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/* pdp8_mt.c: PDP-8 magnetic tape simulator
Copyright (c) 1993-2011, 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 TM8E/TU10 magtape
16-Feb-06 RMS Added tape capacity checking
16-Aug-05 RMS Fixed C++ declaration and cast problems
18-Mar-05 RMS Added attached test to detach routine
25-Apr-03 RMS Revised for extended file support
29-Mar-03 RMS Added multiformat support
04-Mar-03 RMS Fixed bug in SKTR
01-Mar-03 RMS Fixed interrupt handling
Revised for magtape library
30-Oct-02 RMS Revised BOT handling, added error record handling
04-Oct-02 RMS Added DIBs, device number support
30-Aug-02 RMS Revamped error handling
28-Aug-02 RMS Added end of medium support
30-May-02 RMS Widened POS to 32b
22-Apr-02 RMS Added maximum record length test
06-Jan-02 RMS Changed enable/disable support
30-Nov-01 RMS Added read only unit, extended SET/SHOW support
24-Nov-01 RMS Changed UST, POS, FLG to arrays
25-Apr-01 RMS Added device enable/disable support
04-Oct-98 RMS V2.4 magtape format
22-Jan-97 RMS V2.3 magtape format
01-Jan-96 RMS Rewritten from TM8-E Maintenance Manual
Magnetic tapes are represented as a series of variable 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 "pdp8_defs.h"
#include "sim_tape.h"
#define MT_NUMDR 8 /* #drives */
#define USTAT u3 /* unit status */
#define MT_MAXFR (1 << 16) /* max record lnt */
#define WC_SIZE (1 << 12) /* max word count */
#define WC_MASK (WC_SIZE - 1)
/* Command/unit - mt_cu */
#define CU_V_UNIT 9 /* unit */
#define CU_M_UNIT 07
#define CU_PARITY 00400 /* parity select */
#define CU_IEE 00200 /* error int enable */
#define CU_IED 00100 /* done int enable */
#define CU_V_EMA 3 /* ext mem address */
#define CU_M_EMA 07
#define CU_EMA (CU_M_EMA << CU_V_EMA)
#define CU_DTY 00002 /* drive type */
#define CU_UNPAK 00001 /* 6b vs 8b mode */
#define GET_UNIT(x) (((x) >> CU_V_UNIT) & CU_M_UNIT)
#define GET_EMA(x) (((x) & CU_EMA) << (12 - CU_V_EMA))
/* Function - mt_fn */
#define FN_V_FNC 9 /* function */
#define FN_M_FNC 07
#define FN_UNLOAD 00
#define FN_REWIND 01
#define FN_READ 02
#define FN_CMPARE 03
#define FN_WRITE 04
#define FN_WREOF 05
#define FN_SPACEF 06
#define FN_SPACER 07
#define FN_ERASE 00400 /* erase */
#define FN_CRC 00200 /* read CRC */
#define FN_GO 00100 /* go */
#define FN_INC 00040 /* incr mode */
#define FN_RMASK 07700 /* readable bits */
#define GET_FNC(x) (((x) >> FN_V_FNC) & FN_M_FNC)
/* Status - stored in mt_sta or (*) uptr->USTAT */
#define STA_ERR (04000 << 12) /* error */
#define STA_REW (02000 << 12) /* *rewinding */
#define STA_BOT (01000 << 12) /* *start of tape */
#define STA_REM (00400 << 12) /* *offline */
#define STA_PAR (00200 << 12) /* parity error */
#define STA_EOF (00100 << 12) /* *end of file */
#define STA_RLE (00040 << 12) /* rec lnt error */
#define STA_DLT (00020 << 12) /* data late */
#define STA_EOT (00010 << 12) /* *end of tape */
#define STA_WLK (00004 << 12) /* *write locked */
#define STA_CPE (00002 << 12) /* compare error */
#define STA_ILL (00001 << 12) /* illegal */
#define STA_9TK 00040 /* 9 track */
/* #define STA_BAD 00020 *//* bad tape?? */
#define STA_INC 00010 /* increment error */
#define STA_LAT 00004 /* lateral par error */
#define STA_CRC 00002 /* CRC error */
#define STA_LON 00001 /* long par error */
#define STA_CLR (FN_RMASK | 00020) /* always clear */
#define STA_DYN (STA_REW | STA_BOT | STA_REM | STA_EOF | \
STA_EOT | STA_WLK) /* kept in USTAT */
extern uint16 M[];
extern int32 int_req, stop_inst;
extern UNIT cpu_unit;
int32 mt_cu = 0; /* command/unit */
int32 mt_fn = 0; /* function */
int32 mt_ca = 0; /* current address */
int32 mt_wc = 0; /* word count */
int32 mt_sta = 0; /* status register */
int32 mt_db = 0; /* data buffer */
int32 mt_done = 0; /* mag tape flag */
int32 mt_time = 10; /* record latency */
int32 mt_stopioe = 1; /* stop on error */
uint8 *mtxb = NULL; /* transfer buffer */
DEVICE mt_dev;
int32 mt70 (int32 IR, int32 AC);
int32 mt71 (int32 IR, int32 AC);
int32 mt72 (int32 IR, int32 AC);
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);
int32 mt_updcsta (UNIT *uptr);
int32 mt_ixma (int32 xma);
t_stat mt_map_err (UNIT *uptr, t_stat st);
t_stat mt_vlock (UNIT *uptr, int32 val, char *cptr, void *desc);
UNIT *mt_busy (void);
void mt_set_done (void);
/* 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 = { DEV_MT, 3, { &mt70, &mt71, &mt72 } };
UNIT mt_unit[] = {
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) },
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) },
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) },
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) },
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) },
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) },
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) },
{ UDATA (&mt_svc, UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE, 0) }
};
REG mt_reg[] = {
{ ORDATA (CMD, mt_cu, 12) },
{ ORDATA (FNC, mt_fn, 12) },
{ ORDATA (CA, mt_ca, 12) },
{ ORDATA (WC, mt_wc, 12) },
{ ORDATA (DB, mt_db, 12) },
{ GRDATA (STA, mt_sta, 8, 12, 12) },
{ ORDATA (STA2, mt_sta, 6) },
{ FLDATA (DONE, mt_done, 0) },
{ FLDATA (INT, int_req, INT_V_MT) },
{ FLDATA (STOP_IOE, mt_stopioe, 0) },
{ DRDATA (TIME, mt_time, 24), PV_LEFT },
{ URDATA (UST, mt_unit[0].USTAT, 8, 16, 0, MT_NUMDR, 0) },
{ URDATA (POS, mt_unit[0].pos, 10, T_ADDR_W, 0,
MT_NUMDR, PV_LEFT | REG_RO) },
{ FLDATA (DEVNUM, mt_dib.dev, 6), REG_HRO },
{ NULL }
};
MTAB mt_mod[] = {
{ MTUF_WLK, 0, "write enabled", "WRITEENABLED", &mt_vlock },
{ MTUF_WLK, MTUF_WLK, "write locked", "LOCKED", &mt_vlock },
{ MTAB_XTD|MTAB_VUN, 0, "FORMAT", "FORMAT",
&sim_tape_set_fmt, &sim_tape_show_fmt, NULL },
{ MTAB_XTD|MTAB_VUN, 0, "CAPACITY", "CAPACITY",
&sim_tape_set_capac, &sim_tape_show_capac, NULL },
{ MTAB_XTD|MTAB_VDV, 0, "DEVNO", "DEVNO",
&set_dev, &show_dev, NULL },
{ 0 }
};
DEVICE mt_dev = {
"MT", mt_unit, mt_reg, mt_mod,
MT_NUMDR, 10, 31, 1, 8, 8,
NULL, NULL, &mt_reset,
NULL, &mt_attach, &mt_detach,
&mt_dib, DEV_DISABLE | DEV_TAPE
};
/* IOT routines */
int32 mt70 (int32 IR, int32 AC)
{
int32 f;
UNIT *uptr;
uptr = mt_dev.units + GET_UNIT (mt_cu); /* get unit */
switch (IR & 07) { /* decode IR<9:11> */
case 1: /* LWCR */
mt_wc = AC; /* load word count */
return 0;
case 2: /* CWCR */
mt_wc = 0; /* clear word count */
return AC;
case 3: /* LCAR */
mt_ca = AC; /* load mem address */
return 0;
case 4: /* CCAR */
mt_ca = 0; /* clear mem address */
return AC;
case 5: /* LCMR */
if (mt_busy ()) /* busy? illegal op */
mt_sta = mt_sta | STA_ILL | STA_ERR;
mt_cu = AC; /* load command reg */
mt_updcsta (mt_dev.units + GET_UNIT (mt_cu));
return 0;
case 6: /* LFGR */
if (mt_busy ()) /* busy? illegal op */
mt_sta = mt_sta | STA_ILL | STA_ERR;
mt_fn = AC; /* load function */
if ((mt_fn & FN_GO) == 0) { /* go set? */
mt_updcsta (uptr); /* update status */
return 0;
}
f = GET_FNC (mt_fn); /* get function */
if (((uptr->flags & UNIT_ATT) == 0) ||
sim_is_active (uptr) ||
(((f == FN_WRITE) || (f == FN_WREOF)) && sim_tape_wrp (uptr))
|| (((f == FN_SPACER) || (f == FN_REWIND)) && sim_tape_bot (uptr))) {
mt_sta = mt_sta | STA_ILL | STA_ERR; /* illegal op error */
mt_set_done (); /* set done */
mt_updcsta (uptr); /* update status */
return 0;
}
uptr->USTAT = uptr->USTAT & STA_WLK; /* clear status */
if (f == FN_UNLOAD) { /* unload? */
detach_unit (uptr); /* set offline */
uptr->USTAT = STA_REW | STA_REM; /* rewinding, off */
mt_set_done (); /* set done */
}
else if (f == FN_REWIND) { /* rewind */
uptr->USTAT = uptr->USTAT | STA_REW; /* rewinding */
mt_set_done (); /* set done */
}
else mt_done = 0; /* clear done */
mt_updcsta (uptr); /* update status */
sim_activate (uptr, mt_time); /* start io */
return 0;
case 7: /* LDBR */
if (mt_busy ()) /* busy? illegal op */
mt_sta = mt_sta | STA_ILL | STA_ERR;
mt_db = AC; /* load buffer */
mt_set_done (); /* set done */
mt_updcsta (uptr); /* update status */
return 0;
} /* end switch */
return (stop_inst << IOT_V_REASON) + AC; /* ill inst */
}
int32 mt71 (int32 IR, int32 AC)
{
UNIT *uptr;
uptr = mt_dev.units + GET_UNIT (mt_cu);
switch (IR & 07) { /* decode IR<9:11> */
case 1: /* RWCR */
return mt_wc; /* read word count */
case 2: /* CLT */
mt_reset (&mt_dev); /* reset everything */
return AC;
case 3: /* RCAR */
return mt_ca; /* read mem address */
case 4: /* RMSR */
return ((mt_updcsta (uptr) >> 12) & 07777); /* read status */
case 5: /* RCMR */
return mt_cu; /* read command */
case 6: /* RFSR */
return (((mt_fn & FN_RMASK) | (mt_updcsta (uptr) & ~FN_RMASK))
& 07777); /* read function */
case 7: /* RDBR */
return mt_db; /* read data buffer */
}
return (stop_inst << IOT_V_REASON) + AC; /* ill inst */
}
int32 mt72 (int32 IR, int32 AC)
{
UNIT *uptr;
uptr = mt_dev.units + GET_UNIT (mt_cu); /* get unit */
switch (IR & 07) { /* decode IR<9:11> */
case 1: /* SKEF */
return (mt_sta & STA_ERR)? IOT_SKP + AC: AC;
case 2: /* SKCB */
return (!mt_busy ())? IOT_SKP + AC: AC;
case 3: /* SKJD */
return mt_done? IOT_SKP + AC: AC;
case 4: /* SKTR */
return (!sim_is_active (uptr) &&
(uptr->flags & UNIT_ATT))? IOT_SKP + AC: AC;
case 5: /* CLF */
if (!sim_is_active (uptr)) mt_reset (&mt_dev); /* if TUR, zap */
else { /* just ctrl zap */
mt_sta = 0; /* clear status */
mt_done = 0; /* clear done */
mt_updcsta (uptr); /* update status */
}
return AC;
} /* end switch */
return (stop_inst << IOT_V_REASON) + AC; /* ill inst */
}
/* Unit service
If rewind done, reposition to start of tape, set status
else, do operation, set done, interrupt
*/
t_stat mt_svc (UNIT *uptr)
{
int32 f, i, p, u, wc, xma;
t_mtrlnt tbc, cbc;
t_bool passed_eot;
uint16 c, c1, c2;
t_stat st, r = SCPE_OK;
u = (int32) (uptr - mt_dev.units); /* get unit number */
f = GET_FNC (mt_fn); /* get command */
xma = GET_EMA (mt_cu) + mt_ca; /* get mem addr */
wc = WC_SIZE - mt_wc; /* get wc */
if (uptr->USTAT & STA_REW) { /* rewind? */
sim_tape_rewind (uptr); /* update position */
if (uptr->flags & UNIT_ATT) /* still on line? */
uptr->USTAT = (uptr->USTAT & STA_WLK) | STA_BOT;
else uptr->USTAT = STA_REM;
if (u == GET_UNIT (mt_cu)) { /* selected? */
mt_set_done (); /* set done */
mt_updcsta (uptr); /* update status */
}
return SCPE_OK;
}
if ((uptr->flags & UNIT_ATT) == 0) { /* if not attached */
uptr->USTAT = STA_REM; /* unit off line */
mt_sta = mt_sta | STA_ILL | STA_ERR; /* illegal operation */
mt_set_done (); /* set done */
mt_updcsta (uptr); /* update status */
return IORETURN (mt_stopioe, SCPE_UNATT);
}
passed_eot = sim_tape_eot (uptr); /* passed eot? */
switch (f) { /* case on function */
case FN_READ: /* read */
case FN_CMPARE: /* read/compare */
st = sim_tape_rdrecf (uptr, mtxb, &tbc, MT_MAXFR); /* read rec */
if (st == MTSE_RECE) /* rec in err? */
mt_sta = mt_sta | STA_PAR | STA_ERR;
else if (st != MTSE_OK) { /* other error? */
r = mt_map_err (uptr, st); /* map error */
mt_sta = mt_sta | STA_RLE | STA_ERR; /* err, eof/eom, tmk */
break;
}
cbc = (mt_cu & CU_UNPAK)? wc: wc * 2; /* expected bc */
if (tbc != cbc) /* wrong size? */
mt_sta = mt_sta | STA_RLE | STA_ERR;
if (tbc < cbc) { /* record small? */
cbc = tbc; /* use smaller */
wc = (mt_cu & CU_UNPAK)? cbc: (cbc + 1) / 2;
}
for (i = p = 0; i < wc; i++) { /* copy buffer */
xma = mt_ixma (xma); /* increment xma */
mt_wc = (mt_wc + 1) & 07777; /* incr word cnt */
if (mt_cu & CU_UNPAK) c = mtxb[p++];
else {
c1 = mtxb[p++] & 077;
c2 = mtxb[p++] & 077;
c = (c1 << 6) | c2;
}
if ((f == FN_READ) && MEM_ADDR_OK (xma))
M[xma] = c;
else if ((f == FN_CMPARE) && (M[xma] != c)) {
mt_sta = mt_sta | STA_CPE | STA_ERR;
break;
}
}
break;
case FN_WRITE: /* write */
tbc = (mt_cu & CU_UNPAK)? wc: wc * 2;
for (i = p = 0; i < wc; i++) { /* copy buf to tape */
xma = mt_ixma (xma); /* incr mem addr */
if (mt_cu & CU_UNPAK)
mtxb[p++] = M[xma] & 0377;
else {
mtxb[p++] = (M[xma] >> 6) & 077;
mtxb[p++] = M[xma] & 077;
}
}
if ((st = sim_tape_wrrecf (uptr, mtxb, tbc))) { /* write rec, err? */
r = mt_map_err (uptr, st); /* map error */
xma = GET_EMA (mt_cu) + mt_ca; /* restore xma */
}
else mt_wc = 0; /* ok, clear wc */
break;
case FN_WREOF:
if ((st = sim_tape_wrtmk (uptr))) /* write tmk, err? */
r = mt_map_err (uptr, st); /* map error */
break;
case FN_SPACEF: /* space forward */
do {
mt_wc = (mt_wc + 1) & 07777; /* incr wc */
if ((st = sim_tape_sprecf (uptr, &tbc))) { /* space rec fwd, err? */
r = mt_map_err (uptr, st); /* map error */
break; /* stop */
}
} while ((mt_wc != 0) && (passed_eot || !sim_tape_eot (uptr)));
break;
case FN_SPACER: /* space reverse */
do {
mt_wc = (mt_wc + 1) & 07777; /* incr wc */
if ((st = sim_tape_sprecr (uptr, &tbc))) { /* space rec rev, err? */
r = mt_map_err (uptr, st); /* map error */
break; /* stop */
}
} while (mt_wc != 0);
break;
} /* end case */
if (!passed_eot && sim_tape_eot (uptr)) /* just passed EOT? */
uptr->USTAT = uptr->USTAT | STA_EOT;
mt_cu = (mt_cu & ~CU_EMA) | ((xma >> (12 - CU_V_EMA)) & CU_EMA);
mt_ca = xma & 07777; /* update mem addr */
mt_set_done (); /* set done */
mt_updcsta (uptr); /* update status */
return r;
}
/* Update controller status */
int32 mt_updcsta (UNIT *uptr)
{
mt_sta = (mt_sta & ~(STA_DYN | STA_CLR)) | (uptr->USTAT & STA_DYN);
if (((mt_sta & STA_ERR) && (mt_cu & CU_IEE)) ||
(mt_done && (mt_cu & CU_IED)))
int_req = int_req | INT_MT;
else int_req = int_req & ~INT_MT;
return mt_sta;
}
/* Test if controller busy */
UNIT *mt_busy (void)
{
int32 u;
UNIT *uptr;
for (u = 0; u < MT_NUMDR; u++) { /* loop thru units */
uptr = mt_dev.units + u;
if (sim_is_active (uptr) && ((uptr->USTAT & STA_REW) == 0))
return uptr;
}
return NULL;
}
/* Increment extended memory address */
int32 mt_ixma (int32 xma) /* incr extended ma */
{
int32 v;
v = ((xma + 1) & 07777) | (xma & 070000); /* wrapped incr */
if (mt_fn & FN_INC) { /* increment mode? */
if (xma == 077777) /* at limit? error */
mt_sta = mt_sta | STA_INC | STA_ERR;
else v = xma + 1; /* else 15b incr */
}
return v;
}
/* Set done */
void mt_set_done (void)
{
mt_done = 1; /* set done */
mt_fn = mt_fn & ~(FN_CRC | FN_GO | FN_INC); /* clear func<4:6> */
return;
}
/* Map tape error status */
t_stat mt_map_err (UNIT *uptr, t_stat st)
{
switch (st) {
case MTSE_FMT: /* illegal fmt */
case MTSE_UNATT: /* unattached */
mt_sta = mt_sta | STA_ILL | STA_ERR;
case MTSE_OK: /* no error */
return SCPE_IERR; /* never get here! */
case MTSE_TMK: /* end of file */
uptr->USTAT = uptr->USTAT | STA_EOF; /* set EOF */
mt_sta = mt_sta | STA_ERR;
break;
case MTSE_IOERR: /* IO error */
mt_sta = mt_sta | STA_PAR | STA_ERR; /* set par err */
if (mt_stopioe)
return SCPE_IOERR;
break;
case MTSE_INVRL: /* invalid rec lnt */
mt_sta = mt_sta | STA_PAR | STA_ERR; /* set par err */
return SCPE_MTRLNT;
case MTSE_RECE: /* record in error */
case MTSE_EOM: /* end of medium */
mt_sta = mt_sta | STA_PAR | STA_ERR; /* set par err */
break;
case MTSE_BOT: /* reverse into BOT */
uptr->USTAT = uptr->USTAT | STA_BOT; /* set status */
mt_sta = mt_sta | STA_ERR;
break;
case MTSE_WRP: /* write protect */
mt_sta = mt_sta | STA_ILL | STA_ERR; /* illegal operation */
break;
}
return SCPE_OK;
}
/* Reset routine */
t_stat mt_reset (DEVICE *dptr)
{
int32 u;
UNIT *uptr;
mt_cu = mt_fn = mt_wc = mt_ca = mt_db = mt_sta = mt_done = 0;
int_req = int_req & ~INT_MT; /* clear interrupt */
for (u = 0; u < MT_NUMDR; u++) { /* loop thru units */
uptr = mt_dev.units + u;
sim_cancel (uptr); /* cancel activity */
sim_tape_reset (uptr); /* reset tape */
if (uptr->flags & UNIT_ATT) uptr->USTAT =
(sim_tape_bot (uptr)? STA_BOT: 0) |
(sim_tape_wrp (uptr)? STA_WLK: 0);
else uptr->USTAT = STA_REM;
}
if (mtxb == NULL)
mtxb = (uint8 *) calloc (MT_MAXFR, sizeof (uint8));
if (mtxb == NULL)
return SCPE_MEM;
return SCPE_OK;
}
/* Attach routine */
t_stat mt_attach (UNIT *uptr, char *cptr)
{
t_stat r;
int32 u = uptr - mt_dev.units; /* get unit number */
r = sim_tape_attach (uptr, cptr);
if (r != SCPE_OK)
return r;
uptr->USTAT = STA_BOT | (sim_tape_wrp (uptr)? STA_WLK: 0);
if (u == GET_UNIT (mt_cu))
mt_updcsta (uptr);
return r;
}
/* Detach routine */
t_stat mt_detach (UNIT* uptr)
{
int32 u = uptr - mt_dev.units; /* get unit number */
if (!(uptr->flags & UNIT_ATT)) /* check for attached */
return SCPE_OK;
if (!sim_is_active (uptr))
uptr->USTAT = STA_REM;
if (u == GET_UNIT (mt_cu))
mt_updcsta (uptr);
return sim_tape_detach (uptr);
}
/* Write lock/enable routine */
t_stat mt_vlock (UNIT *uptr, int32 val, char *cptr, void *desc)
{
int32 u = uptr - mt_dev.units; /* get unit number */
if ((uptr->flags & UNIT_ATT) && (val || sim_tape_wrp (uptr)))
uptr->USTAT = uptr->USTAT | STA_WLK;
else uptr->USTAT = uptr->USTAT & ~STA_WLK;
if (u == GET_UNIT (mt_cu))
mt_updcsta (uptr);
return SCPE_OK;
}