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https://github.com/hsoft/collapseos.git
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83 lines
2.1 KiB
C
83 lines
2.1 KiB
C
#include <string.h>
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#include "vdp.h"
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void vdp_init(VDP *vdp)
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{
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memset(vdp->vram, 0, VDP_VRAM_SIZE);
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memset(vdp->regs, 0, 0x10);
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vdp->has_cmdlsb = false;
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vdp->curaddr = 0;
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}
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uint8_t vdp_cmd_rd(VDP *vdp)
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{
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return 0;
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}
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void vdp_cmd_wr(VDP *vdp, uint8_t val)
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{
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if (!vdp->has_cmdlsb) {
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vdp->cmdlsb = val;
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vdp->has_cmdlsb = true;
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return;
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}
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vdp->has_cmdlsb = false;
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if ((val & 0xc0) == 0x80) {
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// set register
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vdp->regs[val&0xf] = vdp->cmdlsb;
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} else if ((val & 0xc0) == 0xc0) {
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// palette RAM
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vdp->curaddr = 0x4000 + (vdp->cmdlsb&0x1f);
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} else {
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// VRAM
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vdp->curaddr = ((val&0x3f) << 8) + vdp->cmdlsb;
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}
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}
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uint8_t vdp_data_rd(VDP *vdp)
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{
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uint8_t res = vdp->vram[vdp->curaddr];
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if (vdp->curaddr < VDP_VRAM_SIZE) {
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vdp->curaddr++;
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}
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return res;
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}
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void vdp_data_wr(VDP *vdp, uint8_t val)
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{
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vdp->vram[vdp->curaddr] = val;
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if (vdp->curaddr < VDP_VRAM_SIZE) {
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vdp->curaddr++;
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}
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}
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// Returns a 8-bit RGB value (0b00bbggrr)
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uint8_t vdp_pixel(VDP *vdp, uint16_t x, uint16_t y)
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{
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if (x >= VDP_SCREENW) {
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return 0;
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}
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if (y >= VDP_SCREENH) {
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return 0;
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}
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// name table offset
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uint16_t offset = 0x3800 + ((y/8) << 6) + ((x/8) << 1);
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uint16_t tableval = vdp->vram[offset] + (vdp->vram[offset+1] << 8);
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uint16_t tilenum = tableval & 0x1ff;
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// is palette select bit on? if yes, use sprite palette instead
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uint8_t palettemod = tableval & 0x800 ? 0x10 : 0;
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// tile offset this time. Each tile is 0x20 bytes long.
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offset = tilenum * 0x20;
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// Each 4 byte is a row. Find row first.
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offset += ((y%8) * 4);
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uint8_t bitnum = 7 - (x%8);
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// Now, let's compose the result by pushing the right bit of our 4 bytes
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// into our result.
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uint8_t palette_id = ((vdp->vram[offset] >> bitnum) & 1) + \
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(((vdp->vram[offset+1] >> bitnum) & 1) << 1) + \
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(((vdp->vram[offset+2] >> bitnum) & 1) << 2) + \
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(((vdp->vram[offset+3] >> bitnum) & 1) << 3);
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uint8_t rgb = vdp->vram[0x4000+palettemod+palette_id];
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return rgb;
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}
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