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Archival checking: IBM FM works (but not MFM yet). Other formats have stopped

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working.
This commit is contained in:
David Given
2019-04-26 23:52:04 +02:00
parent 643288bef8
commit a483ad987e
6 changed files with 190 additions and 20 deletions
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153
lib/ibm/decoder.cc
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@@ -3,6 +3,7 @@
#include "ibm.h"
#include "crc.h"
#include "fluxmap.h"
#include "fluxmapreader.h"
#include "sector.h"
#include "record.h"
#include <string.h>
@@ -10,6 +11,153 @@
static_assert(std::is_trivially_copyable<IbmIdam>::value,
"IbmIdam is not trivially copyable");
/*
* The markers at the beginning of records are special, and have
* missing clock pulses, allowing them to be found by the logic.
*
* IAM record:
* flux: XXXX-XXX-XXXX-X- = 0xf77a
* clock: X X - X - X X X = 0xd7
* data: X X X X X X - - = 0xfc
*
* (We just ignore this one --- it's useless and optional.)
*/
/*
* IDAM record:
* flux: XXXX-X-X-XXXXXX- = 0xf57e
* clock: X X - - - X X X = 0xc7
* data: X X X X X X X - = 0xfe
*/
const FluxPattern FM_IDAM_PATTERN(16, 0xf57e);
/*
* DAM1 record:
* flux: XXXX-X-X-XX-X-X- = 0xf56a
* clock: X X - - - X X X = 0xc7
* data: X X X X X - - - = 0xf8
*/
const FluxPattern FM_DAM1_PATTERN(16, 0xf56a);
/*
* DAM2 record:
* flux: XXXX-X-X-XX-XXXX = 0xf56f
* clock: X X - - - X X X = 0xc7
* data: X X X X X - X X = 0xfb
*/
const FluxPattern FM_DAM2_PATTERN(16, 0xf56f);
/*
* TRS80DAM1 record:
* flux: XXXX-X-X-XX-X-XX = 0xf56b
* clock: X X - - - X X X = 0xc7
* data: X X X X X - - X = 0xf9
*/
const FluxPattern FM_TRS80DAM1_PATTERN(16, 0xf56b);
/*
* TRS80DAM2 record:
* flux: XXXX-X-X-XX-XXX- = 0xf56c
* clock: X X - - - X X X = 0xc7
* data: X X X X X - X - = 0xfa
*/
const FluxPattern FM_TRS80DAM2_PATTERN(16, 0xf56c);
/* MFM record separator:
* 0xA1 is:
* data: 1 0 1 0 0 0 0 1 = 0xa1
* mfm: 01 00 01 00 10 10 10 01 = 0x44a9
* special: 01 00 01 00 10 00 10 01 = 0x4489
* ^^^^^
* When shifted out of phase, the special 0xa1 byte becomes an illegal
* encoding (you can't do 10 00). So this can't be spoofed by user data.
*
* shifted: 10 00 10 01 00 01 00 1
*/
const FluxPattern MFM_PATTERN(16, 0x4489);
const FluxMatchers SEPARATOR_PATTERNS(
{
&MFM_PATTERN,
&FM_IDAM_PATTERN,
// &FM_DAM1_PATTERN,
&FM_DAM2_PATTERN,
// &FM_TRS80DAM1_PATTERN,
// &FM_TRS80DAM2_PATTERN,
}
);
nanoseconds_t IbmDecoder::findSector(FluxmapReader& fmr, Track& track)
{
for (;;)
{
nanoseconds_t clock = fmr.seekToPattern(SEPARATOR_PATTERNS);
if (fmr.eof() || !clock)
return 0;
auto here = fmr.tell();
auto idbits = fmr.readRawBits(16, clock);
uint8_t id = decodeFmMfm(idbits).slice(0, 1)[0];
fmr.seek(here);
/* Check for the MFM prefix, and skip it. */
if (id == IBM_MFM_SYNC)
fmr.readRawBits(48, clock);
switch (id)
{
case IBM_IDAM:
case IBM_DAM1:
case IBM_DAM2:
case IBM_TRS80DAM1:
case IBM_TRS80DAM2:
return clock;
}
fmr.readRawBit(clock);
}
}
nanoseconds_t IbmDecoder::findData(FluxmapReader& fmr, Track& track)
{
return findSector(fmr, track);
}
void IbmDecoder::decodeHeader(FluxmapReader& fmr, Track& track, Sector& sector)
{
auto bits = fmr.readRawBits(IBM_IDAM_LEN*16, sector.clock);
auto bytes = decodeFmMfm(bits).slice(0, IBM_IDAM_LEN);
ByteReader br(bytes);
uint8_t id = br.read_8();
if (id != IBM_IDAM)
return;
sector.logicalTrack = br.read_8();
sector.logicalSide = br.read_8();
sector.logicalSector = br.read_8() - _sectorBase;
_sectorSize = 1 << (br.read_8() + 7);
uint16_t wantCrc = br.read_be16();
uint16_t gotCrc = crc16(CCITT_POLY, bytes.slice(0, 5));
if (wantCrc == gotCrc)
sector.status = Sector::DATA_MISSING; /* correct but unintuitive */
}
void IbmDecoder::decodeData(FluxmapReader& fmr, Track& track, Sector& sector)
{
unsigned recordLength = _sectorSize + 3;
auto bits = fmr.readRawBits(recordLength*16, sector.clock);
auto bytes = decodeFmMfm(bits).slice(0, recordLength);
ByteReader br(bytes);
uint8_t id = br.read_8();
if ((id != IBM_DAM1) && (id != IBM_DAM2) && (id != IBM_TRS80DAM1) && (id != IBM_TRS80DAM2))
return;
sector.data = br.read(_sectorSize);
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;
}
#if 0
SectorVector AbstractIbmDecoder::decodeToSectors(const RawRecordVector& rawRecords, unsigned, unsigned)
{
bool idamValid = false;
@@ -140,7 +288,7 @@ int IbmMfmDecoder::recordMatcher(uint64_t fifo) const
* can't be bothered.
*
* 0xC2 is:
* data: 1 1 0 0 0 0 1 0
* data: 1 1 0 0 0 0 1 0 = 0xc2
* mfm: 01 01 00 10 10 10 01 00 = 0x5254
* special: 01 01 00 10 00 10 01 00 = 0x5224
* ^^^^
@@ -152,7 +300,7 @@ int IbmMfmDecoder::recordMatcher(uint64_t fifo) const
* All other records use 0xA1 as a marker:
*
* 0xA1 is:
* data: 1 0 1 0 0 0 0 1
* data: 1 0 1 0 0 0 0 1 = 0xa1
* mfm: 01 00 01 00 10 10 10 01 = 0x44A9
* special: 01 00 01 00 10 00 10 01 = 0x4489
* ^^^^^
@@ -168,3 +316,4 @@ int IbmMfmDecoder::recordMatcher(uint64_t fifo) const
return 48;
return 0;
}
#endif