Spectrum emulator file format: udi
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Track data format 
Edit
Offset Length Comment 0x0000 1 Track type 0x00 - MFM data 0x01 - FM data 0x02 - mixed MFM/FM data 0x80 - 'floating' or 'weak' MFM data 0x81 - 'floating' or 'weak' FM data 0x82 - 'floating' or 'weak' mixed MFM/FM data 0x83 - 'floating' or 'weak' data with multiple read 0xe0 - microdrive 'track' 0xf0 - zlib 'compressed' track container 0x03-0x7f and 0x81-0xef reserved 0xf1-0xff reserved for other compressions (e.g. bzip2 and lzma)
0x0001 TDATAL Track data as described later
- TRLENN = 1 + TDATALN
Track data for type 0x00 (MFM) and 0x01 (FM) Edit
Offset Length Comment 0x0000 2 TLEN Track data size in bytes include MARKs GAPs etc.
0x0002 TLEN Data bytes 0x0002 + TLEN CLEN Track clock marks where CLEN = TLEN / 8 + ( TLEN % 8 + 7 ) / 8 One bit corresponds with one byte of raw track data 0 - byte with normal CLK (normal data) 1 - byte with mark CLK (for index label 0xA1 ¨ 0xC2) For example: { 0xA1,0xA1,0x00,0xA1,0xFE,0x00,0x00,0x01 } where 0xA1 - MFM markers for this raw data, bits array store as one byte - 0x0B unused last bits should be 0.
- TDATALN = 2 + TLENN + CLENN
Track data for type 0x02 (mixed MFM/FM) Edit
Offset Length Comment 0x0000 2 TLEN Track data size in bytes include MARKs GAPs etc.
0x0002 TLEN Data bytes 0x0002 + TLEN CLEN Track clock marks where CLEN = TLEN / 8 + ( TLEN % 8 + 7 ) / 8 One bit corresponds with one byte of raw track data 0 - byte with normal CLK (normal data) 1 - byte with mark CLK (for index label 0xA1 ¨ 0xC2) For example: { 0xA1,0xA1,0x00,0xA1,0xFE,0x00,0x00,0x01 } where 0xA1 - MFM markers for this raw data, bits array store as one byte - 0x0B unused last bits should be 0.0x0002 + TLEN + CLEN MLEN MF marks where MLEN = CLEN One bit corresponds with one byte of raw track data 0 - byte coded with MFM 1 - byte code with FM unused last bits should be 0.
- TDATALN = 2 + TLENN + 2×CLENN
Track data for type 0x80 (MFM) or 0x81 (FM) "floating" or "weak" data chunk Edit
Offset Length Comment 0x0000 2 TLEN Track data size in bytes include MARKs GAPs etc.
0x0002 TLEN Data bytes 0x0002 + TLEN CLEN Track clock marks where CLEN = TLEN / 8 + ( TLEN % 8 + 7 ) / 8 One bit corresponds with one byte of raw track data 0 - byte with normal CLK (normal data) 1 - byte with mark CLK (for index label 0xA1 ¨ 0xC2) For example: { 0xA1,0xA1,0x00,0xA1,0xFE,0x00,0x00,0x01 } where 0xA1 - MFM markers for this raw data, bits array store as one byte - 0x0B unused last bits should be 0.0x0002 + TLEN + CLEN FLEN Float marks where FLEN = CLEN One bit corresponds with one byte of raw track data 0 - byte not 'floating' ( not 'weak') 1 - byte 'floating' ('weak') unused last bits should be 0.
- TDATALN = 2 + TLENN + 2×CLENN
Track data for type 0x82 (mixed MFM/FM) "floating" or "weak" data chunk Edit
Offset Length Comment 0x0000 2 TLEN Track data size in bytes include MARKs GAPs etc.
0x0002 TLEN Data bytes 0x0002 + TLEN CLEN Track clock marks where CLEN = TLEN / 8 + ( TLEN % 8 + 7 ) / 8 One bit corresponds with one byte of raw track data 0 - byte with normal CLK (normal data) 1 - byte with mark CLK (for index label 0xA1 ¨ 0xC2) For example: { 0xA1,0xA1,0x00,0xA1,0xFE,0x00,0x00,0x01 } where 0xA1 - MFM markers for this raw data, bits array store as one byte - 0x0B unused last bits should be 0.0x0002 + TLEN + CLEN MLEN MF marks where MLEN = CLEN One bit corresponds with one byte of raw track data 0 - byte coded with MFM 1 - byte code with FM unused last bits should be 0.
0x0002 + TLEN + 2 * CLEN FLEN Float marks where FLEN = CLEN One bit corresponds with one byte of raw track data 0 - byte not 'floating' ( not 'weak') 1 - byte 'floating' ('weak') unused last bits should be 0.
- TDATALN = 2 + TLENN + 3×CLENN
Track data for type 0x83 ("floating" or "weak" data chunk with multiple 'read') Edit
Offset Length Comment 0x0000 2 TLEN + (NUM - 1) Track data size in bytes include MARKs GAPs etc. TLEN must be aligned to 8, so the lowest 3 bit always 0. NUM must be between 1 and 8.
0x0002 2 OFFS / 8 OFFSet from the start of the previouse Track OFFS aligned to 8.
0x0004 TLEN First alternate, Data bytes 0x0004 + TLEN CLEN First alternative, Track clock marks where CLEN = TLEN / 8 One bit corresponds with one byte of raw track data 0 - byte with normal CLK (normal data) 1 - byte with mark CLK (for index label 0xA1 ¨ 0xC2) For example: { 0xA1,0xA1,0x00,0xA1,0xFE,0x00,0x00,0x01 } where 0xA1 - MFM markers for this raw data, bits array store as one byte - 0x0B start and length are 8 bit aligned, so there are no unused bits.0x0004 + TLEN + CLEN TLEN Second alternative, Data bytes 0x0004 + 2 × TLEN + CLEN CLEN Second alernative, Track clock marks ... continues until all data chunk ...
- TDATALN = 4 + TLENN + CLENN
- where TLEN = (TLEN + (NUM - 1)) & 0xfff8
- where NUM = ((TLEN + (NUM - 1)) & 0x0007) + 1
- This track data is represent "alternative" read of the given part (OFFS, TLEN) of the previouse track (type: 0x00, 0x01 or 0x02)
- This track must be preceeded by a full track (type: 0x00, 0x01 or 0x02). We can define several not overlapped alternative read areas. e.g.:
- TrackN data (0x00); 3 × TrackN,offs1,len1; 2 × TrackN,offs2,len2</sub>; TrackN+1 data(0x00); e.t.c.
####### TrackN data (type: 0x00) ######## ## TrackN,offs1,len1-1 ## ## TrackN,offs1,len1-2 ## ## TrackN,offs1,len1-3 ## ## TrackN,offs2,len2-1 ## ## TrackN,offs2,len2-2 ## ####### TrackN+1 data (type: 0x00) ########
Track data for type 0xe0 Microdrive cartridge track Edit
Offset Length Comment 0x0000 2 TLEN / 8 Track data size in bytes include GAPs etc.
0x0002 TLEN Data bytes 0x0002 + TLEN BLEN Track bad bytes marks where BLEN = TLEN / 8 One bit corresponds with one byte of raw track data 0 - byte usable 1 - byte unusable (bad)
- TDATALN = 2 + TLENN
- Note: on Microdrive tapes the data recorded in two paralell tracks (with a standard stereo
- tape head arrangement), but the Interface I hardware deal about multiplexing/demultiplexing
- data so, ZX Spectrum never see the two track separately.
- Note2: the track length is always 8 byte aligned, so if your data cannot fit on an 8 byte boundary, you must pad with unusable bytes. This is not unnatural because where the microdrive endless tape spliced there are several bad bytes.
Data for type 0xf0 ("compressed" track data) Edit
Offset Length Comment 0x0000 2 DLEN - 1 Compressed data size minus one.
0x0002 1 Track type This is the track type of uncompressed data, so emulators can calculate uncompressed length and make decision about the track without uncompressing the data (e.g. discard weak track data if it not supported, etc...)
0x0003 2 TLEN This is the TLEN of uncompressed data, so emulators can calculate uncompressed length
0x0005 DLEN Data bytes. If uncompress this data with zlib it gives track data as defined in Tracks data without Track type and TLEN.
- TDATALN = 6 + DLENN
- This track is a container which hold headerless track data in a compressed way.
- So after uncompression, we get a whole track without Track type and TLEN
- as defined in Tracks data.
- Only 0x00, 0x01, 0x02, 0x80, 0x81, 0x82 and 0x83 are the valid Track types, so
- compressed tracks cannot be nested.
- Compression method is the zlib deflate algorithm with standard zlib header.
- Uncompressed data length can be calculated from Track type and TLEN
- according to section Track data for type 0x00 (MFM) and 0x01 (FM)
- For e.g. if Track Type is 0x00 (MFM track), then track length is
- TDATAL = 3 + TLEN + TLEN / 8 + (TLEN % 8 + 7) / 8 and uncompressed data
- length is TDATAL - 3 (because compressed data does not include Track type and TLEN.
- Note: The compressed size maximum is 65536 byte, so if a track compressed size grater than
- 65536 it can be recorded only as uncompressed track.
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