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Partially complete rework of all the decoders to avoid seeking inside the

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fluxmap. This requires resetting the FluxDecoder, which loses any pending
state, resulting in bad reads for (some) formats which don't have gaps between
sectors --- the DVK MX is the main victim.
This commit is contained in:
David Given
2022-02-12 00:55:09 +01:00
parent 610b7fe95c
commit 0933dc1afa
20 changed files with 204 additions and 227 deletions
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107
arch/ibm/decoder.cc
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@@ -98,58 +98,55 @@ public:
_config(config.ibm())
{}
RecordType advanceToNextRecord() override
nanoseconds_t advanceToNextRecord() override
{
const FluxMatcher* matcher = nullptr;
_sector->clock = _fmr->seekToPattern(ANY_RECORD_PATTERN, matcher);
/* If this is the MFM prefix byte, the the decoder is going to expect three
* extra bytes on the front of the header. */
_currentHeaderLength = (matcher == &MFM_PATTERN) ? 3 : 0;
Fluxmap::Position here = tell();
resetFluxDecoder();
if (_currentHeaderLength > 0)
readRawBits(_currentHeaderLength*16);
auto idbits = readRawBits(16);
const Bytes idbytes = decodeFmMfm(idbits);
uint8_t id = idbytes.slice(0, 1)[0];
if (eof())
return RecordType::UNKNOWN_RECORD;
seek(here);
switch (id)
{
case IBM_IDAM:
return RecordType::SECTOR_RECORD;
case IBM_DAM1:
case IBM_DAM2:
case IBM_TRS80DAM1:
case IBM_TRS80DAM2:
return RecordType::DATA_RECORD;
}
return RecordType::UNKNOWN_RECORD;
return seekToPattern(ANY_RECORD_PATTERN);
}
void decodeSectorRecord() override
{
unsigned recordSize = _currentHeaderLength + IBM_IDAM_LEN;
auto bits = readRawBits(recordSize*16);
auto bytes = decodeFmMfm(bits).slice(0, recordSize);
/* This is really annoying because the IBM record scheme has a
* variable-sized header _and_ the checksum covers this header too. So
* we have to read and decode a byte at a time until we know where the
* record itself starts, saving the bytes for the checksumming later.
*/
Bytes bytes;
ByteWriter bw(bytes);
auto readByte = [&]() {
auto bits = readRawBits(16);
auto bytes = decodeFmMfm(bits).slice(0, 1);
uint8_t byte = bytes[0];
bw.write_8(byte);
return byte;
};
uint8_t id = readByte();
if (id == 0xa1)
{
readByte();
readByte();
id = readByte();
}
if (id != IBM_IDAM)
return;
ByteReader br(bytes);
br.seek(bw.pos);
auto bits = readRawBits(IBM_IDAM_LEN*16);
bw += decodeFmMfm(bits).slice(0, IBM_IDAM_LEN);
IbmDecoderProto::TrackdataProto trackdata;
getTrackFormat(trackdata, _sector->physicalCylinder, _sector->physicalHead);
ByteReader br(bytes);
br.seek(_currentHeaderLength);
br.read_8(); /* skip ID byte */
_sector->logicalTrack = br.read_8();
_sector->logicalSide = br.read_8();
_sector->logicalSector = br.read_8();
_currentSectorSize = 1 << (br.read_8() + 7);
uint16_t gotCrc = crc16(CCITT_POLY, bytes.slice(0, br.pos));
uint16_t wantCrc = br.read_be16();
uint16_t gotCrc = crc16(CCITT_POLY, bytes.slice(0, _currentHeaderLength + 5));
if (wantCrc == gotCrc)
_sector->status = Sector::DATA_MISSING; /* correct but unintuitive */
@@ -163,17 +160,39 @@ public:
void decodeDataRecord() override
{
unsigned recordLength = _currentHeaderLength + _currentSectorSize + 3;
auto bits = readRawBits(recordLength*16);
auto bytes = decodeFmMfm(bits).slice(0, recordLength);
/* This is the same deal as the sector record. */
Bytes bytes;
ByteWriter bw(bytes);
auto readByte = [&]() {
auto bits = readRawBits(16);
auto bytes = decodeFmMfm(bits).slice(0, 1);
uint8_t byte = bytes[0];
bw.write_8(byte);
return byte;
};
uint8_t id = readByte();
if (id == 0xa1)
{
readByte();
readByte();
id = readByte();
}
if ((id != IBM_DAM1) && (id != IBM_DAM2)
&& (id != IBM_TRS80DAM1) && (id != IBM_TRS80DAM2))
return;
ByteReader br(bytes);
br.seek(_currentHeaderLength);
br.read_8(); /* skip ID byte */
br.seek(bw.pos);
auto bits = readRawBits((_currentSectorSize + 2) * 16);
bw += decodeFmMfm(bits).slice(0, _currentSectorSize+2);
_sector->data = br.read(_currentSectorSize);
uint16_t gotCrc = crc16(CCITT_POLY, bytes.slice(0, br.pos));
uint16_t wantCrc = br.read_be16();
uint16_t gotCrc = crc16(CCITT_POLY, bytes.slice(0, recordLength-2));
_sector->status = (wantCrc == gotCrc) ? Sector::OK : Sector::BAD_CHECKSUM;
}