simh-testsetgenerator/Interdata/id_mt.c

/* id_mt.c: Interdata magnetic tape simulator

   Copyright (c) 2001-2002, Robert M Supnik

   Permission is hereby granted, free of charge, to any person obtaining a
   copy of this software and associated documentation files (the "Software"),
   to deal in the Software without restriction, including without limitation
   the rights to use, copy, modify, merge, publish, distribute, sublicense,
   and/or sell copies of the Software, and to permit persons to whom the
   Software is furnished to do so, subject to the following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   ROBERT M SUPNIK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

   Except as contained in this notice, the name of Robert M Supnik shall not
   be used in advertising or otherwise to promote the sale, use or other dealings
   in this Software without prior written authorization from Robert M Supnik.

   mt		M46-494 dual density 9-track magtape controller

   Magnetic tapes are represented as a series of variable 8b records
   of the form:

	32b record length in bytes - exact number
	byte 0
	byte 1
	:
	byte n-2
	byte n-1
	32b record length in bytes - exact number

   If the byte count is odd, the record is padded with an extra byte
   of junk.  File marks are represented by a single record length of 0.
   End of tape is two consecutive end of file marks.
*/

#include "id_defs.h"

#define UNIT_V_WLK	(UNIT_V_UF + 0)			/* write locked */
#define UNIT_V_PNU	(UNIT_V_UF + 1)			/* pos not updated */
#define UNIT_WLK	(1 << UNIT_V_WLK)
#define UNIT_PNU	(1 << UNIT_V_PNU)
#define UST		u3				/* unit status */
#define UCMD		u4				/* unit command */
#define MT_MAXFR	(1 << 16)			/* max transfer */
#define UNIT_WPRT	(UNIT_WLK | UNIT_RO)		/* write protect */

/* Command - in UCMD */

#define MTC_SPCR	0x11				/* backspace */
#define MTC_SKFR	0x13				/* space file rev */
#define MTC_CLR		0x20				/* clear */
#define MTC_RD		0x21				/* read */
#define MTC_WR		0x22				/* write */
#define MTC_SKFF	0x23				/* space file fwd */
#define MTC_WEOF	0x30				/* write eof */
#define MTC_REW		0x38				/* rewind */
#define MTC_MASK	0x3F
#define MTC_STOP1	0x40				/* stop, set EOM */
#define MTC_STOP2	0x80				/* stop, set NMTN */

/* Status byte, * = in UST */

#define STA_ERR		0x80				/* error */
#define STA_EOF		0x40				/* end of file */
#define STA_EOT		0x20				/* *end of tape */
#define STA_NMTN	0x10				/* *no motion */
#define STA_UFLGS	(STA_EOT|STA_NMTN)		/* unit flags */
#define STA_MASK	(STA_ERR|STA_EOF|STA_BSY|STA_EOM)
#define SET_EX		(STA_ERR|STA_EOF|STA_NMTN)

extern uint32 int_req[INTSZ], int_enb[INTSZ];

uint8 mtxb[MT_MAXFR];					/* xfer buffer */
uint32 mt_bptr = 0;					/* pointer */
uint32 mt_blnt = 0;					/* length */
uint32 mt_sta = 0;					/* status byte */
uint32 mt_db = 0;					/* data buffer */
uint32 mt_xfr = 0;					/* data xfr in prog */
uint32 mt_arm[MT_NUMDR] = { 0 };			/* intr armed */
int32 mt_wtime = 10;					/* byte latency */
int32 mt_rtime = 1000;					/* record latency */
int32 mt_stopioe = 1;					/* stop on error */
uint8 mt_tplte[] = { 0, o_MT0, o_MT0*2, o_MT0*3, TPL_END };

static const uint8 bad_cmd[64] = {
 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1 };

DEVICE mt_dev;
uint32 mt (uint32 dev, uint32 op, uint32 dat);
t_bool mt_rdlntf (UNIT *uptr, t_mtrlnt *tbc, int32 *err);
t_bool mt_rdlntr (UNIT *uptr, t_mtrlnt *tbc, int32 *err);
t_bool mt_forwsp (UNIT *uptr, int32 *err);
t_bool mt_backsp (UNIT *uptr, int32 *err);
t_stat mt_svc (UNIT *uptr);
t_stat mt_reset (DEVICE *dptr);
t_stat mt_attach (UNIT *uptr, char *cptr);
t_stat mt_detach (UNIT *uptr);
t_stat mt_boot (int32 unitno, DEVICE *dptr);

/* MT data structures

   mt_dev	MT device descriptor
   mt_unit	MT unit list
   mt_reg	MT register list
   mt_mod	MT modifier list
*/

DIB mt_dib = { d_MT, 0, v_MT, mt_tplte, &mt, NULL };

UNIT mt_unit[] = {
	{ UDATA (&mt_svc, UNIT_ATTABLE + UNIT_DISABLE, 0) },
	{ UDATA (&mt_svc, UNIT_ATTABLE + UNIT_DISABLE, 0) },
	{ UDATA (&mt_svc, UNIT_ATTABLE + UNIT_DISABLE, 0) },
	{ UDATA (&mt_svc, UNIT_ATTABLE + UNIT_DISABLE, 0) }  };

REG mt_reg[] = {
	{ HRDATA (STA, mt_sta, 8) },
	{ HRDATA (BUF, mt_db, 8) },
	{ BRDATA (DBUF, mtxb, 16, 8, MT_MAXFR) },
	{ HRDATA (DBPTR, mt_bptr, 16) },
	{ HRDATA (DBLNT, mt_blnt, 17), REG_RO },
	{ FLDATA (XFR, mt_xfr, 0) },
	{ GRDATA (IREQ, int_req[l_MT], 16, MT_NUMDR, i_MT) },
	{ GRDATA (IENB, int_enb[l_MT], 16, MT_NUMDR, i_MT) },
	{ BRDATA (IARM, mt_arm, 16, 1, MT_NUMDR) },
	{ FLDATA (STOP_IOE, mt_stopioe, 0) },
	{ DRDATA (WTIME, mt_wtime, 24), PV_LEFT + REG_NZ },
	{ DRDATA (RTIME, mt_rtime, 24), PV_LEFT + REG_NZ },
	{ URDATA (UST, mt_unit[0].UST, 16, 8, 0, MT_NUMDR, 0) },
	{ URDATA (CMD, mt_unit[0].UCMD, 16, 8, 0, MT_NUMDR, 0) },
	{ URDATA (POS, mt_unit[0].pos, 10, 32, 0,
		  MT_NUMDR, PV_LEFT | REG_RO) },
	{ HRDATA (DEVNO, mt_dib.dno, 8), REG_HRO },
	{ HRDATA (SELCH, mt_dib.sch, 1), REG_HRO },
	{ NULL }  };

MTAB mt_mod[] = {
	{ UNIT_WLK, 0, "write enabled", "WRITEENABLED", NULL },
	{ UNIT_WLK, UNIT_WLK, "write locked", "LOCKED", NULL },
	{ MTAB_XTD|MTAB_VDV, 0, "DEVNO", "DEVNO",
		&set_dev, &show_dev, NULL },
	{ MTAB_XTD|MTAB_VDV, 0, "SELCH", "SELCH",
		&set_sch, &show_sch, NULL },
	{ 0 }  };

DEVICE mt_dev = {
	"MT", mt_unit, mt_reg, mt_mod,
	MT_NUMDR, 10, 31, 1, 16, 8,
	NULL, NULL, &mt_reset,
	&mt_boot, &mt_attach, &mt_detach,
	&mt_dib, DEV_DISABLE };

/* Magtape: IO routine */

uint32 mt (uint32 dev, uint32 op, uint32 dat)
{
uint32 i, f, t;
uint32 u = (dev - mt_dib.dno) / o_MT0;
UNIT *uptr = mt_dev.units + u;

switch (op) {						/* case IO op */
case IO_ADR:						/* select */
	sch_adr (mt_dib.sch, dev);			/* inform sel ch */
	return BY;					/* byte only */
case IO_RD:						/* read data */
	if (mt_xfr) mt_sta = mt_sta | STA_BSY;		/* xfr? set busy */
	return mt_db;					/* return data */
case IO_WD:						/* write data */
	if (mt_xfr) {					/* transfer? */
	    mt_sta = mt_sta | STA_BSY;			/* set busy */
	    if ((uptr->UCMD & (MTC_STOP1 | MTC_STOP2)) &&
	        ((uptr->UCMD & MTC_MASK) == MTC_WR))	/* while stopping? */
		mt_sta = mt_sta | STA_ERR;  }		/* write overrun */
	mt_db = dat & DMASK8;				/* store data */
	break;
case IO_SS:						/* status */
	mt_sta = mt_sta & STA_MASK;			/* ctrl status */
	if (uptr->flags & UNIT_ATT)			/* attached? */
	    t = mt_sta | (uptr->UST & STA_UFLGS);	/* yes, unit status */
	else t = mt_sta | STA_DU;			/* no, dev unavail */
	if (t & SET_EX) t = t | STA_EX;			/* test for ex */
	return t;
case IO_OC:						/* command */
	mt_arm[u] = int_chg (v_MT + u, dat, mt_arm[u]);
	f = dat & MTC_MASK;				/* get cmd */
	if (f == MTC_CLR) {				/* clear? */
	    mt_reset (&mt_dev);				/* reset world */
	    break;  }
	if (((uptr->flags & UNIT_ATT) == 0) ||		/* ignore if unatt */
	    bad_cmd[f] ||				/* or bad cmd */
	   (((f == MTC_WR) || (f == MTC_WEOF)) &&	/* or write */
	    (uptr->flags & UNIT_WPRT))) break;		/* and protected */
	for (i = 0; i < MT_NUMDR; i++) {		/* check other drvs */
	    if (sim_is_active (&mt_unit[i]) &&		/* active? */
		(mt_unit[i].UCMD != MTC_REW)) {		/* not rewind? */
		sim_cancel (&mt_unit[i]);		/* stop */
		mt_unit[i].UCMD = 0;  }
	if (sim_is_active (uptr) &&			/* unit active? */
	   !(uptr->UCMD & (MTC_STOP1 | MTC_STOP2)))	/* not stopping? */
		break;					/* ignore */
	if ((f == MTC_WR) || (f == MTC_REW)) mt_sta = 0;/* write, rew: bsy=0 */
	else mt_sta = STA_BSY;				/* bsy=1,nmtn,eom,err=0 */
	mt_bptr = mt_blnt = 0;				/* not yet started */
	if ((f == MTC_RD) || (f == MTC_WR))		/* data xfr? */
	    mt_xfr =  1;				/* set xfr flag */
	else mt_xfr = 0;  }
	uptr->UCMD = f;					/* save cmd */
	uptr->UST = 0;					/* clr tape stat */
	sim_activate (uptr, mt_rtime);			/* start op */
	break;  }
return 0;
}

/* Unit service

   A given operation can generate up to three interrupts

   - EOF generates an interrupt when set (read, space, wreof)
     BUSY will still be set, EOM and NMTN will be clear
   - After operation complete + delay, EOM generates an interrupt
     BUSY will be clear, EOM will be set, NMTN will be clear
   - After a further delay, NMTN generates an interrupt
     BUSY will be clear, EOM and NMTN will be set

   Rewind generates an interrupt when NMTN sets
*/

t_stat mt_svc (UNIT *uptr)
{
uint32 i, pnu;
int32 err;
int32 u = uptr - mt_dev.units;
uint32 dev = mt_dib.dno + (u * o_MT0);
t_mtrlnt tbc;
static t_mtrlnt bceof = { 0 };

err = 0;
pnu = MT_TST_PNU (uptr);				/* get pos not upd */
MT_CLR_PNU (uptr);					/* and clear */

if ((uptr->flags & UNIT_ATT) == 0) {			/* not attached? */
	uptr->UCMD = 0;					/* clr cmd */
	uptr->UST = 0;					/* set status */
	mt_xfr = 0;					/* clr op flags */
	mt_sta = STA_ERR | STA_EOM;			/* set status */
	if (mt_arm[u]) SET_INT (v_MT + u);		/* interrupt */
	return IORETURN (mt_stopioe, SCPE_UNATT);  }

if (uptr->UCMD & MTC_STOP2) {				/* stop, gen NMTN? */
	uptr->UCMD = 0;					/* clr cmd */
	uptr->UST = STA_NMTN;				/* set nmtn, not eot */
	mt_xfr = 0;					/* clr xfr */
	if (mt_arm[u]) SET_INT (v_MT + u);		/* set intr */
	return SCPE_OK;  }

if (uptr->UCMD & MTC_STOP1) {				/* stop, gen EOM? */
	uptr->UCMD = uptr->UCMD | MTC_STOP2;		/* clr cmd */
	mt_sta = (mt_sta & ~STA_BSY) | STA_EOM;		/* clr busy, set eom */
	if (mt_arm[u]) SET_INT (v_MT + u);		/* set intr */
	sim_activate (uptr, mt_rtime);			/* schedule */
	return SCPE_OK;  }				/* end case */

switch (uptr->UCMD) {					/* case on function */

case MTC_REW:						/* rewind */
	uptr->UCMD = 0;					/* clr cmd */
	uptr->pos = 0;					/* update position */
	uptr->UST = STA_NMTN | STA_EOT;			/* update status */
	mt_sta = mt_sta & ~STA_BSY;			/* don't set EOM */
	if (mt_arm[u]) SET_INT (v_MT + u);		/* interrupt */
	return SCPE_OK;

/* Unit service, continued

   For read, busy = 1 => buffer empty
   For write, busy = 1 => buffer full
   For read, data transfers continue for the full length of the
	record, or the maximum size of the transfer buffer
   For write, data transfers continue until a write is attempted
	and the buffer is empty
*/

case MTC_RD:						/* read */
	if (mt_blnt == 0) {				/* first time? */
	    if (mt_rdlntf (uptr, &tbc, &err)) break;	/* read rec lnt, err? */
	    mt_blnt = tbc;				/* set buf lnt */
	    if (tbc > MT_MAXFR) return SCPE_MTRLNT;	/* record too long? */
	    i = fxread (mtxb, sizeof (uint8), mt_blnt, uptr->fileref);
	    if (err = ferror (uptr->fileref)) {		/* error? */
		MT_SET_PNU (uptr);			/* pos not upd */
		break;  }
	    for ( ; i < mt_blnt; i++) mtxb[i] = 0;	/* fill with 0's */
	    uptr->pos = uptr->pos + ((tbc + 1) & ~1)	/* upd pos */
		+ (2 * sizeof (t_mtrlnt));  }

	if (sch_actv (mt_dib.sch, dev)) {		/* sch active? */
	    i = sch_wrmem (mt_dib.sch, mtxb, mt_blnt);	/* store rec in mem */
	    if (sch_actv (mt_dib.sch, dev))		/* sch still active? */
		sch_stop (mt_dib.sch);			/* stop chan, long rd */
	    else if (i < mt_blnt)			/* process entire rec? */
		mt_sta = mt_sta | STA_ERR;  }		/* no, overrun error */
	else if (mt_bptr < mt_blnt) {			/* no, if !eor */
	    if (!(mt_sta & STA_BSY))			/* busy still clr? */
		mt_sta = mt_sta | STA_ERR;		/* read overrun */
	    mt_db = mtxb[mt_bptr++];			/* get next byte */
	    mt_sta = mt_sta & ~STA_BSY;			/* !busy = buf full */
	    if (mt_arm[u]) SET_INT (v_MT + u);		/* set intr */
	    sim_activate (uptr, mt_wtime);		/* reschedule */
	    return SCPE_OK;  }
	break;						/* record done */

case MTC_WR:						/* write */
	if (sch_actv (mt_dib.sch, dev)) {		/* sch active? */
	    mt_bptr = sch_rdmem (mt_dib.sch, mtxb, MT_MAXFR);	/* get rec */
	    if (sch_actv (mt_dib.sch, dev))		/* not done? */
		sch_stop (mt_dib.sch);  }		/* stop chan */
	else if (mt_sta & STA_BSY) {			/* no, if !eor */
	    if (mt_bptr < MT_MAXFR)			/* if room */
		mtxb[mt_bptr++] = mt_db;		/* store in buf */
	    mt_sta = mt_sta & ~STA_BSY;			/* !busy = buf emp */
	    if (mt_arm[u]) SET_INT (v_MT + u);		/* set intr */
	    sim_activate (uptr, mt_wtime);		/* reschedule */
	    return SCPE_OK;  }

	if (mt_bptr) {					/* any chars? */
	    int32 ebc = (mt_bptr + 1) & ~1;		/* force even */
	    fseek (uptr->fileref, uptr->pos, SEEK_SET);
	    fxwrite (&mt_bptr, sizeof (t_mtrlnt), 1, uptr->fileref);
	    fxwrite (mtxb, sizeof (uint8), ebc, uptr->fileref);
	    fxwrite (&mt_bptr, sizeof (t_mtrlnt), 1, uptr->fileref);
	    if (err = ferror (uptr->fileref)) MT_SET_PNU (uptr);
	    else uptr->pos = uptr->pos + ebc + (2 * sizeof (t_mtrlnt));  }
	break;						/* record done */

/* Unit service, continued */

case MTC_WEOF:						/* write eof */
	fseek (uptr->fileref, uptr->pos, SEEK_SET);	/* set pos */
	fxwrite (&bceof, sizeof (t_mtrlnt), 1, uptr->fileref);
	if (err = ferror (uptr->fileref)) MT_SET_PNU (uptr);
	else uptr->pos = uptr->pos + sizeof (t_mtrlnt);	/* update pos */
	mt_sta = mt_sta | STA_EOF;			/* set eof */
	if (mt_arm[u]) SET_INT (v_MT + u);		/* interrupt */
	break;

case MTC_SKFF:						/* skip file fwd */
	while (mt_forwsp (uptr, &err)) ;		/* spc until EOF/EOT */
	break;

case MTC_SKFR:						/* skip file rev */
	while (mt_backsp (uptr, &err)) ;		/* spc until EOF/BOT */
	break;

case MTC_SPCR:						/* backspace */
	if (!pnu) mt_backsp (uptr, &err);		/* if pos not upd */
	break;  }					/* end case */

if (err != 0) {						/* I/O error */
	mt_sta = mt_sta | STA_ERR;
	perror ("MT I/O error");
	clearerr (uptr->fileref);
	if (mt_stopioe) return SCPE_IOERR;  }
uptr->UCMD = uptr->UCMD | MTC_STOP1;			/* set stop stage 1 */
sim_activate (uptr, mt_rtime);				/* schedule */
return SCPE_OK;
}

/* Tape motion routines */

t_bool mt_rdlntf (UNIT *uptr, t_mtrlnt *tbc, int32 *err)
{
int32 u = uptr - mt_dev.units;

fseek (uptr->fileref, uptr->pos, SEEK_SET);		/* position */
fxread (tbc, sizeof (t_mtrlnt), 1, uptr->fileref);	/* get bc */
if ((*err = ferror (uptr->fileref)) ||			/* err or eom? */
    feof (uptr->fileref) || (*tbc == MTR_EOM)) {
	mt_sta = mt_sta | STA_ERR;			/* set err */
	MT_SET_PNU (uptr);				/* pos not upd */
	return TRUE;  }
if (*tbc == MTR_TMK) {					/* tape mark? */
	mt_sta = mt_sta | STA_EOF;			/* set eof */
	if (mt_arm[u]) SET_INT (v_MT + u);		/* set intr */
	uptr->pos = uptr->pos + sizeof (t_mtrlnt);	/* update pos */
	return TRUE;  }
*tbc = MTRL (*tbc);
return FALSE;
}

t_bool mt_rdlntr (UNIT *uptr, t_mtrlnt *tbc, int32 *err)
{
int32 u = uptr - mt_dev.units;

if (uptr->pos < sizeof (t_mtrlnt)) {			/* at bot? */
	uptr->UST = uptr->UST | STA_EOT;		/* set err */
	return TRUE;  }
fseek (uptr->fileref, uptr->pos - sizeof (t_mtrlnt), SEEK_SET);
fxread (tbc, sizeof (t_mtrlnt), 1, uptr->fileref);	/* get bc */
if ((*err = ferror (uptr->fileref)) ||			/* err or eof? */
    feof (uptr->fileref)) {
	mt_sta = mt_sta | STA_ERR;			/* set err */
	return TRUE;  }
if (*tbc == MTR_EOM) {					/* eom? */
	mt_sta = mt_sta | STA_ERR;			/* set err */
	uptr->pos = uptr->pos - sizeof (t_mtrlnt);	/* update pos */
	return TRUE;  }
if (*tbc == MTR_TMK) {					/* tape mark? */
	mt_sta = mt_sta | STA_EOF;			/* set eof */
	if (mt_arm[u]) SET_INT (v_MT + u);		/* set intr */
	uptr->pos = uptr->pos - sizeof (t_mtrlnt);	/* update pos */
	return TRUE;  }
*tbc = MTRL (*tbc);
return FALSE;
}

t_bool mt_forwsp (UNIT *uptr, int32 *err)
{
t_mtrlnt tbc;

if (mt_rdlntf (uptr, &tbc, err)) return FALSE;		/* read rec lnt, err? */
uptr->pos = uptr->pos + ((tbc + 1) & ~1) +		/* space to next rec */
	(2 * sizeof (t_mtrlnt));
return TRUE;
}

t_bool mt_backsp (UNIT *uptr, int32 *err)
{
t_mtrlnt tbc;

if (mt_rdlntr (uptr, &tbc, err)) return FALSE;		/* read rec lnt, err? */
uptr->pos = uptr->pos - ((tbc + 1) & ~1) -		/* space to prv rec */
	(2 * sizeof (t_mtrlnt));
return TRUE;
}

/* Reset routine */

t_stat mt_reset (DEVICE *dptr)
{
uint32 u;
UNIT *uptr;

mt_bptr = mt_blnt = 0;					/* clr buf */
mt_sta = STA_BSY;					/* clr flags */
mt_xfr = 0;						/* clr controls */
for (u = 0; u < MT_NUMDR; u++) {			/* loop thru units */
	CLR_INT (v_MT + u);				/* clear int */
	CLR_ENB (v_MT + u);				/* disable int */
	mt_arm[u] = 0;					/* disarm int */
	uptr = mt_dev.units + u;
	MT_CLR_PNU (uptr);				/* clear pos flag */
	sim_cancel (uptr);				/* cancel activity */
	uptr->UST = (uptr->UST & STA_UFLGS) | STA_NMTN;	/* init status */
	uptr->UCMD = 0;  }				/* init cmd */
return SCPE_OK;
}

/* Attach routine */

t_stat mt_attach (UNIT *uptr, char *cptr)
{
int32 u = uptr - mt_dev.units;
t_stat r;

r = attach_unit (uptr, cptr);
if (r != SCPE_OK) return r;
uptr->pos = 0;
MT_CLR_PNU (uptr);
uptr->UST = STA_EOT;
if (mt_arm[u]) SET_INT (v_MT + u);
return r;
}

/* Detach routine */

t_stat mt_detach (UNIT* uptr)
{
int32 u = uptr - mt_dev.units;
t_stat r;

if ((uptr->flags & UNIT_ATT) == 0) return SCPE_OK;
r = detach_unit (uptr);
if (r != SCPE_OK) return r;
if (mt_arm[u]) SET_INT (v_MT + u);
MT_CLR_PNU (uptr);
uptr->UST = 0;
return SCPE_OK;
}

/* Bootstrap routine */

#define BOOT_START	0x50
#define BOOT_LEN	(sizeof (boot_rom) / sizeof (uint8))

static uint8 boot_rom[] = {
	0xD5, 0x00,		/* ST:	AL CF */
	0x00, 0xCF,
	0x43, 0x00,		/*	BR 80 */
	0x00, 0x80
};

t_stat mt_boot (int32 unitno, DEVICE *dptr)
{
extern uint32 PC, dec_flgs;
extern uint16 decrom[];
extern DIB sch_dib;
uint32 sch_dev;

if (decrom[0xD5] & dec_flgs) return SCPE_NOFNC;		/* AL defined? */
mt_unit[unitno].pos = 0;				/* rewind */
sch_dev = sch_dib.dno + mt_dib.sch;			/* sch dev # */
IOWriteBlk (BOOT_START, BOOT_LEN, boot_rom);		/* copy boot */
IOWriteB (AL_DEV, mt_dib.dno + (unitno * o_MT0));	/* set dev no for unit */
IOWriteB (AL_IOC, 0xA1);				/* set dev cmd */
IOWriteB (AL_SCH, sch_dev);				/* set dev no for chan */
PC = BOOT_START;
return SCPE_OK;
}