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annotate src/vdp.c @ 11:04d8efe7a1f0

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Initial stab at video output and background color rendering. Fixed address decoding in address port write handler.
author Michael Pavone <pavone@retrodev.com>
date Sun, 27 Mar 2016 17:36:02 -0700
parents 5176efdda5ae
children 04fc17376999
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1 #include <stdint.h>
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2 #include <string.h>
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3 #include "vdp.h"
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4 #include "system.h"
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5
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6 void vdp_init(vdp *context, uint32_t clock_div)
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7 {
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8 memset(context, 0, sizeof(vdp));
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9 //clock div specifies the pixel clock divider
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10 //but our emulation step is half that fast
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11 context->clock_inc = clock_div*2;
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12 context->drawbuffer = context->linebuffers;
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13 context->readbuffer = context->linebuffers+320;
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14 }
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16 void vdp_run(vdp *context, uint32_t target)
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17 {
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18 while (context->cycles < target)
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19 {
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20 context->hcounter+=2;
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21 if (context->hcounter == 416) {
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22 context->hcounter = 0;
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23 context->vcounter++;
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24 if (context->vcounter == 262) {
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25 context->vcounter = 0;
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26 }
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27 }
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28 //TODO: do rendering stuff here
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29 //Draw to framebuffer
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30 if (context->vcounter > 8 && context->vcounter < 249 && context->hcounter < 320) {
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31 if (!context->hcounter && context->vcounter == 9) {
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32 context->framebuffer = system_get_framebuffer(&context->pitch);
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33 //pitch is in terms of bytes, but we want it in terms of pixels
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34 context->pitch /= sizeof(uint16_t);
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35 }
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36 uint16_t *dest = context->framebuffer + (context->vcounter - 9) * context->pitch + context->hcounter;
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37 if (context->status & VDP_STATUS_ENABLED && context->vcounter > 16 && context->vcounter < 241) {
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38 *dest = context->cram[0x3F & context->readbuffer[context->hcounter]];
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39 dest++;
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40 *dest = context->cram[0x3F & context->readbuffer[context->hcounter+1]];
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41 } else {
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42 //Display is disabled or we're in the border area, draw the background color
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43 *dest = *context->cram;
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44 dest++;
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45 *dest = *context->cram;
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46 }
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47 } else if(!context->hcounter && context->vcounter == 249) {
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48 system_framebuffer_updated();
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49 context->framebuffer = NULL;
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50 }
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51 //Handle the FIFO
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52 if (context->status & VDP_STATUS_FIFO) {
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53 switch (context->fifo_dest)
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54 {
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55 case FIFO_DEST_VRAM:
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56 if (!(context->status & VDP_STATUS_VRAM)) {
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57 context->vram[context->dest_offset++] = context->fifo;
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58 context->dest_offset &= sizeof(context->vram)/2-1;
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59 context->status &= ~VDP_STATUS_FIFO;
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60 }
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61 break;
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62 case FIFO_DEST_SRAM:
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63 if (!(context->status & VDP_STATUS_SRAM)) {
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64 context->sram[context->dest_offset++] = context->fifo;
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65 context->dest_offset &= sizeof(context->sram)/2-1;
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66 context->status &= ~VDP_STATUS_FIFO;
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67 }
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68 break;
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69 case FIFO_DEST_CRAM:
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70 context->cram[context->dest_offset++] = context->fifo;
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71 context->dest_offset &= sizeof(context->cram)/2-1;
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72 context->status &= ~VDP_STATUS_FIFO;
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73 break;
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74 }
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75 }
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76 context->cycles += context->clock_inc;
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77 }
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78 }
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79 void vdp_write_address(vdp *context, uint16_t value)
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80 {
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81 context->status &= ~VDP_STATUS_FIFO;
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82 if (!(value & 0x8000)) {
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83 context->fifo_dest = FIFO_DEST_VRAM;
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84 context->dest_offset = (value & (sizeof(context->vram) -1))/2;
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85 } else if ((value & 0xFF00) == 0xFE00) {
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86 context->fifo_dest = FIFO_DEST_SRAM;
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87 context->dest_offset = (value & (sizeof(context->sram) -1))/2;
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88 } else if ((value & 0xFF00) == 0xFF00) {
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89 context->fifo_dest = FIFO_DEST_CRAM;
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90 context->dest_offset = (value & (sizeof(context->cram) -1))/2;
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91 }
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92 }
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93
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94 void vdp_write_data(vdp *context, uint16_t value)
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95 {
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96 context->fifo = value;
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97 context->status |= VDP_STATUS_FIFO;
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98 }