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