Module spectrusty_formats::mdr

Expand description

MDR file format utilities.

Utilities in this module provide additional methods to the MicroCartridge type with abilities:

to inspect and manipulate sector data on the Microdrive file system level (read, create, erase and list files from cartridges);
to extract files into and from the TAP format;
to write and read MicroCartridge data to and from MDR file format.

MDR files are data images of formatted sectors of ZX Microdrive tape cartridges.

The number of sectors may vary but it will never be a larger than 254.

The last byte determines the write protection flag: if it’s not 0 the cartridge should be protected.

The structure of a single cartridge sector saved in the MDR file:

offset	size	ROM var	description
0	1	HDFLAG	Bit 0 if set indicates a header and should always be set.
1	1	HDNUMB	Sector number: starts from 254 down to 1.
2	2	-	Unknown, probably padding.
4	10	HDNAME	Name of the cartridge with trailing spaces, repeated every formatted sector.
14	1	HDCHK	Checksum of the previous 14 bytes.
15	1	RECFLG	Record flags, see below. Bit 0 should be always reset.
16	1	RECNUM	File block record number: starts at 0.
17	2	RECLEN	File block data length (LSB first), less than or equal to 512.
19	10	RECNAM	Name of the file with trailing spaces, repeated every record.
29	1	DESCHK	Checksum of the previous 14 bytes.
30	512	CHDATA	Record block data: 0..RECLEN.
542	1	DCHK	Checksum of the previous 512 bytes, regardless of RECLEN value.

Record flags (RECFLG):

Bit 0 is always reset to indicate a record block descriptor.
Bit 1 is set for the last record block (End Of File).
Bit 2 is set for regular files and reset if the record is part of a PRINT type file (a stream).

The above structure and ROM variable names are from the book by Gianluca Carri “Spectrum Shadow ROM Disassembly”.

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