| 84 | } |
| 85 | |
| 86 | void decodeSectorRecord() override |
| 87 | { |
| 88 | if (readRaw24() != APPLE2_SECTOR_RECORD) |
| 89 | return; |
| 90 | |
| 91 | /* Read header. */ |
| 92 | |
| 93 | auto header = toBytes(readRawBits(8 * 8)).slice(0, 8); |
| 94 | ByteReader br(header); |
| 95 | |
| 96 | uint8_t volume = combine(br.read_be16()); |
| 97 | _sector->logicalCylinder = combine(br.read_be16()); |
| 98 | _sector->logicalHead = _ltl->logicalHead; |
| 99 | _sector->logicalSector = combine(br.read_be16()); |
| 100 | uint8_t checksum = combine(br.read_be16()); |
| 101 | |
| 102 | // If the checksum is correct, upgrade the sector from MISSING |
| 103 | // to DATA_MISSING in anticipation of its data record |
| 104 | if (checksum == |
| 105 | (volume ^ _sector->logicalCylinder ^ _sector->logicalSector)) |
| 106 | _sector->status = |
| 107 | Sector::DATA_MISSING; /* unintuitive but correct */ |
| 108 | |
| 109 | if (_sector->logicalHead == 1) |
| 110 | _sector->logicalCylinder -= |
| 111 | _config.apple2().side_one_track_offset(); |
| 112 | |
| 113 | /* Sanity check. */ |
| 114 | |
| 115 | if (_sector->logicalCylinder > 100) |
| 116 | { |
| 117 | _sector->status = Sector::MISSING; |
| 118 | return; |
| 119 | } |
| 120 | } |
| 121 | |
| 122 | void decodeDataRecord() override |
| 123 | { |