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Make the DS990 decoder work.

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This commit is contained in:
David Given
2020-08-21 00:32:36 +02:00
parent c375c948c0
commit 03dd689f17
3 changed files with 71 additions and 45 deletions
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105
arch/tids990/decoder.cc
View File

@@ -8,54 +8,79 @@
#include "record.h"
#include "track.h"
#include <string.h>
#include <fmt/format.h>
const int SECTOR_SIZE = 256;
/* The Texas Instruments DS990 uses MFM with a scheme similar to a simplified
* version of the IBM record scheme (it's actually easier to parse than IBM).
* There are 26 sectors per track, each holding a rather weird 288 bytes.
*/
const FluxPattern ID_PATTERN(32, 0xaaaaffaf);
/*
* Sector record:
* data: 0 1 0 1 0 1 0 1 .0 0 0 0 1 0 1 0 = 0x550a
* mfm: 00 01 00 01 00 01 00 01.00 10 10 10 01 00 01 00 = 0x11112a44
* special: 00 01 00 01 00 01 00 01.00 10 00 10 01 00 01 00 = 0x11112244
* ^^
* 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.
*/
const FluxPattern SECTOR_RECORD_PATTERN(32, 0x11112244);
/*
* Data record:
* data: 0 1 0 1 0 1 0 1 .0 0 0 0 1 0 1 1 = 0x550c
* mfm: 00 01 00 01 00 01 00 01.00 10 10 10 01 00 01 01 = 0x11112a45
* special: 00 01 00 01 00 01 00 01.00 10 00 10 01 00 01 01 = 0x11112245
* ^^
* 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.
*/
const FluxPattern DATA_RECORD_PATTERN(32, 0x11112245);
const FluxMatchers ANY_RECORD_PATTERN({ &SECTOR_RECORD_PATTERN, &DATA_RECORD_PATTERN });
AbstractDecoder::RecordType TiDs990Decoder::advanceToNextRecord()
{
return UNKNOWN_RECORD;
// if (_currentSector == -1)
// {
// /* First sector in the track: look for the sync marker. */
// const FluxMatcher* matcher = nullptr;
// _sector->clock = _clock = _fmr->seekToPattern(ID_PATTERN, matcher);
// readRawBits(32); /* skip the ID mark */
// _logicalTrack = decodeFmMfm(readRawBits(32)).slice(0, 32).reader().read_be16();
// }
// else if (_currentSector == 10)
// {
// /* That was the last sector on the disk. */
// return UNKNOWN_RECORD;
// }
// else
// {
// /* Otherwise we assume the clock from the first sector is still valid.
// * The decoder framwork will automatically stop when we hit the end of
// * the track. */
// _sector->clock = _clock;
// }
//
// _currentSector++;
// return SECTOR_RECORD;
const FluxMatcher* matcher = nullptr;
_sector->clock = _fmr->seekToPattern(ANY_RECORD_PATTERN, matcher);
if (matcher == &SECTOR_RECORD_PATTERN)
return RecordType::SECTOR_RECORD;
if (matcher == &DATA_RECORD_PATTERN)
return RecordType::DATA_RECORD;
return RecordType::UNKNOWN_RECORD;
}
void TiDs990Decoder::decodeSectorRecord()
{
// auto bits = readRawBits((SECTOR_SIZE+2)*16);
// auto bytes = decodeFmMfm(bits).slice(0, SECTOR_SIZE+2).swab();
//
// uint16_t gotChecksum = 0;
// ByteReader br(bytes);
// for (int i=0; i<(SECTOR_SIZE/2); i++)
// gotChecksum += br.read_le16();
// uint16_t wantChecksum = br.read_le16();
//
// _sector->logicalTrack = _logicalTrack;
// _sector->logicalSide = _track->physicalSide;
// _sector->logicalSector = _currentSector;
// _sector->data = bytes.slice(0, SECTOR_SIZE);
// _sector->status = (gotChecksum == wantChecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
auto bits = readRawBits(TIDS990_SECTOR_RECORD_SIZE*16);
auto bytes = decodeFmMfm(bits).slice(0, TIDS990_SECTOR_RECORD_SIZE);
ByteReader br(bytes);
uint16_t gotChecksum = crc16(CCITT_POLY, bytes.slice(1, TIDS990_SECTOR_RECORD_SIZE-3));
br.seek(2);
_sector->logicalSide = br.read_8() >> 3;
_sector->logicalTrack = br.read_8();
br.read_8(); /* number of sectors per track */
_sector->logicalSector = br.read_8();
br.read_be16(); /* sector size */
uint16_t wantChecksum = br.read_be16();
if (wantChecksum == gotChecksum)
_sector->status = Sector::DATA_MISSING; /* correct but unintuitive */
}
void TiDs990Decoder::decodeDataRecord()
{
auto bits = readRawBits(TIDS990_DATA_RECORD_SIZE*16);
auto bytes = decodeFmMfm(bits).slice(0, TIDS990_DATA_RECORD_SIZE);
ByteReader br(bytes);
uint16_t gotChecksum = crc16(CCITT_POLY, bytes.slice(1, TIDS990_DATA_RECORD_SIZE-3));
br.seek(2);
_sector->data = br.read(TIDS990_PAYLOAD_SIZE);
uint16_t wantChecksum = br.read_be16();
_sector->status = (wantChecksum == gotChecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
}

7
arch/tids990/tids990.h
View File

@@ -1,9 +1,9 @@
#ifndef TIDS990_H
#define TIDS990_H
#define TIDS990_RECORD_SIZE 0x516 /* bytes */
#define TIDS990_ID_SIZE 17
#define TIDS990_PAYLOAD_SIZE 0x500
#define TIDS990_PAYLOAD_SIZE 288 /* bytes */
#define TIDS990_SECTOR_RECORD_SIZE 10 /* bytes */
#define TIDS990_DATA_RECORD_SIZE (TIDS990_PAYLOAD_SIZE + 4) /* bytes */
class Sector;
class Fluxmap;
@@ -16,6 +16,7 @@ public:
RecordType advanceToNextRecord();
void decodeSectorRecord();
void decodeDataRecord();
};
#endif

4
src/fe-readtids990.cc
View File

@@ -13,8 +13,8 @@ static FlagGroup flags { &readerFlags };
int mainReadTiDs990(int argc, const char* argv[])
{
setReaderDefaultSource(":t=0-79:s=0");
setReaderDefaultOutput("dfs.img");
setReaderDefaultSource(":t=0-76");
setReaderDefaultOutput("tids990.img");
setReaderRevolutions(2);
flags.parseFlags(argc, argv);