// license:BSD-3-Clause // copyright-holders:Dirk Best /*************************************************************************** JVC Disk image format Used by Jeff Vavasour's CoCo Emulators Documentation taken from Tim Lindner's web site: http://tlindner.macmess.org/?page_id=86 A. Header length The header length is determined by the file length modulo 256: headerSize = fileLength % 256; This means that the header is variable length and the minimum size is zero bytes, and the maximum size of 255 bytes. B. Header Here is a description of the header bytes: Byte Offset Description Default ----------- ----------- ------- 0 Sectors per track 18 1 Side count 1 2 Sector size code 1 3 First sector ID 1 4 Sector attribute flag 0 If the sector attribute flag is zero then the track count is determined by the formula: (fileLength - headerSize) / (sectorsPerTrack * (128 << sectorSizeCode)) / sideCount If the sector attribute flag is non zero then the track count is determined by the more complex formula: (fileLength - headerSize) / (sectorsPerTrack * ((128 << sectorSizeCode) + 1) ) / sideCount If the length of the header is to short to contain the geometry desired, then the default values are assumed. If the header length is zero the all of the geometry is assumed. When creating disk images it is desirable to make the header length as short as possible. The header should only be used to deviate from the default values. The sector data begins immediately after the header. If the header length is zero then the sector data is at the beginning file. C. Sectors per track This is the number of sectors per track (ones based). A value of 18 means there are 18 sectors per track D. Side Count This is the number of sides in the disk image. Values of 1 or 2 are acceptable. If there are two sides then the tracks are interleaved. The first track in the image file is track zero side 1, the second track in the image file is track zero side 2. E. Sector size The is the same value that is stored in the wd179x ID field to determine sector size: 0x00 128 bytes 0x01 256 bytes 0x02 512 bytes 0x03 1024 bytes Other values are undefined. Every sector in the disk image must be the same size. F. First sector ID This determines the first sector ID for each track. Each successive sector adds one to the previous ID. If the first sector ID is 1, then the second sector has an ID of 2, and the third has an ID of 3. G. Sector Attribute Flag If this byte is non zero, then each sector contains an additional byte prepended to the sector data. If the attribute flag is zero then there are no extra bytes in front of the sector data. H. Sector attribute byte This byte is put at the beginning of every sector if the header flag is turned on. The information this byte contains is the same as the status register (of the wd179x) would contain when a 'Read Sector' command was issued. The bit fields are defined as: Bit position: --------------- 7 6 5 4 3 2 1 0 | | | | | | | | | | | | | | | +--- Not used. Set to zero. | | | | | | +----- Not used. Set to zero. | | | | | +------- Not used. Set to zero. | | | | +--------- Set on CRC error. | | | +----------- Set if sector not found. | | +------------- Record type: 1 - Deleted Data Mark, 0 - Data Mark. | +--------------- Not Used. Set to zero. +----------------- Not Used. Set to zero. TODO: - Support writing unusual formats? ***************************************************************************/ #include "jvc_dsk.h" #include "ioprocs.h" #include "osdcore.h" // osd_printf_* jvc_format::jvc_format() { } const char *jvc_format::name() const noexcept { return "jvc"; } const char *jvc_format::description() const noexcept { return "JVC disk image"; } const char *jvc_format::extensions() const noexcept { return "jvc,dsk"; } bool jvc_format::parse_header(util::random_read &io, int &header_size, int &tracks, int &heads, int §ors, int §or_size, int &base_sector_id) { // The JVC format has a header whose size is the size of the image modulo 256. Currently, we only // handle up to five header bytes uint64_t size; if (io.length(size) || !size) return false; header_size = size % 256; uint8_t header[5]; // if we know that this is a header of a bad size, we can fail immediately; otherwise read the header if (header_size >= sizeof(header)) // TODO: wouldn't this make more sense with > than >=? The first case in the following switch statement is unreachable as-is. return false; if (header_size > 0) { auto const [err, actual] = read_at(io, 0, header, header_size); if (err || (actual != header_size)) return false; } // default values heads = 1; sectors = 18; sector_size = 256; base_sector_id = 1; switch (header_size) { case 5: osd_printf_info("jvc_format: sector attribute flag unsupported\n"); return false; case 4: base_sector_id = header[3]; [[fallthrough]]; case 3: sector_size = 128 << header[2]; [[fallthrough]]; case 2: heads = header[1]; [[fallthrough]]; case 1: sectors = header[0]; [[fallthrough]]; case 0: tracks = (size - header_size) / sector_size / sectors / heads; break; } if (tracks > 82) { osd_printf_info("jvc_format: track count of %d unsupported\n", tracks); return false; } osd_printf_verbose("jvc_format: Floppy disk image geometry: %d tracks, %d head(s), %d sectors with %d bytes.\n", tracks, heads, sectors, sector_size); return tracks * heads * sectors * sector_size == (size - header_size); } int jvc_format::identify(util::random_read &io, uint32_t form_factor, const std::vector &variants) const { int header_size, tracks, heads, sectors, sector_size, sector_base_id; if (parse_header(io, header_size, tracks, heads, sectors, sector_size, sector_base_id)) return FIFID_SIZE; else return 0; } bool jvc_format::load(util::random_read &io, uint32_t form_factor, const std::vector &variants, floppy_image &image) const { int header_size, track_count, head_count, sector_count, sector_size, sector_base_id; int max_tracks, max_heads; if (!parse_header(io, header_size, track_count, head_count, sector_count, sector_size, sector_base_id)) return false; // safety check if (sector_count * sector_size > 10000) { osd_printf_error("jvc_format: incorrect track layout\n"); return false; } image.get_maximal_geometry(max_tracks, max_heads); if (track_count > max_tracks) { osd_printf_error("jvc_format: Floppy disk has too many tracks for this drive (floppy tracks=%d, drive tracks=%d).\n", track_count, max_tracks); return false; } if (head_count > max_heads) { osd_printf_error("jvc_format: Floppy disk has too many sides for this drive (floppy sides=%d, drive sides=%d).\n", head_count, max_heads); return false; } int file_offset = header_size; for (int track = 0; track < track_count; track++) { for (int head = 0; head < head_count ; head++) { desc_pc_sector sectors[256]; uint8_t sector_data[10000]; int sector_offset = 0; // standard RS-DOS interleave static constexpr int interleave[18] = { 0, 11, 4, 15, 8, 1, 12, 5, 16, 9, 2, 13, 6, 17, 10, 3, 14, 7 }; for (int i = 0; i < sector_count; i++) { sectors[interleave[i]].track = track; sectors[interleave[i]].head = head; sectors[interleave[i]].sector = sector_base_id + i; sectors[interleave[i]].actual_size = sector_size; sectors[interleave[i]].size = sector_size >> 8; sectors[interleave[i]].deleted = false; sectors[interleave[i]].bad_crc = false; sectors[interleave[i]].data = §or_data[sector_offset]; /*auto const [err, actual] =*/ read_at(io, file_offset, sectors[interleave[i]].data, sector_size); // FIXME: check for errors and premature EOF sector_offset += sector_size; file_offset += sector_size; } build_wd_track_mfm(track, head, image, 100000, sector_count, sectors, 22, 32, 24); } } return true; } bool jvc_format::save(util::random_read_write &io, const std::vector &variants, const floppy_image &image) const { uint64_t file_offset = 0; int track_count, head_count; image.get_actual_geometry(track_count, head_count); // we'll write a header if the disk is two-sided if (head_count == 2) { uint8_t header[2]; header[0] = 18; header[1] = 2; /*auto const [err, actual] =*/ write_at(io, file_offset, header, sizeof(header)); // FIXME: check for errors file_offset += sizeof(header); } // write disk data for (int track = 0; track < track_count; track++) { for (int head = 0; head < head_count; head++) { auto bitstream = generate_bitstream_from_track(track, head, 2000, image); auto sectors = extract_sectors_from_bitstream_mfm_pc(bitstream); for (int i = 0; i < 18; i++) { if (sectors[1 + i].size() != 256) { osd_printf_error("jvc_format: invalid sector size: %d\n", sectors[1 + i].size()); return false; } /*auto const [err, actual] =*/ write_at(io, file_offset, sectors[1 + i].data(), 256); // FIXME: check for errors file_offset += 256; } } } return true; } bool jvc_format::supports_save() const noexcept { return true; } const jvc_format FLOPPY_JVC_FORMAT;