mirror of https://github.com/KarolS/millfork.git
138 lines
3.3 KiB
Plaintext
138 lines
3.3 KiB
Plaintext
// ================================================
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//
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// antic_nmien = $40
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//
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// %01000000 $40 VBI
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// %10000000 $80 DLI
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// %11000000 $c0 VBI + DLI
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//
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// ================================================
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//
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// pia_portb = $fe
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//
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// PORTB_BASIC_OFF + PORTB_SELFTEST_OFF + %01111100
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//
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// PORTB_SELFTEST_OFF = %10000000; portb bit value to turn Self-Test off
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// PORTB_BASIC_OFF = %00000010; portb bit value to turn Basic off
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// PORTB_SYSTEM_ON = %00000001; portb bit value to turn System on
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//
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// ================================================
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//
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// Now the routine that lets you get to
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// the RAM that is under the OS.
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// There are actually 2 memory areas
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// present:
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// 4K at $C000 to $CFFF, 49152 to 53247
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// 10K at $D800 to $FFFF, 55296 to 65535
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//
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// The last 6 bytes of the 10K area are not
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// usable, since that is where the interrupt
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// routines are located. Therefore do not
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// use any RAM above $FFF9 (65529) or you
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// will crash the system.
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//
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// ================================================
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byte nmien = $c0
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byte rti @ $15 // default routine for VBI & DLI
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word vbivec @ $10 // vector for VBI
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word vdslst @ $16 // vector for DLI
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// simple display list; LMS = $e000
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const array(byte) dl align(32) = [
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$70,$70,$70,
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$42,$00,$e0,2,2,$f0,2,2,2,$f0,2,2,2,
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$41,@word[dl.addr]
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]
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// init procedure
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void system_off(){
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asm { sei } // turn off IRQ
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antic_nmien = 0 // turn off NMI
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pia_portb = $fe // turn off ROM
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rti = $40 // set RTI opcode
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vbivec = rti.addr // set address for VBI routine
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vdslst = rti.addr // set address for DLI routine
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os_NMIVEC = nmi.addr // set address for custom NMI handler
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antic_nmien = nmien
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}
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// custom NMI handler
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asm void nmi(){
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bit antic_nmist // test nmist
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bpl .vblclock // if 7-bit not set handle VBI
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jmp (vdslst) // indirect jump to DLI routine
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.vblclock: // RTCLOK maintainer
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inc os_RTCLOK.b2
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bne .tickend
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inc os_RTCLOK.b1
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bne .tickend
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inc os_RTCLOK.b0
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.tickend:
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jmp (vbivec) // indirect jump to VBI routine
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}
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// example dli
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interrupt asm void dli_first(){
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pha
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lda #$2a
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sta gtia_colpf2
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sta antic_wsync
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lda #<dli_second.addr
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sta vdslst.lo
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lda #>dli_second.addr
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sta vdslst.hi
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pla
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rti
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}
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// example dli
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interrupt void dli_second(){
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gtia_colpf2 = $de
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antic_wsync = $de
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vdslst = dli_first.addr
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}
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// wait for VBLANK
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asm void pause() {
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lda os_RTCLOK.b2
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.rt_check:
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cmp os_RTCLOK.b2
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beq .rt_check
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rts
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}
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// wait 0-255 frames
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noinline asm void wait(byte register(a) f) {
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clc
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adc os_RTCLOK.b2
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.rt_check:
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cmp os_RTCLOK.b2
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bne .rt_check
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rts
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}
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// example vbi
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interrupt void vbi(){
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gtia_colpf2 = os_RTCLOK.b2
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}
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// main procedure
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void main(){
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system_off() // turn off OS
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wait(100) // waint 2 sec on PAL for fun
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antic_dlist = dl.addr // set custom display list
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wait(100) // waint 2 sec on PAL for the lulz
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vbivec = vbi.addr // set custom VBI
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wait(100) // waint 2 sec on PAL because we can
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vdslst = dli_first.addr // set custom DLI
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while(true){
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wait(100)
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nmien ^= %10000000 // toggle DLI
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antic_nmien = nmien
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}
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}
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