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comparison src/vdp.c @ 8:5176efdda5ae

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Initial work on VDP emulation
author Michael Pavone <pavone@retrodev.com>
date Sun, 27 Mar 2016 00:24:31 -0700
parents
children 04d8efe7a1f0
comparison
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7:8f9a05e2e425 8:5176efdda5ae
1 #include <stdint.h>
2 #include <string.h>
3 #include "vdp.h"
4
5 void vdp_init(vdp *context, uint32_t clock_div)
6 {
7 memset(context, 0, sizeof(vdp));
8 context->clock_inc = clock_div;
9 }
10
11 void vdp_run(vdp *context, uint32_t target)
12 {
13 while (context->cycles < target)
14 {
15 context->hcounter++;
16 if (context->hcounter == 416) {
17 context->hcounter = 0;
18 context->vcounter++;
19 if (context->vcounter == 262) {
20 context->vcounter = 0;
21 }
22 }
23 //TODO: do rendering stuff here
24 if (context->status & VDP_STATUS_FIFO) {
25 switch (context->fifo_dest)
26 {
27 case FIFO_DEST_VRAM:
28 if (!(context->status & VDP_STATUS_VRAM)) {
29 context->vram[context->dest_offset++] = context->fifo;
30 context->dest_offset &= sizeof(context->vram)/2-1;
31 context->status &= ~VDP_STATUS_FIFO;
32 }
33 break;
34 case FIFO_DEST_SRAM:
35 if (!(context->status & VDP_STATUS_SRAM)) {
36 context->sram[context->dest_offset++] = context->fifo;
37 context->dest_offset &= sizeof(context->sram)/2-1;
38 context->status &= ~VDP_STATUS_FIFO;
39 }
40 break;
41 case FIFO_DEST_CRAM:
42 context->cram[context->dest_offset++] = context->fifo;
43 context->dest_offset &= sizeof(context->cram)/2-1;
44 context->status &= ~VDP_STATUS_FIFO;
45 break;
46 }
47 }
48 context->cycles += context->clock_inc;
49 }
50 }
51 void vdp_write_address(vdp *context, uint16_t value)
52 {
53 context->status &= ~VDP_STATUS_FIFO;
54 if (value & 0x8000) {
55 context->fifo_dest = FIFO_DEST_VRAM;
56 context->dest_offset = (value & (sizeof(context->vram) -1))/2;
57 } else if (value & 0xFF00 == 0xFE00) {
58 context->fifo_dest = FIFO_DEST_SRAM;
59 context->dest_offset = (value & (sizeof(context->sram) -1))/2;
60 } else if (value & 0xFF00 == 0xFF00) {
61 context->fifo_dest = FIFO_DEST_CRAM;
62 context->dest_offset = (value & (sizeof(context->cram) -1))/2;
63 }
64 }
65
66 void vdp_write_data(vdp *context, uint16_t value)
67 {
68 context->fifo = value;
69 context->status |= VDP_STATUS_FIFO;
70 }