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fluxengine/arch/c64/encoder.cc
David Given 15a69f6dcb Make build with the new ab --- but the tests fail.
2025-03-17 22:33:54 +01:00

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#include "lib/core/globals.h"
#include "lib/core/utils.h"
#include "lib/decoders/decoders.h"
#include "lib/encoders/encoders.h"
#include "arch/c64/c64.h"
#include "lib/core/crc.h"
#include "lib/data/sector.h"
#include "lib/data/image.h"
#include "fmt/format.h"
#include "arch/c64/c64.pb.h"
#include "lib/encoders/encoders.pb.h"
#include "lib/data/layout.h"
#include <ctype.h>
#include "lib/core/bytes.h"
static bool lastBit;
static int encode_data_gcr(uint8_t data)
{
switch (data)
{
#define GCR_ENTRY(gcr, data) \
case data: \
return gcr;
#include "data_gcr.h"
#undef GCR_ENTRY
}
return -1;
}
static void write_bits(
std::vector<bool>& bits, unsigned& cursor, const std::vector<bool>& src)
{
for (bool bit : src) // Range-based for loop
{
if (cursor < bits.size())
bits[cursor++] = bit;
}
}
static void write_bits(
std::vector<bool>& bits, unsigned& cursor, uint64_t data, int width)
{
cursor += width;
for (int i = 0; i < width; i++)
{
unsigned pos = cursor - i - 1;
if (pos < bits.size())
bits[pos] = data & 1;
data >>= 1;
}
}
static std::vector<bool> encode_data(uint8_t input)
{
/*
* Four 8-bit data bytes are converted to four 10-bit GCR bytes at a time by
* the 1541 DOS. RAM is only an 8-bit storage device though. This hardware
* limitation prevents a 10-bit GCR byte from being stored in a single
* memory location. Four 10-bit GCR bytes total 40 bits - a number evenly
* divisible by our overriding 8-bit constraint. Commodore sub- divides the
* 40 GCR bits into five 8-bit bytes to solve this dilemma. This explains
* why four 8-bit data bytes are converted to GCR form at a time. The
* following step by step example demonstrates how this bit manipulation is
* performed by the DOS.
*
* STEP 1. Four 8-bit Data Bytes
* $08 $10 $00 $12
*
* STEP 2. Hexadecimal to Binary Conversion
* 1. Binary Equivalents
* $08 $10 $00 $12
* 00001000 00010000 00000000 00010010
*
* STEP 3. Binary to GCR Conversion
* 1. Four 8-bit Data Bytes
* 00001000 00010000 00000000 00010010
* 2. High and Low Nybbles
* 0000 1000 0001 0000 0000 0000 0001 0010
* 3. High and Low Nybble GCR Equivalents
* 01010 01001 01011 01010 01010 01010 01011 10010
* 4. Four 10-bit GCR Bytes
* 0101001001 0101101010 0101001010 0101110010
*
* STEP 4. 10-bit GCR to 8-bit GCR Conversion
* 1. Concatenate Four 10-bit GCR Bytes
* 0101001001010110101001010010100101110010
* 2. Five 8-bit Subdivisions
* 01010010 01010110 10100101 00101001 01110010
*
* STEP 5. Binary to Hexadecimal Conversion
* 1. Hexadecimal Equivalents
* 01010010 01010110 10100101 00101001 01110010
* $52 $56 $A5 $29 $72
*
* STEP 6. Four 8-bit Data Bytes are Recorded as Five 8-bit GCR Bytes
* $08 $10 $00 $12
*
* are recorded as
* $52 $56 $A5 $29 $72
*/
std::vector<bool> output(10, false);
uint8_t hi = 0;
uint8_t lo = 0;
uint8_t lo_GCR = 0;
uint8_t hi_GCR = 0;
// Convert the byte in high and low nibble
lo = input >> 4; // get the lo nibble shift the bits 4 to the right
hi = input & 15; // get the hi nibble bij masking the lo bits (00001111)
lo_GCR = encode_data_gcr(lo); // example value: 0000 GCR = 01010
hi_GCR = encode_data_gcr(hi); // example value: 1000 GCR = 01001
// output = [0,1,2,3,4,5,6,7,8,9]
// value = [0,1,0,1,0,0,1,0,0,1]
// 01010 01001
int b = 4;
for (int i = 0; i < 10; i++)
{
if (i < 5) // 01234
{ // i = 0 op
output[4 - i] = (lo_GCR & 1); // 01010
// 01010 -> & 00001 -> 00000 output[4] = 0
// 00101 -> & 00001 -> 00001 output[3] = 1
// 00010 -> & 00001 -> 00000 output[2] = 0
// 00001 -> & 00001 -> 00001 output[1] = 1
// 00000 -> & 00001 -> 00000 output[0] = 0
lo_GCR >>= 1;
}
else
{
output[i + b] = (hi_GCR & 1); // 01001
// 01001 -> & 00001 -> 00001 output[9] = 1
// 00100 -> & 00001 -> 00000 output[8] = 0
// 00010 -> & 00001 -> 00000 output[7] = 0
// 00001 -> & 00001 -> 00001 output[6] = 1
// 00000 -> & 00001 -> 00000 output[5] = 0
hi_GCR >>= 1;
b = b - 2;
}
}
return output;
}
class Commodore64Encoder : public Encoder
{
public:
Commodore64Encoder(const EncoderProto& config):
Encoder(config),
_config(config.c64())
{
}
public:
std::unique_ptr<Fluxmap> encode(std::shared_ptr<const TrackInfo>& trackInfo,
const std::vector<std::shared_ptr<const Sector>>& sectors,
const Image& image) override
{
/* The format ID Character # 1 and # 2 are in the .d64 image only
* present in track 18 sector zero which contains the BAM info in byte
* 162 and 163. it is written in every header of every sector and track.
* headers are not stored in a d64 disk image so we have to get it from
* track 18 which contains the BAM.
*/
const auto& sectorData = image.get(
C64_BAM_TRACK, 0, 0); // Read de BAM to get the DISK ID bytes
if (sectorData)
{
ByteReader br(sectorData->data);
br.seek(162); // goto position of the first Disk ID Byte
_formatByte1 = br.read_8();
_formatByte2 = br.read_8();
}
else
_formatByte1 = _formatByte2 = 0;
double clockRateUs = clockPeriodForC64Track(trackInfo->logicalTrack);
int bitsPerRevolution = 200000.0 / clockRateUs;
std::vector<bool> bits(bitsPerRevolution);
unsigned cursor = 0;
fillBitmapTo(bits,
cursor,
_config.post_index_gap_us() / clockRateUs,
{true, false});
lastBit = false;
for (const auto& sector : sectors)
writeSector(bits, cursor, sector);
if (cursor >= bits.size())
error("track data overrun by {} bits", cursor - bits.size());
fillBitmapTo(bits, cursor, bits.size(), {true, false});
std::unique_ptr<Fluxmap> fluxmap(new Fluxmap);
fluxmap->appendBits(
bits, calculatePhysicalClockPeriod(clockRateUs * 1e3, 200e6));
return fluxmap;
}
private:
void writeSector(std::vector<bool>& bits,
unsigned& cursor,
std::shared_ptr<const Sector> sector) const
{
/* Source: http://www.unusedino.de/ec64/technical/formats/g64.html
* 1. Header sync FF FF FF FF FF (40 'on' bits, not GCR)
* 2. Header info 52 54 B5 29 4B 7A 5E 95 55 55 (10 GCR bytes)
* 3. Header gap 55 55 55 55 55 55 55 55 55 (9 bytes, never read)
* 4. Data sync FF FF FF FF FF (40 'on' bits, not GCR)
* 5. Data block 55...4A (325 GCR bytes)
* 6. Inter-sector gap 55 55 55 55...55 55 (4 to 12 bytes, never read)
* 1. Header sync (SYNC for the next sector)
*/
if ((sector->status == Sector::OK) or
(sector->status == Sector::BAD_CHECKSUM))
{
// There is data to encode to disk.
if ((sector->data.size() != C64_SECTOR_LENGTH))
error("unsupported sector size {} --- you must pick 256",
sector->data.size());
// 1. Write header Sync (not GCR)
for (int i = 0; i < 6; i++)
write_bits(
bits, cursor, C64_HEADER_DATA_SYNC, 1 * 8); /* sync */
// 2. Write Header info 10 GCR bytes
/*
* The 10 byte header info (#2) is GCR encoded and must be decoded
* to it's normal 8 bytes to be understood. Once decoded, its
* breakdown is as follows:
*
* Byte $00 - header block ID ($08)
* 01 - header block checksum 16 (EOR of $02-$05)
* 02 - Sector
* 03 - Track
* 04 - Format ID byte #2
* 05 - Format ID byte #1
* 06-07 - $0F ("off" bytes)
*/
uint8_t encodedTrack =
((sector->logicalTrack) +
1); // C64 track numbering starts with 1. Fluxengine with 0.
uint8_t encodedSector = sector->logicalSector;
// uint8_t formatByte1 = C64_FORMAT_ID_BYTE1;
// uint8_t formatByte2 = C64_FORMAT_ID_BYTE2;
uint8_t headerChecksum =
(encodedTrack ^ encodedSector ^ _formatByte1 ^ _formatByte2);
write_bits(bits, cursor, encode_data(C64_HEADER_BLOCK_ID));
write_bits(bits, cursor, encode_data(headerChecksum));
write_bits(bits, cursor, encode_data(encodedSector));
write_bits(bits, cursor, encode_data(encodedTrack));
write_bits(bits, cursor, encode_data(_formatByte2));
write_bits(bits, cursor, encode_data(_formatByte1));
write_bits(bits, cursor, encode_data(C64_PADDING));
write_bits(bits, cursor, encode_data(C64_PADDING));
// 3. Write header GAP not GCR
for (int i = 0; i < 9; i++)
write_bits(
bits, cursor, C64_HEADER_GAP, 1 * 8); /* header gap */
// 4. Write Data sync not GCR
for (int i = 0; i < 6; i++)
write_bits(
bits, cursor, C64_HEADER_DATA_SYNC, 1 * 8); /* sync */
// 5. Write data block 325 GCR bytes
/*
* The 325 byte data block (#5) is GCR encoded and must be decoded
* to its normal 260 bytes to be understood. The data block is made
* up of the following:
*
* Byte $00 - data block ID ($07)
* 01-100 - 256 bytes data
* 101 - data block checksum (EOR of $01-100)
* 102-103 - $00 ("off" bytes, to make the sector size a
* multiple of 5)
*/
write_bits(bits, cursor, encode_data(C64_DATA_BLOCK_ID));
uint8_t dataChecksum = xorBytes(sector->data);
ByteReader br(sector->data);
int i = 0;
for (i = 0; i < C64_SECTOR_LENGTH; i++)
{
uint8_t val = br.read_8();
write_bits(bits, cursor, encode_data(val));
}
write_bits(bits, cursor, encode_data(dataChecksum));
write_bits(bits, cursor, encode_data(C64_PADDING));
write_bits(bits, cursor, encode_data(C64_PADDING));
// 6. Write inter-sector gap 9 - 12 bytes nor gcr
for (int i = 0; i < 9; i++)
write_bits(
bits, cursor, C64_INTER_SECTOR_GAP, 1 * 8); /* sync */
}
}
private:
const Commodore64EncoderProto& _config;
uint8_t _formatByte1;
uint8_t _formatByte2;
};
std::unique_ptr<Encoder> createCommodore64Encoder(const EncoderProto& config)
{
return std::unique_ptr<Encoder>(new Commodore64Encoder(config));
}
// vim: sw=4 ts=4 et
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