Andrew Davie wrote:
> Anyway, Thomas... how about it? How about sharing those areas where you
> feel you *must* use the illegal opcodes and let those of us who are on
> higher moral ground :)) tell you why you don't need to :)
Ok, actually the score-displaying routine is the only place where i
really need the illegal opcodes.
I used them get some free time (16 cycles) for other effects. The
result is actually only a *47* pixel routine, because the right pixel
of the first and the third digit (if i remember it correct) are always
the same. That works for me, the score display has blank pixels there,
and THRUST too (except for the long T-line). Here is the result:
..digitLoop:
nop ; 2 61
nop ; 2 63
nop ; 2 65
nop ; 2 67
nop ; 2 69
nop ; 2 71
nop ; 2 73
nop ; 2 75
lda (digitPtr+$a),y ; 5 4
sta GRP0 ; 3 7
lda (digitPtr+$8),y ; 5 12
sta GRP1 ; 3 15
lda (digitPtr+$6),y ; 5 20
sta GRP0 ; 3 23
lax (digitPtr+$0),y ; 5 28 illegal
txs ; 2 30
lax (digitPtr+$4),y ; 5 35 illegal
lda (digitPtr+$2),y ; 5 40
stx GRP1 ; 3 43
sta GRP0 ; 3 46
tsx ; 2 48
stx GRP1 ; 3 51
sty GRP0 ; 3 54
dey ; 2 56
bpl .digitLoop ; 2³ 59
As you can see, i saved the time by using LAX and the stack pointer.
Then i added the color-scrolling effect, wasted some time (AND, TYA) to
get the code working for my needs, and that's how it looks like now:
..digitLoop:
dey ; 2 61
lda (digcolPtr),y ; 5 66
and digcolMask ; 3 69
sta COLUP0 ; 3 72
sta COLUP1 ; 3 75
lda (digitPtr+$a),y ; 5 4
sta GRP0 ; 3 7
lda (digitPtr+$8),y ; 5 12
sta GRP1 ; 3 15
lda (digitPtr+$6),y ; 5 20
sta GRP0 ; 3 23
lax (digitPtr+$0),y ; 5 28 illegal
txs ; 2 30
lax (digitPtr+$4),y ; 5 35 illegal
lda (digitPtr+$2),y ; 5 40
stx GRP1 ; 3 43
sta GRP0 ; 3 46
tsx ; 2 48
stx GRP1 ; 3 51
sty GRP0 ; 3 54
tya ; 2 56
bne .digitLoop ; 2³ 59 when loop ends: y=0
There are a few other places in the code where i saved some bytes and
cycles with illegal opcodes (LAX to get a value in two registers, a
long NOP instead of BIT to skip one instruction and keep the flags,...),
but i could make them legal again.
Thomas Jentzsch | *** Every bit is sacred ! ***
tjentzsch at web dot de |
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