amiflop.c 46.1 KB
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/*
 *  linux/amiga/amiflop.c
 *
 *  Copyright (C) 1993  Greg Harp
 *  Portions of this driver are based on code contributed by Brad Pepers
 *  
 *  revised 28.5.95 by Joerg Dorchain
 *  - now no bugs(?) any more for both HD & DD
 *  - added support for 40 Track 5.25" drives, 80-track hopefully behaves
 *    like 3.5" dd (no way to test - are there any 5.25" drives out there
 *    that work on an A4000?)
 *  - wrote formatting routine (maybe dirty, but works)
 *
 *  june/july 1995 added ms-dos support by Joerg Dorchain
 *  (portions based on messydos.device and various contributors)
 *  - currently only 9 and 18 sector disks
 *
 *  - fixed a bug with the internal trackbuffer when using multiple 
 *    disks the same time
 *  - made formatting a bit safer
 *  - added command line and machine based default for "silent" df0
 *
 *  december 1995 adapted for 1.2.13pl4 by Joerg Dorchain
 *  - works but I think it's inefficient. (look in redo_fd_request)
 *    But the changes were very efficient. (only three and a half lines)
 *
 *  january 1996 added special ioctl for tracking down read/write problems
 *  - usage ioctl(d, RAW_TRACK, ptr); the raw track buffer (MFM-encoded data
 *    is copied to area. (area should be large enough since no checking is
 *    done - 30K is currently sufficient). return the actual size of the
 *    trackbuffer
 *  - replaced udelays() by a timer (CIAA timer B) for the waits 
 *    needed for the disk mechanic.
 *
 *  february 1996 fixed error recovery and multiple disk access
 *  - both got broken the first time I tampered with the driver :-(
 *  - still not safe, but better than before
 *
 *  revised Marts 3rd, 1996 by Jes Sorensen for use in the 1.3.28 kernel.
 *  - Minor changes to accept the kdev_t.
 *  - Replaced some more udelays with ms_delays. Udelay is just a loop,
 *    and so the delay will be different depending on the given
 *    processor :-(
 *  - The driver could use a major cleanup because of the new
 *    major/minor handling that came with kdev_t. It seems to work for
 *    the time being, but I can't guarantee that it will stay like
 *    that when we start using 16 (24?) bit minors.
 *
 * restructured jan 1997 by Joerg Dorchain
 * - Fixed Bug accessing multiple disks
 * - some code cleanup
 * - added trackbuffer for each drive to speed things up
 * - fixed some race conditions (who finds the next may send it to me ;-)
 */

#include <linux/module.h>

#include <linux/fd.h>
#include <linux/hdreg.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/amifdreg.h>
#include <linux/amifd.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>

#include <asm/setup.h>
#include <asm/uaccess.h>
#include <asm/amigahw.h>
#include <asm/amigaints.h>
#include <asm/irq.h>

#undef DEBUG /* print _LOTS_ of infos */

#define RAW_IOCTL
#ifdef RAW_IOCTL
#define IOCTL_RAW_TRACK 0x5254524B  /* 'RTRK' */
#endif

/*
 *  Defines
 */

/*
 *  Error codes
 */
#define FD_OK		0	/* operation succeeded */
#define FD_ERROR	-1	/* general error (seek, read, write, etc) */
#define FD_NOUNIT	1	/* unit does not exist */
#define FD_UNITBUSY	2	/* unit already active */
#define FD_NOTACTIVE	3	/* unit is not active */
#define FD_NOTREADY	4	/* unit is not ready (motor not on/no disk) */

#define MFM_NOSYNC	1
#define MFM_HEADER	2
#define MFM_DATA	3
#define MFM_TRACK	4

/*
 *  Floppy ID values
 */
#define FD_NODRIVE	0x00000000  /* response when no unit is present */
#define FD_DD_3 	0xffffffff  /* double-density 3.5" (880K) drive */
#define FD_HD_3 	0x55555555  /* high-density 3.5" (1760K) drive */
#define FD_DD_5 	0xaaaaaaaa  /* double-density 5.25" (440K) drive */

static unsigned long int fd_def_df0 = FD_DD_3;     /* default for df0 if it doesn't identify */

module_param(fd_def_df0, ulong, 0);
MODULE_LICENSE("GPL");

static struct request_queue *floppy_queue;
#define QUEUE (floppy_queue)
#define CURRENT elv_next_request(floppy_queue)

/*
 *  Macros
 */
#define MOTOR_ON	(ciab.prb &= ~DSKMOTOR)
#define MOTOR_OFF	(ciab.prb |= DSKMOTOR)
#define SELECT(mask)    (ciab.prb &= ~mask)
#define DESELECT(mask)  (ciab.prb |= mask)
#define SELMASK(drive)  (1 << (3 + (drive & 3)))

static struct fd_drive_type drive_types[] = {
/*  code	name	   tr he   rdsz   wrsz sm pc1 pc2 sd  st st*/
/*  warning: times are now in milliseconds (ms)                    */
{ FD_DD_3,	"DD 3.5",  80, 2, 14716, 13630, 1, 80,161, 3, 18, 1},
{ FD_HD_3,	"HD 3.5",  80, 2, 28344, 27258, 2, 80,161, 3, 18, 1},
{ FD_DD_5,	"DD 5.25", 40, 2, 14716, 13630, 1, 40, 81, 6, 30, 2},
{ FD_NODRIVE, "No Drive", 0, 0,     0,     0, 0,  0,  0,  0,  0, 0}
};
134
static int num_dr_types = ARRAY_SIZE(drive_types);
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static int amiga_read(int), dos_read(int);
static void amiga_write(int), dos_write(int);
static struct fd_data_type data_types[] = {
	{ "Amiga", 11 , amiga_read, amiga_write},
	{ "MS-Dos", 9, dos_read, dos_write}
};

/* current info on each unit */
static struct amiga_floppy_struct unit[FD_MAX_UNITS];

static struct timer_list flush_track_timer[FD_MAX_UNITS];
static struct timer_list post_write_timer;
static struct timer_list motor_on_timer;
static struct timer_list motor_off_timer[FD_MAX_UNITS];
static int on_attempts;

/* Synchronization of FDC access */
/* request loop (trackbuffer) */
static volatile int fdc_busy = -1;
static volatile int fdc_nested;
static DECLARE_WAIT_QUEUE_HEAD(fdc_wait);
 
static DECLARE_WAIT_QUEUE_HEAD(motor_wait);

static volatile int selected = -1;	/* currently selected drive */

static int writepending;
static int writefromint;
static char *raw_buf;

static DEFINE_SPINLOCK(amiflop_lock);

#define RAW_BUF_SIZE 30000  /* size of raw disk data */

/*
 * These are global variables, as that's the easiest way to give
 * information to interrupts. They are the data used for the current
 * request.
 */
static volatile char block_flag;
static DECLARE_WAIT_QUEUE_HEAD(wait_fd_block);

/* MS-Dos MFM Coding tables (should go quick and easy) */
static unsigned char mfmencode[16]={
	0x2a, 0x29, 0x24, 0x25, 0x12, 0x11, 0x14, 0x15,
	0x4a, 0x49, 0x44, 0x45, 0x52, 0x51, 0x54, 0x55
};
static unsigned char mfmdecode[128];

/* floppy internal millisecond timer stuff */
static volatile int ms_busy = -1;
static DECLARE_WAIT_QUEUE_HEAD(ms_wait);
#define MS_TICKS ((amiga_eclock+50)/1000)

/*
 * Note that MAX_ERRORS=X doesn't imply that we retry every bad read
 * max X times - some types of errors increase the errorcount by 2 or
 * even 3, so we might actually retry only X/2 times before giving up.
 */
#define MAX_ERRORS 12

/* Prevent "aliased" accesses. */
static int fd_ref[4] = { 0,0,0,0 };
static int fd_device[4] = { 0, 0, 0, 0 };

/*
 * Here come the actual hardware access and helper functions.
 * They are not reentrant and single threaded because all drives
 * share the same hardware and the same trackbuffer.
 */

/* Milliseconds timer */

static irqreturn_t ms_isr(int irq, void *dummy, struct pt_regs *fp)
{
	ms_busy = -1;
	wake_up(&ms_wait);
	return IRQ_HANDLED;
}

/* all waits are queued up 
   A more generic routine would do a schedule a la timer.device */
static void ms_delay(int ms)
{
	unsigned long flags;
	int ticks;
	if (ms > 0) {
		local_irq_save(flags);
		while (ms_busy == 0)
			sleep_on(&ms_wait);
		ms_busy = 0;
		local_irq_restore(flags);
		ticks = MS_TICKS*ms-1;
		ciaa.tblo=ticks%256;
		ciaa.tbhi=ticks/256;
		ciaa.crb=0x19; /*count eclock, force load, one-shoot, start */
		sleep_on(&ms_wait);
	}
}

/* Hardware semaphore */

/* returns true when we would get the semaphore */
static inline int try_fdc(int drive)
{
	drive &= 3;
	return ((fdc_busy < 0) || (fdc_busy == drive));
}

static void get_fdc(int drive)
{
	unsigned long flags;

	drive &= 3;
#ifdef DEBUG
	printk("get_fdc: drive %d  fdc_busy %d  fdc_nested %d\n",drive,fdc_busy,fdc_nested);
#endif
	local_irq_save(flags);
	while (!try_fdc(drive))
		sleep_on(&fdc_wait);
	fdc_busy = drive;
	fdc_nested++;
	local_irq_restore(flags);
}

static inline void rel_fdc(void)
{
#ifdef DEBUG
	if (fdc_nested == 0)
		printk("fd: unmatched rel_fdc\n");
	printk("rel_fdc: fdc_busy %d fdc_nested %d\n",fdc_busy,fdc_nested);
#endif
	fdc_nested--;
	if (fdc_nested == 0) {
		fdc_busy = -1;
		wake_up(&fdc_wait);
	}
}

static void fd_select (int drive)
{
	unsigned char prb = ~0;

	drive&=3;
#ifdef DEBUG
	printk("selecting %d\n",drive);
#endif
	if (drive == selected)
		return;
	get_fdc(drive);
	selected = drive;

	if (unit[drive].track % 2 != 0)
		prb &= ~DSKSIDE;
	if (unit[drive].motor == 1)
		prb &= ~DSKMOTOR;
	ciab.prb |= (SELMASK(0)|SELMASK(1)|SELMASK(2)|SELMASK(3));
	ciab.prb = prb;
	prb &= ~SELMASK(drive);
	ciab.prb = prb;
	rel_fdc();
}

static void fd_deselect (int drive)
{
	unsigned char prb;
	unsigned long flags;

	drive&=3;
#ifdef DEBUG
	printk("deselecting %d\n",drive);
#endif
	if (drive != selected) {
		printk(KERN_WARNING "Deselecting drive %d while %d was selected!\n",drive,selected);
		return;
	}

	get_fdc(drive);
	local_irq_save(flags);

	selected = -1;

	prb = ciab.prb;
	prb |= (SELMASK(0)|SELMASK(1)|SELMASK(2)|SELMASK(3));
	ciab.prb = prb;

	local_irq_restore (flags);
	rel_fdc();

}

static void motor_on_callback(unsigned long nr)
{
	if (!(ciaa.pra & DSKRDY) || --on_attempts == 0) {
		wake_up (&motor_wait);
	} else {
		motor_on_timer.expires = jiffies + HZ/10;
		add_timer(&motor_on_timer);
	}
}

static int fd_motor_on(int nr)
{
	nr &= 3;

	del_timer(motor_off_timer + nr);

	if (!unit[nr].motor) {
		unit[nr].motor = 1;
		fd_select(nr);

		motor_on_timer.data = nr;
		mod_timer(&motor_on_timer, jiffies + HZ/2);

		on_attempts = 10;
		sleep_on (&motor_wait);
		fd_deselect(nr);
	}

	if (on_attempts == 0) {
		on_attempts = -1;
#if 0
		printk (KERN_ERR "motor_on failed, turning motor off\n");
		fd_motor_off (nr);
		return 0;
#else
		printk (KERN_WARNING "DSKRDY not set after 1.5 seconds - assuming drive is spinning notwithstanding\n");
#endif
	}

	return 1;
}

static void fd_motor_off(unsigned long drive)
{
	long calledfromint;
#ifdef MODULE
	long decusecount;

	decusecount = drive & 0x40000000;
#endif
	calledfromint = drive & 0x80000000;
	drive&=3;
	if (calledfromint && !try_fdc(drive)) {
		/* We would be blocked in an interrupt, so try again later */
		motor_off_timer[drive].expires = jiffies + 1;
		add_timer(motor_off_timer + drive);
		return;
	}
	unit[drive].motor = 0;
	fd_select(drive);
	udelay (1);
	fd_deselect(drive);
}

static void floppy_off (unsigned int nr)
{
	int drive;

	drive = nr & 3;
	/* called this way it is always from interrupt */
	motor_off_timer[drive].data = nr | 0x80000000;
	mod_timer(motor_off_timer + drive, jiffies + 3*HZ);
}

static int fd_calibrate(int drive)
{
	unsigned char prb;
	int n;

	drive &= 3;
	get_fdc(drive);
	if (!fd_motor_on (drive))
		return 0;
	fd_select (drive);
	prb = ciab.prb;
	prb |= DSKSIDE;
	prb &= ~DSKDIREC;
	ciab.prb = prb;
	for (n = unit[drive].type->tracks/2; n != 0; --n) {
		if (ciaa.pra & DSKTRACK0)
			break;
		prb &= ~DSKSTEP;
		ciab.prb = prb;
		prb |= DSKSTEP;
		udelay (2);
		ciab.prb = prb;
		ms_delay(unit[drive].type->step_delay);
	}
	ms_delay (unit[drive].type->settle_time);
	prb |= DSKDIREC;
	n = unit[drive].type->tracks + 20;
	for (;;) {
		prb &= ~DSKSTEP;
		ciab.prb = prb;
		prb |= DSKSTEP;
		udelay (2);
		ciab.prb = prb;
		ms_delay(unit[drive].type->step_delay + 1);
		if ((ciaa.pra & DSKTRACK0) == 0)
			break;
		if (--n == 0) {
			printk (KERN_ERR "fd%d: calibrate failed, turning motor off\n", drive);
			fd_motor_off (drive);
			unit[drive].track = -1;
			rel_fdc();
			return 0;
		}
	}
	unit[drive].track = 0;
	ms_delay(unit[drive].type->settle_time);

	rel_fdc();
	fd_deselect(drive);
	return 1;
}

static int fd_seek(int drive, int track)
{
	unsigned char prb;
	int cnt;

#ifdef DEBUG
	printk("seeking drive %d to track %d\n",drive,track);
#endif
	drive &= 3;
	get_fdc(drive);
	if (unit[drive].track == track) {
		rel_fdc();
		return 1;
	}
	if (!fd_motor_on(drive)) {
		rel_fdc();
		return 0;
	}
	if (unit[drive].track < 0 && !fd_calibrate(drive)) {
		rel_fdc();
		return 0;
	}

	fd_select (drive);
	cnt = unit[drive].track/2 - track/2;
	prb = ciab.prb;
	prb |= DSKSIDE | DSKDIREC;
	if (track % 2 != 0)
		prb &= ~DSKSIDE;
	if (cnt < 0) {
		cnt = - cnt;
		prb &= ~DSKDIREC;
	}
	ciab.prb = prb;
	if (track % 2 != unit[drive].track % 2)
		ms_delay (unit[drive].type->side_time);
	unit[drive].track = track;
	if (cnt == 0) {
		rel_fdc();
		fd_deselect(drive);
		return 1;
	}
	do {
		prb &= ~DSKSTEP;
		ciab.prb = prb;
		prb |= DSKSTEP;
		udelay (1);
		ciab.prb = prb;
		ms_delay (unit[drive].type->step_delay);
	} while (--cnt != 0);
	ms_delay (unit[drive].type->settle_time);

	rel_fdc();
	fd_deselect(drive);
	return 1;
}

static unsigned long fd_get_drive_id(int drive)
{
	int i;
	ulong id = 0;

  	drive&=3;
  	get_fdc(drive);
	/* set up for ID */
	MOTOR_ON;
	udelay(2);
	SELECT(SELMASK(drive));
	udelay(2);
	DESELECT(SELMASK(drive));
	udelay(2);
	MOTOR_OFF;
	udelay(2);
	SELECT(SELMASK(drive));
	udelay(2);
	DESELECT(SELMASK(drive));
	udelay(2);

	/* loop and read disk ID */
	for (i=0; i<32; i++) {
		SELECT(SELMASK(drive));
		udelay(2);

		/* read and store value of DSKRDY */
		id <<= 1;
		id |= (ciaa.pra & DSKRDY) ? 0 : 1;	/* cia regs are low-active! */

		DESELECT(SELMASK(drive));
	}

	rel_fdc();

        /*
         * RB: At least A500/A2000's df0: don't identify themselves.
         * As every (real) Amiga has at least a 3.5" DD drive as df0:
         * we default to that if df0: doesn't identify as a certain
         * type.
         */
        if(drive == 0 && id == FD_NODRIVE)
	{
                id = fd_def_df0;
                printk(KERN_NOTICE "fd: drive 0 didn't identify, setting default %08lx\n", (ulong)fd_def_df0);
	}
	/* return the ID value */
	return (id);
}

static irqreturn_t fd_block_done(int irq, void *dummy, struct pt_regs *fp)
{
	if (block_flag)
		custom.dsklen = 0x4000;

	if (block_flag == 2) { /* writing */
		writepending = 2;
		post_write_timer.expires = jiffies + 1; /* at least 2 ms */
		post_write_timer.data = selected;
		add_timer(&post_write_timer);
	}
	else {                /* reading */
		block_flag = 0;
		wake_up (&wait_fd_block);
	}
	return IRQ_HANDLED;
}

static void raw_read(int drive)
{
	drive&=3;
	get_fdc(drive);
	while (block_flag)
		sleep_on(&wait_fd_block);
	fd_select(drive);
	/* setup adkcon bits correctly */
	custom.adkcon = ADK_MSBSYNC;
	custom.adkcon = ADK_SETCLR|ADK_WORDSYNC|ADK_FAST;

	custom.dsksync = MFM_SYNC;

	custom.dsklen = 0;
	custom.dskptr = (u_char *)ZTWO_PADDR((u_char *)raw_buf);
	custom.dsklen = unit[drive].type->read_size/sizeof(short) | DSKLEN_DMAEN;
	custom.dsklen = unit[drive].type->read_size/sizeof(short) | DSKLEN_DMAEN;

	block_flag = 1;

	while (block_flag)
		sleep_on (&wait_fd_block);

	custom.dsklen = 0;
	fd_deselect(drive);
	rel_fdc();
}

static int raw_write(int drive)
{
	ushort adk;

	drive&=3;
	get_fdc(drive); /* corresponds to rel_fdc() in post_write() */
	if ((ciaa.pra & DSKPROT) == 0) {
		rel_fdc();
		return 0;
	}
	while (block_flag)
		sleep_on(&wait_fd_block);
	fd_select(drive);
	/* clear adkcon bits */
	custom.adkcon = ADK_PRECOMP1|ADK_PRECOMP0|ADK_WORDSYNC|ADK_MSBSYNC;
	/* set appropriate adkcon bits */
	adk = ADK_SETCLR|ADK_FAST;
	if ((ulong)unit[drive].track >= unit[drive].type->precomp2)
		adk |= ADK_PRECOMP1;
	else if ((ulong)unit[drive].track >= unit[drive].type->precomp1)
		adk |= ADK_PRECOMP0;
	custom.adkcon = adk;

	custom.dsklen = DSKLEN_WRITE;
	custom.dskptr = (u_char *)ZTWO_PADDR((u_char *)raw_buf);
	custom.dsklen = unit[drive].type->write_size/sizeof(short) | DSKLEN_DMAEN|DSKLEN_WRITE;
	custom.dsklen = unit[drive].type->write_size/sizeof(short) | DSKLEN_DMAEN|DSKLEN_WRITE;

	block_flag = 2;
	return 1;
}

/*
 * to be called at least 2ms after the write has finished but before any
 * other access to the hardware.
 */
static void post_write (unsigned long drive)
{
#ifdef DEBUG
	printk("post_write for drive %ld\n",drive);
#endif
	drive &= 3;
	custom.dsklen = 0;
	block_flag = 0;
	writepending = 0;
	writefromint = 0;
	unit[drive].dirty = 0;
	wake_up(&wait_fd_block);
	fd_deselect(drive);
	rel_fdc(); /* corresponds to get_fdc() in raw_write */
}


/*
 * The following functions are to convert the block contents into raw data
 * written to disk and vice versa.
 * (Add other formats here ;-))
 */

static unsigned long scan_sync(unsigned long raw, unsigned long end)
{
	ushort *ptr = (ushort *)raw, *endp = (ushort *)end;

	while (ptr < endp && *ptr++ != 0x4489)
		;
	if (ptr < endp) {
		while (*ptr == 0x4489 && ptr < endp)
			ptr++;
		return (ulong)ptr;
	}
	return 0;
}

static inline unsigned long checksum(unsigned long *addr, int len)
{
	unsigned long csum = 0;

	len /= sizeof(*addr);
	while (len-- > 0)
		csum ^= *addr++;
	csum = ((csum>>1) & 0x55555555)  ^  (csum & 0x55555555);

	return csum;
}

static unsigned long decode (unsigned long *data, unsigned long *raw,
			     int len)
{
	ulong *odd, *even;

	/* convert length from bytes to longwords */
	len >>= 2;
	odd = raw;
	even = odd + len;

	/* prepare return pointer */
	raw += len * 2;

	do {
		*data++ = ((*odd++ & 0x55555555) << 1) | (*even++ & 0x55555555);
	} while (--len != 0);

	return (ulong)raw;
}

struct header {
	unsigned char magic;
	unsigned char track;
	unsigned char sect;
	unsigned char ord;
	unsigned char labels[16];
	unsigned long hdrchk;
	unsigned long datachk;
};

static int amiga_read(int drive)
{
	unsigned long raw;
	unsigned long end;
	int scnt;
	unsigned long csum;
	struct header hdr;

	drive&=3;
	raw = (long) raw_buf;
	end = raw + unit[drive].type->read_size;

	for (scnt = 0;scnt < unit[drive].dtype->sects * unit[drive].type->sect_mult; scnt++) {
		if (!(raw = scan_sync(raw, end))) {
			printk (KERN_INFO "can't find sync for sector %d\n", scnt);
			return MFM_NOSYNC;
		}

		raw = decode ((ulong *)&hdr.magic, (ulong *)raw, 4);
		raw = decode ((ulong *)&hdr.labels, (ulong *)raw, 16);
		raw = decode ((ulong *)&hdr.hdrchk, (ulong *)raw, 4);
		raw = decode ((ulong *)&hdr.datachk, (ulong *)raw, 4);
		csum = checksum((ulong *)&hdr,
				(char *)&hdr.hdrchk-(char *)&hdr);

#ifdef DEBUG
		printk ("(%x,%d,%d,%d) (%lx,%lx,%lx,%lx) %lx %lx\n",
			hdr.magic, hdr.track, hdr.sect, hdr.ord,
			*(ulong *)&hdr.labels[0], *(ulong *)&hdr.labels[4],
			*(ulong *)&hdr.labels[8], *(ulong *)&hdr.labels[12],
			hdr.hdrchk, hdr.datachk);
#endif

		if (hdr.hdrchk != csum) {
			printk(KERN_INFO "MFM_HEADER: %08lx,%08lx\n", hdr.hdrchk, csum);
			return MFM_HEADER;
		}

		/* verify track */
		if (hdr.track != unit[drive].track) {
			printk(KERN_INFO "MFM_TRACK: %d, %d\n", hdr.track, unit[drive].track);
			return MFM_TRACK;
		}

		raw = decode ((ulong *)(unit[drive].trackbuf + hdr.sect*512),
			      (ulong *)raw, 512);
		csum = checksum((ulong *)(unit[drive].trackbuf + hdr.sect*512), 512);

		if (hdr.datachk != csum) {
			printk(KERN_INFO "MFM_DATA: (%x:%d:%d:%d) sc=%d %lx, %lx\n",
			       hdr.magic, hdr.track, hdr.sect, hdr.ord, scnt,
			       hdr.datachk, csum);
			printk (KERN_INFO "data=(%lx,%lx,%lx,%lx)\n",
				((ulong *)(unit[drive].trackbuf+hdr.sect*512))[0],
				((ulong *)(unit[drive].trackbuf+hdr.sect*512))[1],
				((ulong *)(unit[drive].trackbuf+hdr.sect*512))[2],
				((ulong *)(unit[drive].trackbuf+hdr.sect*512))[3]);
			return MFM_DATA;
		}
	}

	return 0;
}

static void encode(unsigned long data, unsigned long *dest)
{
	unsigned long data2;

	data &= 0x55555555;
	data2 = data ^ 0x55555555;
	data |= ((data2 >> 1) | 0x80000000) & (data2 << 1);

	if (*(dest - 1) & 0x00000001)
		data &= 0x7FFFFFFF;

	*dest = data;
}

static void encode_block(unsigned long *dest, unsigned long *src, int len)
{
	int cnt, to_cnt = 0;
	unsigned long data;

	/* odd bits */
	for (cnt = 0; cnt < len / 4; cnt++) {
		data = src[cnt] >> 1;
		encode(data, dest + to_cnt++);
	}

	/* even bits */
	for (cnt = 0; cnt < len / 4; cnt++) {
		data = src[cnt];
		encode(data, dest + to_cnt++);
	}
}

static unsigned long *putsec(int disk, unsigned long *raw, int cnt)
{
	struct header hdr;
	int i;

	disk&=3;
	*raw = (raw[-1]&1) ? 0x2AAAAAAA : 0xAAAAAAAA;
	raw++;
	*raw++ = 0x44894489;

	hdr.magic = 0xFF;
	hdr.track = unit[disk].track;
	hdr.sect = cnt;
	hdr.ord = unit[disk].dtype->sects * unit[disk].type->sect_mult - cnt;
	for (i = 0; i < 16; i++)
		hdr.labels[i] = 0;
	hdr.hdrchk = checksum((ulong *)&hdr,
			      (char *)&hdr.hdrchk-(char *)&hdr);
	hdr.datachk = checksum((ulong *)(unit[disk].trackbuf+cnt*512), 512);

	encode_block(raw, (ulong *)&hdr.magic, 4);
	raw += 2;
	encode_block(raw, (ulong *)&hdr.labels, 16);
	raw += 8;
	encode_block(raw, (ulong *)&hdr.hdrchk, 4);
	raw += 2;
	encode_block(raw, (ulong *)&hdr.datachk, 4);
	raw += 2;
	encode_block(raw, (ulong *)(unit[disk].trackbuf+cnt*512), 512);
	raw += 256;

	return raw;
}

static void amiga_write(int disk)
{
	unsigned int cnt;
	unsigned long *ptr = (unsigned long *)raw_buf;

	disk&=3;
	/* gap space */
	for (cnt = 0; cnt < 415 * unit[disk].type->sect_mult; cnt++)
		*ptr++ = 0xaaaaaaaa;

	/* sectors */
	for (cnt = 0; cnt < unit[disk].dtype->sects * unit[disk].type->sect_mult; cnt++)
		ptr = putsec (disk, ptr, cnt);
	*(ushort *)ptr = (ptr[-1]&1) ? 0x2AA8 : 0xAAA8;
}


struct dos_header {
	unsigned char track,   /* 0-80 */
		side,    /* 0-1 */
		sec,     /* 0-...*/
		len_desc;/* 2 */
	unsigned short crc;     /* on 68000 we got an alignment problem, 
				   but this compiler solves it  by adding silently 
				   adding a pad byte so data won't fit
				   and this took about 3h to discover.... */
	unsigned char gap1[22];     /* for longword-alignedness (0x4e) */
};

/* crc routines are borrowed from the messydos-handler  */

/* excerpt from the messydos-device           
; The CRC is computed not only over the actual data, but including
; the SYNC mark (3 * $a1) and the 'ID/DATA - Address Mark' ($fe/$fb).
; As we don't read or encode these fields into our buffers, we have to
; preload the registers containing the CRC with the values they would have
; after stepping over these fields.
;
; How CRCs "really" work:
;
; First, you should regard a bitstring as a series of coefficients of
; polynomials. We calculate with these polynomials in modulo-2
; arithmetic, in which both add and subtract are done the same as
; exclusive-or. Now, we modify our data (a very long polynomial) in
; such a way that it becomes divisible by the CCITT-standard 16-bit
;		 16   12   5
; polynomial:	x  + x	+ x + 1, represented by $11021. The easiest
; way to do this would be to multiply (using proper arithmetic) our
; datablock with $11021. So we have:
;   data * $11021		 =
;   data * ($10000 + $1021)      =
;   data * $10000 + data * $1021
; The left part of this is simple: Just add two 0 bytes. But then
; the right part (data $1021) remains difficult and even could have
; a carry into the left part. The solution is to use a modified
; multiplication, which has a result that is not correct, but with
; a difference of any multiple of $11021. We then only need to keep
; the 16 least significant bits of the result.
;
; The following algorithm does this for us:
;
;   unsigned char *data, c, crclo, crchi;
;   while (not done) {
;	c = *data++ + crchi;
;	crchi = (@ c) >> 8 + crclo;
;	crclo = @ c;
;   }
;
; Remember, + is done with EOR, the @ operator is in two tables (high
; and low byte separately), which is calculated as
;
;      $1021 * (c & $F0)
;  xor $1021 * (c & $0F)
;  xor $1021 * (c >> 4)         (* is regular multiplication)
;
;
; Anyway, the end result is the same as the remainder of the division of
; the data by $11021. I am afraid I need to study theory a bit more...


my only works was to code this from manx to C....

*/

static ushort dos_crc(void * data_a3, int data_d0, int data_d1, int data_d3)
{
	static unsigned char CRCTable1[] = {
		0x00,0x10,0x20,0x30,0x40,0x50,0x60,0x70,0x81,0x91,0xa1,0xb1,0xc1,0xd1,0xe1,0xf1,
		0x12,0x02,0x32,0x22,0x52,0x42,0x72,0x62,0x93,0x83,0xb3,0xa3,0xd3,0xc3,0xf3,0xe3,
		0x24,0x34,0x04,0x14,0x64,0x74,0x44,0x54,0xa5,0xb5,0x85,0x95,0xe5,0xf5,0xc5,0xd5,
		0x36,0x26,0x16,0x06,0x76,0x66,0x56,0x46,0xb7,0xa7,0x97,0x87,0xf7,0xe7,0xd7,0xc7,
		0x48,0x58,0x68,0x78,0x08,0x18,0x28,0x38,0xc9,0xd9,0xe9,0xf9,0x89,0x99,0xa9,0xb9,
		0x5a,0x4a,0x7a,0x6a,0x1a,0x0a,0x3a,0x2a,0xdb,0xcb,0xfb,0xeb,0x9b,0x8b,0xbb,0xab,
		0x6c,0x7c,0x4c,0x5c,0x2c,0x3c,0x0c,0x1c,0xed,0xfd,0xcd,0xdd,0xad,0xbd,0x8d,0x9d,
		0x7e,0x6e,0x5e,0x4e,0x3e,0x2e,0x1e,0x0e,0xff,0xef,0xdf,0xcf,0xbf,0xaf,0x9f,0x8f,
		0x91,0x81,0xb1,0xa1,0xd1,0xc1,0xf1,0xe1,0x10,0x00,0x30,0x20,0x50,0x40,0x70,0x60,
		0x83,0x93,0xa3,0xb3,0xc3,0xd3,0xe3,0xf3,0x02,0x12,0x22,0x32,0x42,0x52,0x62,0x72,
		0xb5,0xa5,0x95,0x85,0xf5,0xe5,0xd5,0xc5,0x34,0x24,0x14,0x04,0x74,0x64,0x54,0x44,
		0xa7,0xb7,0x87,0x97,0xe7,0xf7,0xc7,0xd7,0x26,0x36,0x06,0x16,0x66,0x76,0x46,0x56,
		0xd9,0xc9,0xf9,0xe9,0x99,0x89,0xb9,0xa9,0x58,0x48,0x78,0x68,0x18,0x08,0x38,0x28,
		0xcb,0xdb,0xeb,0xfb,0x8b,0x9b,0xab,0xbb,0x4a,0x5a,0x6a,0x7a,0x0a,0x1a,0x2a,0x3a,
		0xfd,0xed,0xdd,0xcd,0xbd,0xad,0x9d,0x8d,0x7c,0x6c,0x5c,0x4c,0x3c,0x2c,0x1c,0x0c,
		0xef,0xff,0xcf,0xdf,0xaf,0xbf,0x8f,0x9f,0x6e,0x7e,0x4e,0x5e,0x2e,0x3e,0x0e,0x1e
	};

	static unsigned char CRCTable2[] = {
		0x00,0x21,0x42,0x63,0x84,0xa5,0xc6,0xe7,0x08,0x29,0x4a,0x6b,0x8c,0xad,0xce,0xef,
		0x31,0x10,0x73,0x52,0xb5,0x94,0xf7,0xd6,0x39,0x18,0x7b,0x5a,0xbd,0x9c,0xff,0xde,
		0x62,0x43,0x20,0x01,0xe6,0xc7,0xa4,0x85,0x6a,0x4b,0x28,0x09,0xee,0xcf,0xac,0x8d,
		0x53,0x72,0x11,0x30,0xd7,0xf6,0x95,0xb4,0x5b,0x7a,0x19,0x38,0xdf,0xfe,0x9d,0xbc,
		0xc4,0xe5,0x86,0xa7,0x40,0x61,0x02,0x23,0xcc,0xed,0x8e,0xaf,0x48,0x69,0x0a,0x2b,
		0xf5,0xd4,0xb7,0x96,0x71,0x50,0x33,0x12,0xfd,0xdc,0xbf,0x9e,0x79,0x58,0x3b,0x1a,
		0xa6,0x87,0xe4,0xc5,0x22,0x03,0x60,0x41,0xae,0x8f,0xec,0xcd,0x2a,0x0b,0x68,0x49,
		0x97,0xb6,0xd5,0xf4,0x13,0x32,0x51,0x70,0x9f,0xbe,0xdd,0xfc,0x1b,0x3a,0x59,0x78,
		0x88,0xa9,0xca,0xeb,0x0c,0x2d,0x4e,0x6f,0x80,0xa1,0xc2,0xe3,0x04,0x25,0x46,0x67,
		0xb9,0x98,0xfb,0xda,0x3d,0x1c,0x7f,0x5e,0xb1,0x90,0xf3,0xd2,0x35,0x14,0x77,0x56,
		0xea,0xcb,0xa8,0x89,0x6e,0x4f,0x2c,0x0d,0xe2,0xc3,0xa0,0x81,0x66,0x47,0x24,0x05,
		0xdb,0xfa,0x99,0xb8,0x5f,0x7e,0x1d,0x3c,0xd3,0xf2,0x91,0xb0,0x57,0x76,0x15,0x34,
		0x4c,0x6d,0x0e,0x2f,0xc8,0xe9,0x8a,0xab,0x44,0x65,0x06,0x27,0xc0,0xe1,0x82,0xa3,
		0x7d,0x5c,0x3f,0x1e,0xf9,0xd8,0xbb,0x9a,0x75,0x54,0x37,0x16,0xf1,0xd0,0xb3,0x92,
		0x2e,0x0f,0x6c,0x4d,0xaa,0x8b,0xe8,0xc9,0x26,0x07,0x64,0x45,0xa2,0x83,0xe0,0xc1,
		0x1f,0x3e,0x5d,0x7c,0x9b,0xba,0xd9,0xf8,0x17,0x36,0x55,0x74,0x93,0xb2,0xd1,0xf0
	};

/* look at the asm-code - what looks in C a bit strange is almost as good as handmade */
	register int i;
	register unsigned char *CRCT1, *CRCT2, *data, c, crch, crcl;

	CRCT1=CRCTable1;
	CRCT2=CRCTable2;
	data=data_a3;
	crcl=data_d1;
	crch=data_d0;
	for (i=data_d3; i>=0; i--) {
		c = (*data++) ^ crch;
		crch = CRCT1[c] ^ crcl;
		crcl = CRCT2[c];
	}
	return (crch<<8)|crcl;
}

static inline ushort dos_hdr_crc (struct dos_header *hdr)
{
	return dos_crc(&(hdr->track), 0xb2, 0x30, 3); /* precomputed magic */
}

static inline ushort dos_data_crc(unsigned char *data)
{
	return dos_crc(data, 0xe2, 0x95 ,511); /* precomputed magic */
}