disk.cpp

#include <unistd.h>
#include <stdint.h>
#include <pgmspace.h>

#include <machine.h>
#include <memory.h>
#include <CPU.h>
#include <prom.h>
#include <debugging.h>
#include <serialio.h>
#include <filer.h>
#include <flash_filer.h>

#include "config.h"
#include "softswitches.h"
#include "disk.h"

// geometry
#define BYTES_PER_SECTOR	256
#define SECTORS_PER_TRACK	16
#define MAX_TRACK	35

#define CMD_SEEK	0
#define CMD_READ	1
#define CMD_WRITE	2
#define CMD_FORMAT	4

#define NO_ERROR	0x00
#define WRITE_PROTECT	0x10
#define VOLUME_ERROR	0x20
#define DRIVE_ERROR	0x40
#define READ_ERROR	0x80

// see https://gswv.apple2.org.za/a2zine/GS.WorldView/Resources/DOS.3.3.ANATOMY/BOOT.PROCESS.txt
// https://htmlpreview.github.io/?https://github.com/Michaelangel007/apple2_dos33/blob/master/dos33.html

// zpage locations
#define TRACK	0x41
#define SECTOR	0x3d
#define DATAPTR	0x26
#define IOBP	0x48
#define SLOTIDX	0x2b

// the disk is accessed for the first time with PR #6 "permanent redirect to slot #6"
static const uint8_t diskboot[] PROGMEM = {

	// .org $c600
	// https://6502disassembly.com/a2-rom/C600ROM.html
	0xa2, 0x20,		// ldx #$20
	0xa0, 0x00,		// ldy #$00
	0xa2, 0x03,		// ldx #$03
				// CreateDecTabLoop
	0x86, 0x3c,		// stx bits
	0x8a,			// txa
	0x0a,			// asl A
	0x24, 0x3c,		// bit bits
	0xf0, 0x10,		// beq :reject
	0x05, 0x3c,		// ora bits
	0x49, 0xff,		// eor #$ff
	0x29, 0x7e,		// and #$7e
				// :check_dub0
	0xb0, 0x08,		// bcs :reject
	0x4a,			// lsr A
	0xd0, 0xfb,		// bne :check_dub0
	0x98,			// tya
	0x9d, 0x56, 0x03,	// sta CONV_TAB,x
	0xc8,			// iny
				// :reject
	0xe8,			// inx
	0x10, 0xe5,		// bpl CreateDecTabLoop
	0x20, 0x58, 0xff,	// jsr MON_IORTS
	0xba,			// tsx
	0xbd, 0x00, 0x01,	// lda STACK,x
	0x0a,			// asl A
	0x0a,			// asl A
	0x0a,			// asl A
	0x0a,			// asl A
	0x85, SLOTIDX,		// sta slot_index
	0xaa,			// tax
	// replaced with NOPs (to avoid hitting soft-switches)
	0xea, 0xea, 0xea,	// lda IWM_Q7_OFF,x
	0xea, 0xea, 0xea,	// lda IWM_Q6_OFF,x
	0xea, 0xea, 0xea,	// lda IWM_SEL_DRIVE_1,x
	0xea, 0xea, 0xea,	// lda IWM_MOTOR_ON,x
				// "Blind-seek to track 0."
	0xea, 0xea,		// replaced with NOPs
				// :seek_loop
	0xea, 0xea, 0xea,
	0xea,
	0xea, 0xea,
	0xea,
	0xea, 0xea,
	0xea,
	0xea, 0xea, 0xea,
	0xea, 0xea,
	0xea, 0xea, 0xea,
	0xea,
	0xa9, 0x00,		// lda #$00 (was bpl :seek_loop)
	0x85, DATAPTR,		// sta data_ptr
	0x85, SECTOR,		// sta sector
	0x85, TRACK,		// sta track
	0xa9, 0x08,		// lda #>BOOT1
	0x85, DATAPTR+1,	// sta data_ptr+1

	// .org $c65c ReadSector (don't change: this is called from BOOT1)
				// :another
	0xbd, 0x80, 0xc0,	// lda $c080,x
	0xd0, 0x10,		// bne :abort
	0xe6, DATAPTR+1,	// inc data_ptr+1
	0xe6, SECTOR,		// inc sector
	0xa5, SECTOR,		// lda sector
	0xcd, 0x00, 0x08,	// cmp BOOT1
	0xa6, SLOTIDX,		// ldx slot_index
	0x90, 0xf3,		// bcc :another
	0x4c, 0x01, 0x08,	// jmp BOOT1+1
				// :abort
	0x4c, 0x00, 0xe0,	// jmp $e000
};

DiskII::DiskII(Memory &memory, flash_file &drive1, flash_file &drive2):
	bootprom(diskboot, sizeof(diskboot)), _memory(memory)
{
	_drives[0] = &drive1;
	_drives[1] = &drive2;
}

void DiskII::seek(flash_file *drive, uint8_t trk, uint8_t sec) {

	drive->seek(BYTES_PER_SECTOR * (sec + trk * SECTORS_PER_TRACK));
}

uint16_t DiskII::read(flash_file *drive, Memory::address addr, uint16_t bytes) {

	uint16_t i;
	for (i = 0; i < bytes && drive->more(); i++)
		_memory[addr++] = drive->read();
	return i;
}

uint16_t DiskII::write(flash_file *drive, Memory::address addr, uint16_t bytes) {

	uint16_t i;
	for (i = 0; i < bytes; i++)
		drive->write(_memory[addr++]);
	return i;
}

static const uint8_t reverse_sector_map[] = {
	0, 7, 14, 6, 13, 5, 12, 4,
	11, 3, 10, 2, 9, 1, 8, 15
};

uint8_t DiskII::boot1() {

	uint8_t sector = reverse_sector_map[_memory[SECTOR]];
	uint8_t track = _memory[TRACK];
	Memory::address data_ptr = _memory[DATAPTR] | (_memory[DATAPTR+1] << 8);

	DBG_DISK("boot1: (%d) %02x %02x %04x", _boot, track, sector, data_ptr);
	flash_file *drive = _drives[0];
	if (!*drive)
		return 0x01;

	seek(drive, track, sector);
	read(drive, data_ptr, BYTES_PER_SECTOR);
	_boot++;

	if (_boot == 11) {
		// now we've read the first sector (BOOT0) _and_
		// the first 10 sectors (BOOT1). from now on
		// DOS will call RWTS (at $3d00), so patch that.
		//
		// RWTS begins with this, so keep it:
		// 3D00:84 48          STY IOBPL       ;UPON ENTRY, A&Y POINT AT THE
		// 3D02:85 49          STA IOBPH       ;I/O CONTROL BLOCK (IOB)
		//
		_memory[0x3d04] = 0xad;		// lda $c0n1 (soft-switch #1)
		_memory[0x3d05] = 0x81 + 16*DISKII_SLOT;
		_memory[0x3d06] = 0xc0;
		_memory[0x3d07] = 0x18;		// clc (= success)
		_memory[0x3d08] = 0x60;		// rts
	}
	return 0x00;
}

uint8_t DiskII::boot2(Memory::address rwts) {
		
	Memory::address iobp = _memory[IOBP] | (_memory[IOBP+1] << 8);
	uint8_t drive_id = _memory[iobp + 0x02] - 1;
	uint8_t vol = _memory[iobp + 0x03];
	uint8_t track = _memory[iobp + 0x04];
	uint8_t sector = _memory[iobp + 0x05];
	uint8_t cmd = _memory[iobp + 0x0c];
	Memory::address buf = _memory[iobp + 8] | (_memory[iobp + 9] << 8);
	DBG_DISK("boot2: cmd=%d drive=%d vol=%d %02x %02x %04x", cmd, drive_id, vol, track, sector, buf);

	flash_file *drive = _drives[drive_id];
	if (!*drive) {
		_memory[iobp + 0x0d] = DRIVE_ERROR;
		_memory[rwts + 0x07] = 0x38;	// sec (= error)
		return 0x01;
	}
	if (vol != 0 && vol != _vols[drive_id]) {
		_memory[iobp + 0x0d] = VOLUME_ERROR;
		_memory[iobp + 0x0e] = _vols[drive_id];
		_memory[rwts + 0x07] = 0x38;	// sec (= error)
		return 0x01;
	}

	seek(drive, track, sector);
	if (cmd == CMD_READ) {
		read(drive, buf, BYTES_PER_SECTOR);
		if (track == 17 && sector == 0)
			_vols[drive_id] = _memory[buf + 6];

	} else if (cmd == CMD_WRITE) {
		if (track == 17 && sector == 0)
			_vols[drive_id] = _memory[buf + 6];
		write(drive, buf, BYTES_PER_SECTOR);

	} else if (cmd != CMD_SEEK && cmd != CMD_FORMAT)
		DBG_DISK("unhandled command %d", cmd);

	_memory[iobp + 0x0d] = NO_ERROR;
	_memory[iobp + 0x0e] = _vols[drive_id];
	_memory[rwts + 0x07] = 0x18;		// clc (= success)
	return 0x00;
}

DiskII::Switches::operator uint8_t() {

	switch (_acc & 0x0f) {
	case 0x00:
		return _disk.boot1();
	case 0x01:
		// $3d00 is RWTS in BOOT2, $bd00 is same, after relocation
		return _disk.boot2(_cpu.pc() & 0xff00);
	}
	DBG_DISK("unhandled switch %04x", _acc);
	return 0x01;	// error
}