OXYGENHUB
◆ main openmsx / src / fdc / Disk.cc
4.1 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
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#include "Disk.hh"
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#include "DiskExceptions.hh"
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#include "narrow.hh"
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#include "one_of.hh"
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namespace openmsx {
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Disk::Disk(DiskName name_)
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	: name(std::move(name_))
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{
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}
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void Disk::writeTrack(uint8_t track, uint8_t side, const RawTrack& input)
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{
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	if (isWriteProtected()) {
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		throw WriteProtectedException();
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	}
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	writeTrackImpl(track, side, input);
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	flushCaches();
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}
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bool Disk::isDoubleSided()
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{
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	if (!nbSides) {
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		detectGeometry();
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	}
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	return nbSides == 2;
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}
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// Note: Special case to convert between logical/physical sector numbers
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//       for the boot sector and the 1st FAT sector (logical sector: 0/1,
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//       physical location: track 0, side 0, sector 1/2): perform this
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//       conversion without relying on the detected geometry parameters.
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//       Otherwise the detectGeometry() method (which itself reads these
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//       two sectors) would get in an infinite loop.
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size_t Disk::physToLog(uint8_t track, uint8_t side, uint8_t sector)
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{
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	if ((track == 0) && (side == 0)) {
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		return sector - 1;
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	}
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	if (!nbSides) {
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		detectGeometry();
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	}
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	return sectorsPerTrack * (side + nbSides * track) + (sector - 1);
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}
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Disk::TSS Disk::logToPhys(size_t log)
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{
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	if (log <= 1) {
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		uint8_t track = 0;
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		uint8_t side = 0;
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		auto sector = narrow<uint8_t>(log + 1);
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		return {.track = track, .side = side, .sector = sector};
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	}
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	if (!nbSides) {
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		detectGeometry();
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	}
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	auto track  = narrow<uint8_t>(log / (size_t(nbSides) * sectorsPerTrack));
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	auto side   = narrow<uint8_t>((log / sectorsPerTrack) % nbSides);
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	auto sector = narrow<uint8_t>((log % sectorsPerTrack) + 1);
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	return {.track = track, .side = side, .sector = sector};
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}
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unsigned Disk::getSectorsPerTrack()
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{
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	if (!nbSides) {
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		detectGeometry();
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	}
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	return sectorsPerTrack;
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}
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void Disk::detectGeometryFallback() // if all else fails, use statistics
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{
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	// TODO maybe also check for 8*80 for 8 sectors per track
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	sectorsPerTrack = 9; // most of the time (sorry 5.25" disk users...)
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	// 360k disks are likely to be single sided:
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	nbSides = (getNbSectors() == 720) ? 1 : 2;
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}
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void Disk::detectGeometry()
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{
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	// From the MSX Red Book (p265):
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	//
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	//  How to determine media types
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	//
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	//  a) Read the boot sector (track 0, sector 1) of the target drive
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	//
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	//  b) Check if the first byte is either 0E9H or 0EBH (the JMP
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	//     instruction on 8086)
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	//
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	//  c) If step b) fails, the disk is a version prior to MS-DOS 2.0;
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	//     therefore, use the first byte of the FAT passed from the caller
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	//     and make sure it is between 0F8h and 0FFh.
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	//
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	//     If step c) is successful, use this as a media descriptor.
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	//     If step c) fails, then this disk cannot be read.
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	//
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	//  d) If step b) succeeds, read bytes # 0B to # 1D. This is the
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	//     DPB for MS-DOS, Version 2.0 and above. The DPB for MSX-DOS can
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	//     be obtained as follows.
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	//
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	//     ....
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	//     +18 +19  Sectors per track
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	//     +1A +1B  Number of heads
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	//     ...
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	//
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	//     Media Descriptor  0F8H  0F9H  0FAh  0FBH  0FCH  0FDH  0FEH  0FFH
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	//       byte (FAT-ID)
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	//     Sectors/track        9     9     8     8     9     9     8     8
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	//     No. of sides         1     2     1     2     1     2     1     2
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	//     Tracks/side         80    80    80    80    40    40    40    40
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	//     ...
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	try {
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		SectorBuffer buf;
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		readSector(0, buf); // boot sector
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		if (buf.raw[0] == one_of(0xE9, 0xEB)) {
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			// use values from boot sector
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			sectorsPerTrack = buf.bootSector.sectorsTrack;
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			nbSides         = buf.bootSector.nrSides;
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			if ((sectorsPerTrack == 0) || (sectorsPerTrack > 255) ||
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			    (nbSides         == 0) || (nbSides         > 255)) {
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				// seems like bogus values, use defaults
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				detectGeometryFallback();
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			}
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		} else {
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			readSector(1, buf); // 1st fat sector
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			auto mediaDescriptor = buf.raw[0];
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			if (mediaDescriptor >= 0xF8) {
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				sectorsPerTrack = (mediaDescriptor & 2) ? 8 : 9;
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				nbSides         = (mediaDescriptor & 1) ? 2 : 1;
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			} else {
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				// invalid media descriptor, just assume it's a
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				// normal DS or SS DD disk
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				detectGeometryFallback();
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			}
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		}
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	} catch (MSXException&) {
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		// read error, assume it's a 3.5" DS or SS DD disk
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		detectGeometryFallback();
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	}
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}
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} // namespace openmsx