lame.asm

BasicUpstart2(start)

.macro waste_cycles(n) {
    .var nops = floor(n/2)
    .var rem = n&1

    .var c = n
    .if (rem == 0) {
        .for (var i = 0; i < nops; i++) {
            nop
            .eval c -= 2
        }
    } else {
        .for (var i = 0; i < nops-1; i++) {
            nop
            .eval c -= 2
        }
        bit $fe
        .eval c -= 3
    }
    .if (c != 0) {
        .print n
        .print c
        .error "assert"
    }
}

	///////////////////////////////

	*= $4000

start:
	lda #$00
	sta $3fff // Clear border garbage

	// Interrupt
	sei
	lda #<irq
	sta $0314
	lda #>irq
	sta $0315

	lda #$00
	sta $d012
	lda #$01
	sta $d019
	sta $d01a
	lda #$7f
	sta $dc0d

	cli
	jmp *

	///////////////////////////////

irq:
	lda $d019
	and #$01
	sta $d019
	bne cycle
	jmp $ea81

cycle:
	lda $d011
	ora #$08
	sta $d011

	// Let's boogie!
	ldx #$10
	cpx $d012
	bne * - 3

.var x=0
.for (x=0;x<$e4;x++) {
	waste_cycles(63)
}
	lda $d012
	sta $0400 // Results in #$f9... and sometimes $fa

	// Open the bottom border on line $f9
	lda $d011
	and #$f7
	sta $d011

	// Turn off VIC
	lda $d011
	and #%00001000
	sta $d011

	jmp $ea81