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Add Micropolis decoder

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Resolves #187
This commit is contained in:
Eric Anderson
2020-10-03 13:05:06 -05:00
parent 3b02bc8cf1
commit 82bd1bead4
6 changed files with 153 additions and 0 deletions
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56
arch/micropolis/decoder.cc Normal file
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#include "globals.h"
#include "fluxmap.h"
#include "decoders/fluxmapreader.h"
#include "decoders/decoders.h"
#include "sector.h"
#include "micropolis.h"
#include "bytes.h"
#include "fmt/format.h"
/* The sector has a preamble of MFM 0x00s and uses 0xFF as a sync pattern. */
static const FluxPattern SECTOR_SYNC_PATTERN(32, 0xaaaa5555);
AbstractDecoder::RecordType MicropolisDecoder::advanceToNextRecord()
{
_fmr->seekToIndexMark();
const FluxMatcher* matcher = nullptr;
_sector->clock = _fmr->seekToPattern(SECTOR_SYNC_PATTERN, matcher);
if (matcher == &SECTOR_SYNC_PATTERN) {
readRawBits(16);
return SECTOR_RECORD;
}
return UNKNOWN_RECORD;
}
static uint8_t checksum(const Bytes& bytes) {
ByteReader br(bytes);
uint16_t sum = 0;
while (!br.eof()) {
sum += br.read_8();
}
return (sum & 0xFF) + (sum >> 8);
}
void MicropolisDecoder::decodeSectorRecord()
{
auto rawbits = readRawBits(MICROPOLIS_ENCODED_SECTOR_SIZE*16);
auto bytes = decodeFmMfm(rawbits).slice(0, MICROPOLIS_ENCODED_SECTOR_SIZE);
ByteReader br(bytes);
br.read_8(); /* sync */
_sector->logicalTrack = br.read_8();
_sector->logicalSide = _sector->physicalSide;
_sector->logicalSector = br.read_8();
if (_sector->logicalSector > 15)
return;
if (_sector->logicalTrack > 77)
return;
br.read(10); /* OS data or padding */
_sector->data = br.read(256);
uint8_t wantChecksum = br.read_8();
uint8_t gotChecksum = checksum(bytes.slice(1, 2+266));
br.read(5); /* 4 byte ECC and ECC-present flag */
_sector->status = (wantChecksum == gotChecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
}