devfloppy.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

		timedsleep(return0, 0, 750);

		/* clear any pending interrupts */
		floppysense();
	}

	/* set transfer rate */
	if(fl.rate != dp->t->rate){
		fl.rate = dp->t->rate;
		outb(Pdsr, fl.rate);
	}

	/* get drive to a known cylinder */
	if(dp->confused)
		for(tries = 0; tries < 4; tries++)
			if(floppyrecal(dp) >= 0)
				break;
	dp->lasttouched = m->ticks;
	fl.selected = dp;
	if(dp->confused)
		return -1;
	return 0;
}

/*
 *  stop the floppy if it hasn't been used in 5 seconds
 */
static void
floppyoff(FDrive *dp)
{
	fl.motor &= ~MOTORBIT(dp->dev);
	outb(Pdor, fl.motor | Fintena | Fena | dp->dev);
}

/*
 *  send a command to the floppy
 */
static int
floppycmd(void)
{
	int i;
	int tries;

	fl.nstat = 0;
	for(i = 0; i < fl.ncmd; i++){
		for(tries = 0; ; tries++){
			if((inb(Pmsr)&(Ffrom|Fready)) == Fready)
				break;
			if(tries > 1000){
				DPRINT("cmd %ux can't be sent (%d)\n", fl.cmd[0], i);
				fldump();

				/* empty fifo, might have been a bad command */
				floppyresult();
				return -1;
			}
			microdelay(1);
		}
		outb(Pfdata, fl.cmd[i]);
	}
	return 0;
}

/*
 *  get a command result from the floppy
 *
 *  when the controller goes ready waiting for a command
 *  (instead of sending results), we're done
 * 
 */
static int
floppyresult(void)
{
	int i, s;
	int tries;

	/* get the result of the operation */
	for(i = 0; i < sizeof(fl.stat); i++){
		/* wait for status byte */
		for(tries = 0; ; tries++){
			s = inb(Pmsr)&(Ffrom|Fready);
			if(s == Fready){
				fl.nstat = i;
				return fl.nstat;
			}
			if(s == (Ffrom|Fready))
				break;
			if(tries > 1000){
				DPRINT("floppyresult: %d stats\n", i);
				fldump();
				fl.confused = 1;
				return -1;
			}
			microdelay(1);
		}
		fl.stat[i] = inb(Pfdata);
	}
	fl.nstat = sizeof(fl.stat);
	return fl.nstat;
}

/*
 *  calculate physical address of a logical byte offset into the disk
 *
 *  truncate dp->length if it crosses a track boundary
 */
static void
floppypos(FDrive *dp, long off)
{
	int lsec;
	int ltrack;
	int end;

	lsec = off/dp->t->bytes;
	ltrack = lsec/dp->t->sectors;
	dp->tcyl = ltrack/dp->t->heads;
	dp->tsec = (lsec % dp->t->sectors) + 1;
	dp->thead = (lsec/dp->t->sectors) % dp->t->heads;

	/*
	 *  can't read across track boundaries.
	 *  if so, decrement the bytes to be read.
	 */
	end = (ltrack+1)*dp->t->sectors*dp->t->bytes;
	if(off+dp->len > end)
		dp->len = end - off;
}

/*
 *  get the interrupt cause from the floppy.
 */
static int
floppysense(void)
{
	fl.ncmd = 0;
	fl.cmd[fl.ncmd++] = Fsense;
	if(floppycmd() < 0)
		return -1;
	if(floppyresult() < 2){
		DPRINT("can't read sense response\n");
		fldump();
		fl.confused = 1;
		return -1;
	}
	return 0;
}

static int
cmddone(void *a)
{
	USED(a);
	return fl.ncmd == 0;
}

/*
 *  Wait for a floppy interrupt.  If none occurs in 5 seconds, we
 *  may have missed one.  This only happens on some portables which
 *  do power management behind our backs.  Call the interrupt
 *  routine to try to clear any conditions.
 */
static void
floppywait(int slow)
{
	timedsleep(cmddone, 0, slow ? 5000 : 1000);
	if(!cmddone(0)){
		floppyintr(0);
		fl.confused = 1;
	}
}

/*
 *  we've lost the floppy position, go to cylinder 0.
 */
static int
floppyrecal(FDrive *dp)
{
	dp->ccyl = -1;
	dp->cyl = -1;

	fl.ncmd = 0;
	fl.cmd[fl.ncmd++] = Frecal;
	fl.cmd[fl.ncmd++] = dp->dev;
	if(floppycmd() < 0)
		return -1;
	floppywait(1);
	if(fl.nstat < 2){
		DPRINT("recalibrate: confused %ux\n", inb(Pmsr));
		fl.confused = 1;
		return -1;
	}
	if((fl.stat[0] & (Codemask|Seekend)) != Seekend){
		DPRINT("recalibrate: failed\n");
		dp->confused = 1;
		return -1;
	}
	dp->cyl = fl.stat[1];
	if(dp->cyl != 0){
		DPRINT("recalibrate: wrong cylinder %d\n", dp->cyl);
		dp->cyl = -1;
		dp->confused = 1;
		return -1;
	}

	dp->confused = 0;
	return 0;
}

/*
 *  if the controller or a specific drive is in a confused state,
 *  reset it and get back to a kown state
 */
static void
floppyrevive(void)
{
	FDrive *dp;

	/*
	 *  reset the controller if it's confused
	 */
	if(fl.confused){
		DPRINT("floppyrevive in\n");
		fldump();

		/* reset controller and turn all motors off */
		splhi();
		fl.ncmd = 1;
		fl.cmd[0] = 0;
		outb(Pdor, 0);
		delay(10);
		outb(Pdor, Fintena|Fena);
		delay(10);
		spllo();
		fl.motor = 0;
		fl.confused = 0;
		floppywait(0);

		/* mark all drives in an unknown state */
		for(dp = fl.d; dp < &fl.d[fl.ndrive]; dp++)
			dp->confused = 1;

		/* set rate to a known value */
		outb(Pdsr, 0);
		fl.rate = 0;

		DPRINT("floppyrevive out\n");
		fldump();
	}
}

/*
 *  seek to the target cylinder
 *
 *	interrupt, no results
 */
static vlong
pcfloppyseek(FDrive *dp, vlong off)
{
	floppypos(dp, off);
	if(dp->cyl == dp->tcyl){
		dp->offset = off;
		return off;
	}
	dp->cyl = -1;

	fl.ncmd = 0;
	fl.cmd[fl.ncmd++] = Fseek;
	fl.cmd[fl.ncmd++] = (dp->thead<<2) | dp->dev;
	fl.cmd[fl.ncmd++] = dp->tcyl * dp->t->steps;
	if(floppycmd() < 0)
		return -1;
	floppywait(1);
	if(fl.nstat < 2){
		DPRINT("seek: confused\n");
		fl.confused = 1;
		return -1;
	}
	if((fl.stat[0] & (Codemask|Seekend)) != Seekend){
		DPRINT("seek: failed\n");
		dp->confused = 1;
		return -1;
	}

	dp->cyl = dp->tcyl;
	dp->offset = off;
	DPRINT("seek to %d succeeded\n", dp->offset);

	return dp->offset;
}

/*
 *  read or write to floppy.  try up to three times.
 */
static long
floppyxfer(FDrive *dp, int cmd, void *a, long off, long n)
{
	long offset;
	int tries;

	if(off >= dp->t->cap)
		return 0;
	if(off + n > dp->t->cap)
		n = dp->t->cap - off;

	/* retry on error (until it gets ridiculous) */
	for(tries = 0; tries < dp->maxtries; tries++){

		dp->len = n;
		if(pcfloppyseek(dp, off) < 0){
			DPRINT("xfer: seek failed\n");
			dp->confused = 1;
			continue;
		}

		/*
		 *  set up the dma (dp->len may be trimmed)
		 */
		dp->len = dmasetup(DMAchan, a, dp->len, cmd==Fread);
		if(dp->len < 0){
	buggery:
			dmaend(DMAchan);
			continue;
		}
	
		/*
		 *  start operation
		 */
		fl.ncmd = 0;
		fl.cmd[fl.ncmd++] = cmd | (dp->t->heads > 1 ? Fmulti : 0);
		fl.cmd[fl.ncmd++] = (dp->thead<<2) | dp->dev;
		fl.cmd[fl.ncmd++] = dp->tcyl;
		fl.cmd[fl.ncmd++] = dp->thead;
		fl.cmd[fl.ncmd++] = dp->tsec;
		fl.cmd[fl.ncmd++] = dp->t->bcode;
		fl.cmd[fl.ncmd++] = dp->t->sectors;
		fl.cmd[fl.ncmd++] = dp->t->gpl;
		fl.cmd[fl.ncmd++] = 0xFF;
		if(floppycmd() < 0)
			goto buggery;

		/*
		 *  give bus to DMA, floppyintr() will read result
		 */
		floppywait(0);
		dmaend(DMAchan);

		/*
		 *  check for errors
		 */
		if(fl.nstat < 7){
			DPRINT("xfer: confused\n");
			fl.confused = 1;
			continue;
		}
		if((fl.stat[0] & Codemask)!=0 || fl.stat[1] || fl.stat[2]){
			DPRINT("xfer: failed %ux %ux %ux\n", fl.stat[0],
				fl.stat[1], fl.stat[2]);
			DPRINT("offset %lud len %ld\n", off, dp->len);
			if((fl.stat[0]&Codemask)==Cmdexec && fl.stat[1]==Overrun){
				DPRINT("DMA overrun: retry\n");
			} else
				dp->confused = 1;
			continue;
		}

		/*
		 *  check for correct cylinder
		 */
		offset = fl.stat[3] * dp->t->heads + fl.stat[4];
		offset = offset*dp->t->sectors + fl.stat[5] - 1;
		offset = offset * c2b[fl.stat[6]];
		if(offset != off+dp->len){
			DPRINT("xfer: ends on wrong cyl\n");
			dp->confused = 1;
			continue;
		}
	
		dp->lasttouched = m->ticks;
		dp->maxtries = 20;
		return dp->len;
	}

	return -1;
}

/*
void
floppymemwrite(void)
{
	int i;
	int n;
	uchar *a;
	FDrive *dp;

	dp = &fl.d[0];
	a = (uchar*)0x80000000;
	n = 0;
	while(n < 1440*1024){
		i = floppyxfer(dp, Fwrite, a+n, n, 1440*1024-n);
		if(i <= 0)
			break;
		n += i;
	}
	print("floppymemwrite wrote %d bytes\n", n);
splhi(); for(;;);
}
*/

static void
floppyintr(Ureg *ur)
{
	USED(ur);
	switch(fl.cmd[0]&~Fmulti){
	case Fread:
	case Fwrite:
	case Fformat:
	case Fdumpreg: 
		floppyresult();
		break;
	case Fseek:
	case Frecal:
	default:
		floppysense();	/* to clear interrupt */
		break;
	}
	fl.ncmd = 0;
}