this target is a `6502` /Users/waldek/Desktop/NGA/tutorial/12-instructions/certain/jump.asm:32

main.ngp

target { region $0080 .. $00FF ram   region $2000 .. $BFFF ram }
modules { "../certain/jump.asm" }
container raw

jump.asm jump

.section
flag
        .res 1
.ends

.macro unrolled n
.if n > 0
        lda flag
        clc
        adc #7
        sta flag
        unrolled n - 1
.endif
.endm

; tag certain
; Four jumps that are always taken, and none of them five bytes: there is no
; opposite branch and nothing to skip. The `clc` above each `jmpcc` is what
; makes the claim true; `jra` claims nothing and needs no such line.
.proc entry
        clc
@a      jmpcc @near
@b      inc flag
@near
        clc
@c      jmpcc @far
@d      unrolled 16
@far
@e      jra @beyond
@f      inc flag
@beyond
@g      jra @end
@h      unrolled 16
@end
        rts

        .assert @b - @a == 2
        .assert @d - @c == 3
        .assert @f - @e == 2
        .assert @h - @g == 3
.endp
; end certain