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annotate system.c @ 1503:a763523dadf4 segacd

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Added code for initializing a combined Genesis + Sega CD system when a Sega CD ISO is loaded
author Michael Pavone <pavone@retrodev.com>
date Wed, 13 Dec 2017 09:44:41 -0800
parents aee2177a1630
children 5dacaef602a7
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1 #include <string.h>
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2 #include "system.h"
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3 #include "genesis.h"
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4 #include "sms.h"
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5
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6 uint8_t safe_cmp(char *str, long offset, uint8_t *buffer, long filesize)
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7 {
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8 long len = strlen(str);
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9 return filesize >= offset+len && !memcmp(str, buffer + offset, len);
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10 }
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11
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12 system_type detect_system_type(system_media *media)
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13 {
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14 if (safe_cmp("SEGA", 0x100, media->buffer, media->size)) {
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15 //TODO: support other bootable identifiers
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16 if (safe_cmp("SEGADISCSYSTEM", 0, media->buffer, media->size)) {
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17 return SYSTEM_SEGACD;
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18 }
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19 //TODO: Differentiate between vanilla Genesis and 32X games
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20 return SYSTEM_GENESIS;
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21 }
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22 if (safe_cmp("TMR SEGA", 0x1FF0, media->buffer, media->size)
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23 || safe_cmp("TMR SEGA", 0x3FF0, media->buffer, media->size)
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24 || safe_cmp("TMR SEGA", 0x7FF0, media->buffer, media->size)
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25 ) {
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26 return SYSTEM_SMS;
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27 }
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28 //TODO: Detect Jaguar ROMs here
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29
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30 //Header based detection failed, examine filename for clues
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31 if (media->extension) {
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32 if (!strcmp("md", media->extension) || !strcmp("gen", media->extension)) {
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33 return SYSTEM_GENESIS;
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34 }
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35 if (!strcmp("sms", media->extension)) {
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36 return SYSTEM_SMS;
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37 }
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38 if (!strcmp("j64", media->extension)) {
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39 return SYSTEM_JAGUAR;
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40 }
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41 }
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42
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43 //More certain checks failed, look for a valid 68K reset vector
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44 if (media->size >= 8) {
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45 char *rom = media->buffer;
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46 uint32_t reset = rom[4] << 24 | rom[5] << 16 | rom[6] << 8 | rom[7];
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47 if (!(reset & 1) && reset < media->size) {
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48 //we have a valid looking reset vector, assume it's a Genesis ROM
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49 return SYSTEM_GENESIS;
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50 }
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51 }
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52 return SYSTEM_UNKNOWN;
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53 }
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54
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55 system_header *alloc_config_system(system_type stype, system_media *media, uint32_t opts, uint8_t force_region, rom_info *info_out)
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56 {
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57 void *lock_on = NULL;
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58 uint32_t lock_on_size = 0;
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59 if (media->chain) {
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60 lock_on = media->chain->buffer;
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61 lock_on_size = media->chain->size;
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62 }
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63 switch (stype)
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64 {
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65 case SYSTEM_GENESIS:
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66 return &(alloc_config_genesis(media->buffer, media->size, lock_on, lock_on_size, opts, force_region, info_out))->header;
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67 case SYSTEM_SEGACD:
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68 return &(alloc_config_genesis_cdboot(media, opts, force_region, info_out))->header;
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69 #ifndef NO_Z80
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70 case SYSTEM_SMS:
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71 return &(alloc_configure_sms(media, opts, force_region, info_out))->header;
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72 #endif
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73 default:
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74 return NULL;
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75 }
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76 }