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GimliDS/arm9/source/1541gcr.cpp

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// =====================================================================================
// GimliDS Copyright (c) 2025 Dave Bernazzani (wavemotion-dave)
//
// As GimliDS is a port of the Frodo emulator for the DS/DSi/XL/LL handhelds,
// any copying or distribution of this emulator, its source code and associated
// readme files, with or without modification, are permitted per the original
// Frodo emulator license shown below. Hugest thanks to Christian Bauer for his
// efforts to provide a clean open-source emulation base for the C64.
//
// Numerous hacks and 'unsafe' optimizations have been performed on the original
// Frodo emulator codebase to get it running on the small handheld system. You
// are strongly encouraged to seek out the official Frodo sources if you're at
// all interested in this emulator code.
//
// The GimliDS emulator is offered as-is, without any warranty. Please see readme.md
// =====================================================================================
/*
* 1541gcr.cpp - Emulation of 1541 GCR disk reading/writing
*
* Frodo Copyright (C) Christian Bauer
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Notes:
* ------
*
* - This is only used for processor-level 1541 emulation. It simulates the
* 1541 disk controller hardware (R/W head, GCR reading/writing).
* - The preferences settings for drive 8 are used to specify the disk
* image file.
*
* Incompatibilities:
* ------------------
*
* - No GCR writing implemented (WriteSector is a ROM patch).
* - GCR disk images must be byte-aligned.
* - Programs depending on the exact timing of head movement or doing
* bit rate and motor speed tricks don't work.
*/
#include "sysdeps.h"
#include "1541gcr.h"
#include "CPU1541.h"
#include "IEC.h"
#include "Prefs.h"
// Size of standard GCR sector encoded from D64 image
constexpr unsigned GCR_SECTOR_SIZE = 5 + 10 + 9 + 5 + 325 + 12; // SYNC + Header + Gap + SYNC + Data + Gap
// Duration of disk change sequence step in cycles
constexpr unsigned DISK_CHANGE_SEQ_CYCLES = 500000; // 0.5 s
// Number of sectors of each track
const unsigned num_sectors[41] = {
0,
21,21,21,21,21,21,21,21,21,21,21,21,21,21,21,21,21,
19,19,19,19,19,19,19,
18,18,18,18,18,18,
17,17,17,17,17,
17,17,17,17,17 // Tracks 36..40
};
// Sector offset of start of track in D64 file
const unsigned sector_offset[41] = {
0,
0,21,42,63,84,105,126,147,168,189,210,231,252,273,294,315,336,
357,376,395,414,433,452,471,
490,508,526,544,562,580,
598,615,632,649,666,
683,700,717,734,751 // Tracks 36..40
};
/*
* Constructor: Open image file if processor-level 1541 emulation is enabled
*/
Job1541::Job1541(uint8_t *ram1541) : ram(ram1541), the_file(nullptr)
{
num_tracks = 0;
header_size = 0;
current_halftrack = 0;
gcr_offset = 0;
disk_change_cycle = 0;
disk_change_seq = 0;
cycles_per_byte = 30;
last_byte_cycle = 0;
byte_latch = 0;
motor_on = false;
write_protected = false;
on_sync = false;
byte_ready = false;
for (unsigned i = 0; i < MAX_NUM_HALFTRACKS; ++i) {
gcr_data[i] = nullptr;
gcr_track_length[i] = 0;
}
if (ThePrefs.TrueDrive) {
open_image_file(ThePrefs.DrivePath[0]);
}
}
/*
* Destructor: Close disk image file
*/
Job1541::~Job1541()
{
close_image_file();
}
/*
* Reset GCR emulation
*/
void Job1541::Reset()
{
current_halftrack = 2 * (18 - 1); // Track 18
gcr_offset = 0;
disk_change_seq = 0;
motor_on = false;
on_sync = false;
byte_ready = false;
}
/*
* Preferences may have changed
*/
void Job1541::NewPrefs(const Prefs * prefs)
{
// 1541 emulation turned off?
if (!prefs->TrueDrive) {
close_image_file();
// 1541 emulation turned on?
} else if (!ThePrefs.TrueDrive && prefs->TrueDrive) {
open_image_file(prefs->DrivePath[0]);
// Image file name changed?
}
else if (strcmp(ThePrefs.DrivePath[0], prefs->DrivePath[0]))
{
close_image_file();
open_image_file(prefs->DrivePath[0]);
disk_change_cycle = the_cpu->CycleCounter();
disk_change_seq = 3; // Start disk change WP sensor sequence
the_cpu->Idle = false; // Wake up CPU
}
}
/*
* Check whether file with given header (64 bytes) and size looks like a GCR
* disk image file
*/
bool IsGCRImageFile(const std::string & path, const uint8_t *header, long size)
{
return memcmp(header, "GCR-1541\0", 9) == 0;
}
/*
* Open disk image file
*/
void Job1541::open_image_file(const std::string & filepath)
{
// WP sensor open
write_protected = false;
// Check file type
int type = FILE_IMAGE;
if (type != FILE_IMAGE)
return;
// Try opening the file for reading/writing first, then for reading only
bool read_only = false;
the_file = fopen(filepath.c_str(), "rb+");
if (the_file == nullptr) {
read_only = true;
the_file = fopen(filepath.c_str(), "rb");
}
if (the_file == nullptr)
return;
// Load image file
bool ok = false;
ok = load_image_file();
if (ok) {
// Set write protect status
write_protected = read_only;
} else {
fclose(the_file);
the_file = nullptr;
}
}
/*
* Close disk image file
*/
void Job1541::close_image_file()
{
// Deallocate GCR data
for (unsigned i = 0; i < MAX_NUM_HALFTRACKS; ++i) {
delete[] gcr_data[i];
gcr_data[i] = nullptr;
gcr_track_length[i] = 0;
}
// Close file
if (the_file != nullptr) {
fclose(the_file);
the_file = nullptr;
}
// WP sensor open
write_protected = false;
}
/*
* Load D64/x64 disk image file
*/
bool Job1541::load_image_file()
{
bool has_error_info = false;
// Check length
fseek(the_file, 0, SEEK_END);
size_t size = ftell(the_file);
fseek(the_file, 0, SEEK_SET);
if (size == NUM_SECTORS_35 * 256) {
// 35-track D64
num_tracks = 35;
header_size = 0;
} else if (size == NUM_SECTORS_35 * 257) {
// 35-track D64 with error info
num_tracks = 35;
header_size = 0;
has_error_info = true;
} else if (size == NUM_SECTORS_40 * 256) {
// 40-track D64
num_tracks = 40;
header_size = 0;
} else if (size == NUM_SECTORS_40 * 257) {
// 40-track D64 with error info
num_tracks = 40;
header_size = 0;
has_error_info = true;
} else {
// Check for x64 header
uint8_t header[64];
memset(header, 0, sizeof(header));
fread(header, sizeof(header), 1, the_file);
if (memcmp(header, "C\x15\x41\x64\x01\x02", 6) == 0) {
num_tracks = header[7];
header_size = 64;
if (num_tracks > 40) {
num_tracks = 0;
}
}
}
if (num_tracks == 0) {
return false;
}
// Preset error info (all sectors no error)
memset(error_info, 1, sizeof(error_info));
// Load sector error info from D64 file, if present
if (has_error_info) {
unsigned num_sectors = (num_tracks == 40) ? NUM_SECTORS_40 : NUM_SECTORS_35;
fseek(the_file, num_sectors * 256, SEEK_SET);
fread(&error_info, num_sectors, 1, the_file);
};
// Read BAM and get disk ID
uint8_t bam[256];
read_sector(18, 0, bam);
disk_id1 = bam[162];
disk_id2 = bam[163];
// Create GCR encoded disk data from image
for (unsigned track = 1; track <= num_tracks; ++track) {
// Allocate GCR data
unsigned halftrack = (track - 1) * 2;
gcr_track_length[halftrack] = GCR_SECTOR_SIZE * num_sectors[track];
gcr_data[halftrack] = new uint8_t[gcr_track_length[halftrack]];
// Convert track
for (unsigned sector = 0; sector < num_sectors[track]; ++sector) {
sector2gcr(track, sector, gcr_data[halftrack] + GCR_SECTOR_SIZE * sector);
}
}
return true;
}
/*
* Load G64 disk image file
*/
bool Job1541::load_gcr_file()
{
// Read header
uint8_t header[12];
fread(header, sizeof(header), 1, the_file);
unsigned num_halftracks = header[9];
if (num_halftracks > MAX_NUM_HALFTRACKS)
return false;
num_tracks = num_halftracks / 2;
header_size = 0; // Not relevant for GCR image
// Read track offset table
uint8_t track_offsets[MAX_NUM_HALFTRACKS * 4];
memset(track_offsets, 0, sizeof(track_offsets));
fread(track_offsets, num_halftracks * 4, 1, the_file);
// Read GCR data from file
for (unsigned halftrack = 0; halftrack < num_halftracks; ++halftrack) {
uint32_t offset = ((uint32_t) track_offsets[halftrack * 4 + 0] << 0)
| ((uint32_t) track_offsets[halftrack * 4 + 1] << 8)
| ((uint32_t) track_offsets[halftrack * 4 + 2] << 16)
| ((uint32_t) track_offsets[halftrack * 4 + 3] << 24);
if (offset == 0)
continue;
uint8_t len[2] = { 0, 0 };
fseek(the_file, offset, SEEK_SET);
fread(len, sizeof(len), 1, the_file);
uint16_t length = len[0] | (len[1] << 8);
gcr_track_length[halftrack] = length;
gcr_data[halftrack] = new uint8_t[length];
fread(gcr_data[halftrack], length, 1, the_file);
}
return true;
}
/*
* Write sector to disk (1541 ROM patch)
*/
void Job1541::WriteSector()
{
floppy_soundfx(0); // Play floppy SFX if needed
unsigned track = ram[0x18];
unsigned halftrack = (track - 1) * 2;
unsigned sector = ram[0x19];
uint16_t buf = ram[0x30] | (ram[0x31] << 8);
if (buf <= 0x0700) {
if (write_sector(track, sector, ram + buf)) {
sector2gcr(track, sector, gcr_data[halftrack] + GCR_SECTOR_SIZE * sector);
}
}
}
/*
* Format one track (1541 ROM patch)
*/
void Job1541::FormatTrack()
{
unsigned track = ram[0x51];
unsigned halftrack = (track - 1) * 2;
// Get new ID
uint8_t bufnum = ram[0x3d];
disk_id1 = ram[0x12 + bufnum];
disk_id2 = ram[0x13 + bufnum];
// Create empty block
uint8_t buf[256];
memset(buf, 1, 256);
buf[0] = 0x4b;
// Write block to all sectors on track
for (unsigned sector = 0; sector < num_sectors[track]; ++sector) {
if (write_sector(track, sector, buf)) {
sector2gcr(track, sector, gcr_data[halftrack] + GCR_SECTOR_SIZE * sector);
}
}
// Clear error info (all sectors no error)
if (track == 35) {
memset(error_info, 1, sizeof(error_info));
// Write error_info to disk?
}
}
/*
* Read sector (256 bytes) from image file, return DOS error code (ERR_*)
*/
int Job1541::read_sector(unsigned track, unsigned sector, uint8_t *buffer)
{
if (the_file == nullptr)
return ERR_NOTREADY;
floppy_soundfx(0); // Play floppy SFX if needed
// Convert track/sector to byte offset in file
int offset = offset_from_ts(track, sector);
if (offset < 0)
return ERR_ILLEGALTS;
fseek(the_file, offset + header_size, SEEK_SET);
if (fread(buffer, 1, 256, the_file) != 256) {
return ERR_READ22;
} else {
uint8_t error = error_info[sector_offset[track] + sector];
int get_job_error(int error);
return get_job_error(error);
}
}
/*
* Write sector (256 bytes) to image file
* true: success, false: error
*/
bool Job1541::write_sector(unsigned track, unsigned sector, const uint8_t *buffer)
{
if (the_file == nullptr || write_protected)
return false;
floppy_soundfx(1); // Play floppy SFX if needed
// Convert track/sector to byte offset in image file
int offset = offset_from_ts(track, sector);
if (offset < 0)
return false;
fseek(the_file, offset + header_size, SEEK_SET);
fwrite(buffer, 1, 256, the_file);
return true;
}
/*
* Convert track/sector to offset
*/
int Job1541::offset_from_ts(unsigned track, unsigned sector)
{
if ((track < 1) || (track > num_tracks) ||
(sector < 0) || (sector >= num_sectors[track]))
return -1;
return (sector_offset[track] + sector) << 8;
}
/*
* Convert 4 bytes to 5 GCR encoded bytes
*/
const uint16_t gcr_table[16] = {
0x0a, 0x0b, 0x12, 0x13, 0x0e, 0x0f, 0x16, 0x17,
0x09, 0x19, 0x1a, 0x1b, 0x0d, 0x1d, 0x1e, 0x15
};
void Job1541::gcr_conv4(const uint8_t * from, uint8_t * to)
{
uint16_t g;
g = (gcr_table[*from >> 4] << 5) | gcr_table[*from & 15];
*to++ = g >> 2;
*to = (g << 6) & 0xc0;
from++;
g = (gcr_table[*from >> 4] << 5) | gcr_table[*from & 15];
*to++ |= (g >> 4) & 0x3f;
*to = (g << 4) & 0xf0;
from++;
g = (gcr_table[*from >> 4] << 5) | gcr_table[*from & 15];
*to++ |= (g >> 6) & 0x0f;
*to = (g << 2) & 0xfc;
from++;
g = (gcr_table[*from >> 4] << 5) | gcr_table[*from & 15];
*to++ |= (g >> 8) & 0x03;
*to = g;
}
/*
* Create GCR encoded disk data from image
*/
void Job1541::sector2gcr(unsigned track, unsigned sector, uint8_t * gcr)
{
uint8_t block[256];
uint8_t buf[4];
int error = read_sector(track, sector, block);
uint8_t id1 = disk_id1;
uint8_t id2 = disk_id2;
if (error == ERR_DISKID) { // Disk ID mismatch
id1 ^= 0xff;
id2 ^= 0xff;
}
// Create GCR block header
memset(gcr, 0xff, 5); // SYNC
gcr += 5;
buf[0] = 0x08; // Header mark
buf[1] = sector ^ track ^ id2 ^ id1; // Checksum
buf[2] = sector;
buf[3] = track;
if (error == ERR_READ20) { // Block header not found
buf[0] ^= 0xff;
}
if (error == ERR_READ27) { // Checksum error in header
buf[1] ^= 0xff;
}
gcr_conv4(buf, gcr);
gcr += 5;
buf[0] = id2;
buf[1] = id1;
buf[2] = 0x0f;
buf[3] = 0x0f;
gcr_conv4(buf, gcr);
gcr += 5;
memset(gcr, 0x55, 9); // Gap
gcr += 9;
// Create GCR data block
memset(gcr, 0xff, 5); // SYNC
gcr += 5;
uint8_t sum;
buf[0] = 0x07; // Data mark
sum = buf[1] = block[0];
sum ^= buf[2] = block[1];
sum ^= buf[3] = block[2];
if (error == ERR_READ22) { // Data block not present
buf[0] ^= 0xff;
}
gcr_conv4(buf, gcr);
gcr += 5;
for (unsigned i = 3; i < 255; i += 4) {
sum ^= buf[0] = block[i];
sum ^= buf[1] = block[i+1];
sum ^= buf[2] = block[i+2];
sum ^= buf[3] = block[i+3];
gcr_conv4(buf, gcr);
gcr += 5;
}
sum ^= buf[0] = block[255];
buf[1] = sum; // Checksum
buf[2] = 0;
buf[3] = 0;
if (error == ERR_READ23) { // Checksum error in data block
buf[1] ^= 0xff;
}
gcr_conv4(buf, gcr);
gcr += 5;
memset(gcr, 0x55, 12); // Gap
}
/*
* Set read/write bit rate
*/
void Job1541::SetBitRate(uint8_t rate)
{
static const unsigned cpb[4] = { 32, 30, 28, 26 };
cycles_per_byte = cpb[rate];
}
/*
* Move R/W head out (lower track numbers)
*/
void Job1541::MoveHeadOut()
{
if (!motor_on) // Stepper is inhibited if spindle motor is off
return;
if (current_halftrack == 0)
return;
--current_halftrack;
}
/*
* Move R/W head in (higher track numbers)
*/
void Job1541::MoveHeadIn()
{
if (!motor_on) // Stepper is inhibited if spindle motor is off
return;
if (current_halftrack >= MAX_NUM_HALFTRACKS - 1)
return;
++current_halftrack;
}
/*
* Get state
*/
void Job1541::GetState(Job1541State * s) const
{
s->current_halftrack = current_halftrack;
s->gcr_offset = gcr_offset;
s->cycles_per_byte = cycles_per_byte;
s->last_byte_cycle = last_byte_cycle;
s->disk_change_cycle = disk_change_cycle;
s->byte_latch = byte_latch;
s->disk_change_seq = disk_change_seq;
s->motor_on = motor_on;
s->write_protected = write_protected;
s->on_sync = on_sync;
s->byte_ready = byte_ready;
}
/*
* Set state
*/
void Job1541::SetState(const Job1541State * s)
{
current_halftrack = s->current_halftrack;
gcr_offset = s->gcr_offset;
cycles_per_byte = s->cycles_per_byte;
last_byte_cycle = s->last_byte_cycle;
disk_change_cycle = s->disk_change_cycle;
byte_latch = s->byte_latch;
disk_change_seq = s->disk_change_seq;
motor_on = s->motor_on;
write_protected = s->write_protected;
on_sync = s->on_sync;
byte_ready = s->byte_ready;
}
/*
* Advance disk change sequence state
*/
void Job1541::advance_disk_change_seq(uint32_t cycle_counter)
{
if (disk_change_seq > 0) {
// Time for next step in sequence?
uint32_t elapsed = cycle_counter - disk_change_cycle;
if (elapsed >= DISK_CHANGE_SEQ_CYCLES) {
--disk_change_seq;
disk_change_cycle = cycle_counter;
}
}
}
/*
* Rotate disk (virtually)
*/
void Job1541::rotate_disk(uint32_t cycle_counter)
{
advance_disk_change_seq(cycle_counter);
if (motor_on && disk_change_seq == 0 && gcr_data[current_halftrack] != nullptr) {
uint32_t elapsed = cycle_counter - last_byte_cycle;
uint32_t advance = elapsed / cycles_per_byte;
if (advance > 0) {
size_t track_length = gcr_track_length[current_halftrack];
gcr_offset += advance;
while (gcr_offset >= track_length) {
gcr_offset -= track_length;
}
const uint8_t * p = gcr_data[current_halftrack] + gcr_offset;
// Sync = ten "1" bits
if (gcr_offset != 0) {
on_sync = ((p[-1] & 0x03) == 0x03) && (p[0] == 0xff);
} else {
on_sync = ((gcr_data[current_halftrack][track_length - 1] & 0x03) == 0x03) && (p[0] == 0xff);
}
// Byte is ready if not on sync
if (! on_sync) {
if (! byte_ready) {
byte_latch = p[0];
byte_ready = true;
}
} else {
byte_ready = false;
}
last_byte_cycle += advance * cycles_per_byte;
}
} else {
last_byte_cycle = cycle_counter;
on_sync = false;
byte_ready = false;
}
}
/*
* Check if R/W head is over SYNC
*/
bool Job1541::SyncFound(uint32_t cycle_counter)
{
rotate_disk(cycle_counter);
return on_sync;
}
/*
* Check if GCR byte is available for reading
*/
bool Job1541::ByteReady(uint32_t cycle_counter)
{
rotate_disk(cycle_counter);
return byte_ready;
}
/*
* Read one GCR byte from disk
*/
uint8_t Job1541::ReadGCRByte(uint32_t cycle_counter)
{
floppy_soundfx(0); // Play floppy SFX if needed
rotate_disk(cycle_counter);
byte_ready = false;
return byte_latch;
}
/*
* Return state of write protect sensor
*/
bool Job1541::WPSensorClosed(uint32_t cycle_counter)
{
advance_disk_change_seq(cycle_counter);
#if 0 //TODO: figure out why this isn't working...
if (disk_change_seq == 3 || disk_change_seq == 1) {
return true;
} else if (disk_change_seq == 2) {
return false;
}
#endif
// Default behavior
return write_protected;
}
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