i1401_mt.c - emulators/simh - Rivoreo Source Code Repositories

 /* IBM 1401 magnetic tape simulator

    Copyright (c) 1993-1999, 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.

    14-Apr-99	RMS	Changed t_addr to unsigned
    04-Oct-98	RMS	V2.4 magtape format

    Magnetic tapes are represented as a series of variable 16b records
    of the form:

 	32b byte count
 	byte 0
 	byte 1
 	:
 	byte n-2
 	byte n-1
 	32b byte count

    If the byte count is odd, the record is padded with an extra byte
    of junk.  File marks are represented by a byte count of 0.
 */

 #include "i1401_defs.h"

 #define MT_NUMDR	7				/* #drives */
 #define UNIT_V_WLK	(UNIT_V_UF + 0)			/* write locked */
 #define UNIT_WLK	(1 << UNIT_V_WLK)
 #define UNIT_W_UF	2				/* #save flags */

 extern unsigned char M[];				/* memory */
 extern int32 ind[64];
 extern int32 BS, iochk;
 extern UNIT cpu_unit;
 unsigned int8 dbuf[MAXMEMSIZE * 2];			/* tape buffer */
 t_stat mt_reset (DEVICE *dptr);
 UNIT *get_unit (int32 unit);
 extern size_t fxread (void *bptr, size_t size, size_t count, FILE *fptr);
 extern size_t fxwrite (void *bptr, size_t size, size_t count, FILE *fptr);

 /* MT data structures

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

 UNIT mt_unit[] = {
 	{ UDATA (NULL, UNIT_DIS, 0) },			/* doesn't exist */
 	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
 	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
 	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
 	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
 	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
 	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) }  };

 REG mt_reg[] = {
 	{ FLDATA (END, ind[IN_END], 0) },
 	{ FLDATA (ERR, ind[IN_TAP], 0) },
 	{ FLDATA (PAR, ind[IN_PAR], 0) },
 	{ DRDATA (POS1, mt_unit[1].pos, 31), PV_LEFT + REG_RO },
 	{ DRDATA (POS2, mt_unit[2].pos, 31), PV_LEFT + REG_RO },
 	{ DRDATA (POS3, mt_unit[3].pos, 31), PV_LEFT + REG_RO },
 	{ DRDATA (POS4, mt_unit[4].pos, 31), PV_LEFT + REG_RO },
 	{ DRDATA (POS5, mt_unit[5].pos, 31), PV_LEFT + REG_RO },
 	{ DRDATA (POS6, mt_unit[6].pos, 31), PV_LEFT + REG_RO },
 	{ GRDATA (FLG1, mt_unit[1].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
 		  REG_HRO },
 	{ GRDATA (FLG2, mt_unit[2].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
 		  REG_HRO },
 	{ GRDATA (FLG3, mt_unit[3].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
 		  REG_HRO },
 	{ GRDATA (FLG4, mt_unit[4].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
 		  REG_HRO },
 	{ GRDATA (FLG5, mt_unit[5].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
 		  REG_HRO },
 	{ GRDATA (FLG6, mt_unit[6].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
 		  REG_HRO },
 	{ NULL }  };

 MTAB mt_mod[] = {
 	{ UNIT_WLK, 0, "write enabled", "ENABLED", NULL },
 	{ UNIT_WLK, UNIT_WLK, "write locked", "LOCKED", NULL },
 	{ 0 }  };

 DEVICE mt_dev = {
 	"MT", mt_unit, mt_reg, mt_mod,
 	MT_NUMDR, 10, 31, 1, 8, 6,
 	NULL, NULL, &mt_reset,
 	NULL, NULL, NULL };

 /* Function routine

    Inputs:
 	unit	=	unit character
 	mod	=	modifier character
    Outputs:
 	status	=	status
 */

 t_stat mt_func (int32 unit, int32 mod)
 {
 int32 err;
 t_mtrlnt tbc;
 UNIT *uptr;
 static t_mtrlnt bceof = { 0 };

 if ((uptr = get_unit (unit)) == NULL) return STOP_INVMTU; /* valid unit? */
 if ((uptr -> flags & UNIT_ATT) == 0) return SCPE_UNATT;	/* attached? */
 switch (mod) {						/* case on modifier */
 case BCD_B:						/* backspace */
 	ind[IN_END] = 0;				/* clear end of reel */
 	if (uptr -> pos == 0) return SCPE_OK;		/* at bot? */
 	fseek (uptr -> fileref, uptr -> pos - sizeof (t_mtrlnt),
 		SEEK_SET);
 	fxread (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
 	if ((err = ferror (uptr -> fileref)) ||
 	    (feof (uptr -> fileref))) break;
 	if (tbc == 0)				/* file mark? */
 		uptr -> pos = uptr -> pos - sizeof (t_mtrlnt);
 	else uptr -> pos = uptr -> pos - ((MTRL (tbc) + 1) & ~1) -
 		(2 * sizeof (t_mtrlnt));
 	break;  					/* end case */
 case BCD_E:						/* erase = nop */
 	if (uptr -> flags & UNIT_WLK) return STOP_MTL;
 	return SCPE_OK;
 case BCD_M:						/* write tapemark */
 	if (uptr -> flags & UNIT_WLK) return STOP_MTL;
 	fseek (uptr -> fileref, uptr -> pos, SEEK_SET);
 	fxwrite (&bceof, sizeof (t_mtrlnt), 1, uptr -> fileref);
 	err = ferror (uptr -> fileref);
 	uptr -> pos = uptr -> pos + sizeof (t_mtrlnt);
 	break;
 case BCD_R:						/* rewind */
 	uptr -> pos = 0;				/* update position */
 	return SCPE_OK;
 case BCD_U:						/* unload */
 	uptr -> pos = 0;				/* update position */
 	return detach_unit (uptr);			/* detach */
 default:
 	return STOP_INVM;  }
 if (err != 0) {						/* I/O error */
 	perror ("MT I/O error");
 	clearerr (uptr -> fileref);
 	if (iochk) return SCPE_IOERR;
 	ind[IN_TAP] = 1;  }
 return SCPE_OK;
 }

 /* Read and write routines

    Inputs:
 	unit	=	unit character
 	flag	=	normal, word mark, or binary mode
 	mod	=	modifier character
    Outputs:
 	status	=	status
 */

 t_stat mt_io (int32 unit, int32 flag, int32 mod)
 {
 int32 err, i, t, wm_seen;
 t_mtrlnt tbc;
 UNIT *uptr;

 if ((uptr = get_unit (unit)) == NULL) return STOP_INVMTU; /* valid unit? */
 if ((uptr -> flags & UNIT_ATT) == 0) return SCPE_UNATT;	/* attached? */
 switch (mod) {
 case BCD_R:						/* read */
 	ind[IN_TAP] = ind[IN_END] = 0;			/* clear error */
 	wm_seen = 0;					/* no word mk seen */
 	fseek (uptr -> fileref, uptr -> pos, SEEK_SET);
 	fxread (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
 	if ((err = ferror (uptr -> fileref)) || (feof (uptr -> fileref))) {
 		ind[IN_END] = 1;			/* err or eof? */
 		break;  }
 	if (tbc == 0) {					/* tape mark? */
 		ind[IN_END] = 1;			/* set end mark */
 		uptr -> pos = uptr -> pos + sizeof (t_mtrlnt);
 		break;  }
 	tbc = MTRL (tbc);				/* ignore error flag */
 	i = fxread (dbuf, sizeof (int8), tbc, uptr -> fileref);
 	for ( ; i < tbc; i++) dbuf[i] = 0;		/* fill with 0's */
 	err = ferror (uptr -> fileref);
 	uptr -> pos = uptr -> pos + ((tbc + 1) & ~1) +
 		(2 * sizeof (t_mtrlnt));
 	for (i = 0; (i < tbc) && (M[BS] != (BCD_GRPMRK + WM)); i++) {
 		t = dbuf[i];				/* get char */
 		if ((flag != MD_BIN) && (t == BCD_ALT)) t = BCD_BLANK;
 		if (flag == MD_WM) {			/* word mk mode? */
 			if ((t == BCD_WM) && (wm_seen == 0)) wm_seen = WM;
 			else {	M[BS] = wm_seen | (t & CHAR);
 				wm_seen = 0;  }  }
 		else M[BS] = (M[BS] & WM) | (t & CHAR);
 		if (!wm_seen) BS++;
 		if (ADDR_ERR (BS)) {
 			BS = BA | (BS % MAXMEMSIZE);
 			return STOP_NXM;  }  }
 	M[BS++] = BCD_GRPMRK + WM;			/* end of record */
 	break;

 case BCD_W:
 	if (uptr -> flags & UNIT_WLK) return STOP_MTL;	/* locked? */
 	if (M[BS] == (BCD_GRPMRK + WM)) return STOP_MTZ;	/* eor? */
 	ind[IN_TAP] = ind[IN_END] = 0;			/* clear error */
 	for (tbc = 0; (t = M[BS++]) != (BCD_GRPMRK + WM); ) {
 		if ((t & WM) && (flag == MD_WM)) dbuf[tbc++] = BCD_WM;
 		if (((t & CHAR) == BCD_BLANK) && (flag != MD_BIN))
 			dbuf[tbc++] = BCD_ALT;
 		else dbuf[tbc++] = t & CHAR;
 		if (ADDR_ERR (BS)) {
 			BS = BA | (BS % MAXMEMSIZE);
 			return STOP_NXM;  }  }
 	fseek (uptr -> fileref, uptr -> pos, SEEK_SET);
 	fxwrite (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
 	fxwrite (dbuf, sizeof (int8), (tbc + 1) & ~1, uptr -> fileref);
 	fxwrite (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
 	err = ferror (uptr -> fileref);
 	uptr -> pos = uptr -> pos + ((tbc + 1) & ~1) +
 		(2 * sizeof (t_mtrlnt));
 	break;
 default:
 	return STOP_INVM;  }

 if (err != 0) {						/* I/O error */
 	perror ("MT I/O error");
 	clearerr (uptr -> fileref);
 	if (iochk) return SCPE_IOERR;
 	ind[IN_TAP] = 1;  }				/* flag error */
 return SCPE_OK;
 }

 /* Get unit pointer from unit number */

 UNIT *get_unit (int32 unit)
 {
 if ((unit <= 0) || (unit >= MT_NUMDR)) return NULL;
 else return mt_dev.units + unit;
 }

 /* Reset routine */

 t_stat mt_reset (DEVICE *dptr)
 {
 ind[IN_END] = ind[IN_PAR] = ind[IN_TAP] = 0;		/* clear indicators */
 return SCPE_OK;
 }
	/* IBM 1401 magnetic tape simulator

	Copyright (c) 1993-1999, 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.

	14-Apr-99 RMS Changed t_addr to unsigned
	04-Oct-98 RMS V2.4 magtape format

	Magnetic tapes are represented as a series of variable 16b records
	of the form:

	32b byte count
	byte 0
	byte 1
	:
	byte n-2
	byte n-1
	32b byte count

	If the byte count is odd, the record is padded with an extra byte
	of junk. File marks are represented by a byte count of 0.
	*/

	#include "i1401_defs.h"

	#define MT_NUMDR 7 /* #drives */
	#define UNIT_V_WLK (UNIT_V_UF + 0) /* write locked */
	#define UNIT_WLK (1 << UNIT_V_WLK)
	#define UNIT_W_UF 2 /* #save flags */

	extern unsigned char M[]; /* memory */
	extern int32 ind[64];
	extern int32 BS, iochk;
	extern UNIT cpu_unit;
	unsigned int8 dbuf[MAXMEMSIZE * 2]; /* tape buffer */
	t_stat mt_reset (DEVICE *dptr);
	UNIT *get_unit (int32 unit);
	extern size_t fxread (void bptr, size_t size, size_t count, FILE fptr);
	extern size_t fxwrite (void bptr, size_t size, size_t count, FILE fptr);

	/* MT data structures

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

	UNIT mt_unit[] = {
	{ UDATA (NULL, UNIT_DIS, 0) }, /* doesn't exist */
	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) },
	{ UDATA (NULL, UNIT_DISABLE + UNIT_ATTABLE + UNIT_BCD, 0) } };

	REG mt_reg[] = {
	{ FLDATA (END, ind[IN_END], 0) },
	{ FLDATA (ERR, ind[IN_TAP], 0) },
	{ FLDATA (PAR, ind[IN_PAR], 0) },
	{ DRDATA (POS1, mt_unit[1].pos, 31), PV_LEFT + REG_RO },
	{ DRDATA (POS2, mt_unit[2].pos, 31), PV_LEFT + REG_RO },
	{ DRDATA (POS3, mt_unit[3].pos, 31), PV_LEFT + REG_RO },
	{ DRDATA (POS4, mt_unit[4].pos, 31), PV_LEFT + REG_RO },
	{ DRDATA (POS5, mt_unit[5].pos, 31), PV_LEFT + REG_RO },
	{ DRDATA (POS6, mt_unit[6].pos, 31), PV_LEFT + REG_RO },
	{ GRDATA (FLG1, mt_unit[1].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
	REG_HRO },
	{ GRDATA (FLG2, mt_unit[2].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
	REG_HRO },
	{ GRDATA (FLG3, mt_unit[3].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
	REG_HRO },
	{ GRDATA (FLG4, mt_unit[4].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
	REG_HRO },
	{ GRDATA (FLG5, mt_unit[5].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
	REG_HRO },
	{ GRDATA (FLG6, mt_unit[6].flags, 8, UNIT_W_UF, UNIT_V_UF - 1),
	REG_HRO },
	{ NULL } };

	MTAB mt_mod[] = {
	{ UNIT_WLK, 0, "write enabled", "ENABLED", NULL },
	{ UNIT_WLK, UNIT_WLK, "write locked", "LOCKED", NULL },
	{ 0 } };

	DEVICE mt_dev = {
	"MT", mt_unit, mt_reg, mt_mod,
	MT_NUMDR, 10, 31, 1, 8, 6,
	NULL, NULL, &mt_reset,
	NULL, NULL, NULL };

	/* Function routine

	Inputs:
	unit = unit character
	mod = modifier character
	Outputs:
	status = status
	*/

	t_stat mt_func (int32 unit, int32 mod)
	{
	int32 err;
	t_mtrlnt tbc;
	UNIT *uptr;
	static t_mtrlnt bceof = { 0 };

	if ((uptr = get_unit (unit)) == NULL) return STOP_INVMTU; /* valid unit? */
	if ((uptr -> flags & UNIT_ATT) == 0) return SCPE_UNATT; /* attached? */
	switch (mod) { /* case on modifier */
	case BCD_B: /* backspace */
	ind[IN_END] = 0; /* clear end of reel */
	if (uptr -> pos == 0) return SCPE_OK; /* at bot? */
	fseek (uptr -> fileref, uptr -> pos - sizeof (t_mtrlnt),
	SEEK_SET);
	fxread (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
	if ((err = ferror (uptr -> fileref)) \|\|
	(feof (uptr -> fileref))) break;
	if (tbc == 0) /* file mark? */
	uptr -> pos = uptr -> pos - sizeof (t_mtrlnt);
	else uptr -> pos = uptr -> pos - ((MTRL (tbc) + 1) & ~1) -
	(2 * sizeof (t_mtrlnt));
	break; /* end case */
	case BCD_E: /* erase = nop */
	if (uptr -> flags & UNIT_WLK) return STOP_MTL;
	return SCPE_OK;
	case BCD_M: /* write tapemark */
	if (uptr -> flags & UNIT_WLK) return STOP_MTL;
	fseek (uptr -> fileref, uptr -> pos, SEEK_SET);
	fxwrite (&bceof, sizeof (t_mtrlnt), 1, uptr -> fileref);
	err = ferror (uptr -> fileref);
	uptr -> pos = uptr -> pos + sizeof (t_mtrlnt);
	break;
	case BCD_R: /* rewind */
	uptr -> pos = 0; /* update position */
	return SCPE_OK;
	case BCD_U: /* unload */
	uptr -> pos = 0; /* update position */
	return detach_unit (uptr); /* detach */
	default:
	return STOP_INVM; }
	if (err != 0) { /* I/O error */
	perror ("MT I/O error");
	clearerr (uptr -> fileref);
	if (iochk) return SCPE_IOERR;
	ind[IN_TAP] = 1; }
	return SCPE_OK;
	}

	/* Read and write routines

	Inputs:
	unit = unit character
	flag = normal, word mark, or binary mode
	mod = modifier character
	Outputs:
	status = status
	*/

	t_stat mt_io (int32 unit, int32 flag, int32 mod)
	{
	int32 err, i, t, wm_seen;
	t_mtrlnt tbc;
	UNIT *uptr;

	if ((uptr = get_unit (unit)) == NULL) return STOP_INVMTU; /* valid unit? */
	if ((uptr -> flags & UNIT_ATT) == 0) return SCPE_UNATT; /* attached? */
	switch (mod) {
	case BCD_R: /* read */
	ind[IN_TAP] = ind[IN_END] = 0; /* clear error */
	wm_seen = 0; /* no word mk seen */
	fseek (uptr -> fileref, uptr -> pos, SEEK_SET);
	fxread (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
	if ((err = ferror (uptr -> fileref)) \|\| (feof (uptr -> fileref))) {
	ind[IN_END] = 1; /* err or eof? */
	break; }
	if (tbc == 0) { /* tape mark? */
	ind[IN_END] = 1; /* set end mark */
	uptr -> pos = uptr -> pos + sizeof (t_mtrlnt);
	break; }
	tbc = MTRL (tbc); /* ignore error flag */
	i = fxread (dbuf, sizeof (int8), tbc, uptr -> fileref);
	for ( ; i < tbc; i++) dbuf[i] = 0; /* fill with 0's */
	err = ferror (uptr -> fileref);
	uptr -> pos = uptr -> pos + ((tbc + 1) & ~1) +
	(2 * sizeof (t_mtrlnt));
	for (i = 0; (i < tbc) && (M[BS] != (BCD_GRPMRK + WM)); i++) {
	t = dbuf[i]; /* get char */
	if ((flag != MD_BIN) && (t == BCD_ALT)) t = BCD_BLANK;
	if (flag == MD_WM) { /* word mk mode? */
	if ((t == BCD_WM) && (wm_seen == 0)) wm_seen = WM;
	else { M[BS] = wm_seen \| (t & CHAR);
	wm_seen = 0; } }
	else M[BS] = (M[BS] & WM) \| (t & CHAR);
	if (!wm_seen) BS++;
	if (ADDR_ERR (BS)) {
	BS = BA \| (BS % MAXMEMSIZE);
	return STOP_NXM; } }
	M[BS++] = BCD_GRPMRK + WM; /* end of record */
	break;

	case BCD_W:
	if (uptr -> flags & UNIT_WLK) return STOP_MTL; /* locked? */
	if (M[BS] == (BCD_GRPMRK + WM)) return STOP_MTZ; /* eor? */
	ind[IN_TAP] = ind[IN_END] = 0; /* clear error */
	for (tbc = 0; (t = M[BS++]) != (BCD_GRPMRK + WM); ) {
	if ((t & WM) && (flag == MD_WM)) dbuf[tbc++] = BCD_WM;
	if (((t & CHAR) == BCD_BLANK) && (flag != MD_BIN))
	dbuf[tbc++] = BCD_ALT;
	else dbuf[tbc++] = t & CHAR;
	if (ADDR_ERR (BS)) {
	BS = BA \| (BS % MAXMEMSIZE);
	return STOP_NXM; } }
	fseek (uptr -> fileref, uptr -> pos, SEEK_SET);
	fxwrite (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
	fxwrite (dbuf, sizeof (int8), (tbc + 1) & ~1, uptr -> fileref);
	fxwrite (&tbc, sizeof (t_mtrlnt), 1, uptr -> fileref);
	err = ferror (uptr -> fileref);
	uptr -> pos = uptr -> pos + ((tbc + 1) & ~1) +
	(2 * sizeof (t_mtrlnt));
	break;
	default:
	return STOP_INVM; }

	if (err != 0) { /* I/O error */
	perror ("MT I/O error");
	clearerr (uptr -> fileref);
	if (iochk) return SCPE_IOERR;
	ind[IN_TAP] = 1; } /* flag error */
	return SCPE_OK;
	}

	/* Get unit pointer from unit number */

	UNIT *get_unit (int32 unit)
	{
	if ((unit <= 0) \|\| (unit >= MT_NUMDR)) return NULL;
	else return mt_dev.units + unit;
	}

	/* Reset routine */

	t_stat mt_reset (DEVICE *dptr)
	{
	ind[IN_END] = ind[IN_PAR] = ind[IN_TAP] = 0; /* clear indicators */
	return SCPE_OK;
	}