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/* hp2100_pif.c: HP 12620A/12936A privileged interrupt fence simulator
Copyright (c) 2008-2016, J. David Bryan
Permission is hereby granted, free of charge, to any person obtaining a
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PIF 12620A/12936A privileged interrupt fence
13-May-16 JDB Modified for revised SCP API function parameter types
10-Feb-12 JDB Deprecated DEVNO in favor of SC
28-Mar-11 JDB Tidied up signal handling
26-Oct-10 JDB Changed I/O signal handler for revised signal model
26-Jun-08 JDB Rewrote device I/O to model backplane signals
18-Jun-08 JDB Created PIF device
References:
- 12620A Breadboard Interface Kit Operating and Service Manual
(12620-90001, May-1978)
- 12936A Privileged Interrupt Fence Accessory Installation and Service Manual
(12936-90001, Mar-1974)
The Privileged Interupt Fence (PIF) was used in DOS and RTE systems to
provide privileged interrupt capability. In non-privileged systems, DOS and
RTE vectored all interrupts though the Central Interrupt Control (CIC)
routine. Within CIC, the interrupt system was turned off, the interrupt was
categorized, the associated driver was identified and mapped into logical
memory (if necessary), and the driver entered to handle the device service.
When the driver exited, the interrupt system was turned on before returning
to the point of interruption in the user's program. In addition, the DOS and
RTE operating systems themselves executed with the interrupt system off, as
they were not reentrant.
This process proved too lengthy for certain devices, which would lose
interrupts or be forced to limit I/O speeds as a result. To allow faster
service, a driver could be written as a "privileged" driver and generated
into a privileged system. A privileged system operated with the interrupt
system on when handling unprivileged device interrupts or executing within
the operating system. The PIF card was installed in the I/O backplane to
separate privileged from unprivileged devices by controlling the interrupt
priority chain signal (PRL) to lower-priority devices. The privileged cards
located below the fence were allowed to interrupt the service routines of the
unprivileged cards that were located above the fence.
When an unprivileged device interrupted, CIC would be entered as usual, and
the interrupt system would be turned off. However, after the system state
was saved, the PIF would be configured to break the priority chain (deny
PRL), so that subsequent interrupts from all unprivileged devices would be
deferred. Then the interrupt system would be turned on before normal CIC
processing continued. Interrupts from additional unprivileged devices would
be held off by the PIF until the driver completed and CIC returned, just as
in a non-privileged system.
However, if a privileged device interrupted, the interrupt would be allowed,
because the interrupt system was on, and the priority chain was intact for
the devices below the fence. A privileged device bypassed CIC and entered
the associated device driver directly, and this would occur even if an
unprivileged device driver or the operating system itself were executing.
This provided very fast interrupt service time.
HP produced two PIF cards: the 12936A Privileged Interrupt Fence Accessory
for DOS, and the 12620A Breadboard Interface for RTE. They behaved quite
differently and were not interchangeable.
The 12620A had the standard control and flag circuitry. It behaved as most
cards did; setting control and flag together lowered PRL and generated an
interrupt. The control and flag flip-flops were set and cleared with STC/CLC
and STF/CLF instructions. The SFS/SFC instructions could be used to test the
flag state.
The 12936A had a unique behavior. Setting either control or flag lowered
PRL. An interrupt occurred when flag was set and control was clear. The
control flip-flop was controlled with STC/CLC. The flag flip-flop was set
with OTA/B and cleared with CLF. SFC and SFS were not implemented and never
skipped.
*/
#include "hp2100_defs.h"
/* Device flags */
#define DEV_V_12936 (DEV_V_UF + 0) /* 12936A card */
#define DEV_12936 (1 << DEV_V_12936)
/* PIF state variables */
struct {
FLIP_FLOP control; /* control flip-flop */
FLIP_FLOP flag; /* flag flip-flop */
FLIP_FLOP flagbuf; /* flag buffer flip-flop */
} pif = { CLEAR, CLEAR, CLEAR };
/* PIF global routines */
IOHANDLER pif_io;
t_stat pif_reset (DEVICE *dptr);
t_stat pif_set_card (UNIT *uptr, int32 val, CONST char *cptr, void *desc);
t_stat pif_show_card (FILE *st, UNIT *uptr, int32 val, CONST void *desc);
/* PIF data structures.
pif_dib PIF device information block
pif_unit PIF unit list
pif_reg PIF register list
pif_mod PIF modifier list
pif_deb PIF debug list
pif_dev PIF device descriptor
Implementation note:
1. The SIMH developer's manual says that a device's unit list may be NULL.
However, if this is done, the register state cannot be examined or
altered via SCP. To work around this problem, we define a dummy unit
that is not used otherwise.
*/
DEVICE pif_dev;
DIB pif_dib = { &pif_io, PIF };
UNIT pif_unit = {
UDATA (NULL, 0, 0) /* dummy unit */
};
REG pif_reg [] = {
{ FLDATA (CTL, pif.control, 0) },
{ FLDATA (FLG, pif.flag, 0) },
{ FLDATA (FBF, pif.flagbuf, 0) },
{ ORDATA (SC, pif_dib.select_code, 6), REG_HRO },
{ ORDATA (DEVNO, pif_dib.select_code, 6), REG_HRO },
{ NULL }
};
MTAB pif_mod [] = {
{ MTAB_XTD | MTAB_VDV, 0, NULL, "12620A", &pif_set_card, NULL, NULL },
{ MTAB_XTD | MTAB_VDV, 1, NULL, "12936A", &pif_set_card, NULL, NULL },
{ MTAB_XTD | MTAB_VDV, 0, "TYPE", NULL, NULL, &pif_show_card, NULL },
{ MTAB_XTD | MTAB_VDV, 0, "SC", "SC", &hp_setsc, &hp_showsc, &pif_dev },
{ MTAB_XTD | MTAB_VDV | MTAB_NMO, 0, "DEVNO", "DEVNO", &hp_setdev, &hp_showdev, &pif_dev },
{ 0 }
};
DEVICE pif_dev = {
"PIF", /* device name */
&pif_unit, /* unit array */
pif_reg, /* register array */
pif_mod, /* modifier array */
1, /* number of units */
10, /* address radix */
31, /* address width */
1, /* address increment */
8, /* data radix */
8, /* data width */
NULL, /* examine routine */
NULL, /* deposit routine */
&pif_reset, /* reset routine */
NULL, /* boot routine */
NULL, /* attach routine */
NULL, /* detach routine */
&pif_dib, /* device information block */
DEV_DEBUG | DEV_DISABLE, /* device flags */
0, /* debug control flags */
NULL, /* debug flag name table */
NULL, /* memory size change routine */
NULL }; /* logical device name */
/* I/O signal handler.
Operation of the 12620A and the 12936A is different. The I/O responses of
the two cards are summarized below:
Signal 12620A Action 12936A Action
------ -------------------- --------------------
POPIO Set FBF, FLG Clear FBF, FLG
CRS Clear CTL Clear CTL
CLC Clear CTL Clear CTL
STC Set CTL Set CTL
CLF Clear FBF, FLG Clear FBF, FLG
STF Set FBF, FLG none
SFC Skip if FLG clear none
SFS Skip if FLG set none
IOI none none
IOO none Set FBF, FLG
PRL ~(CTL * FLG) ~(CTL + FLG)
IRQ CTL * FLG * FBF ~CTL * FLG * FBF
IAK Clear FBF Clear FBF
SRQ Follows FLG Not driven
Note that PRL and IRQ are non-standard for the 12936A.
*/
uint32 pif_io (DIB *dibptr, IOCYCLE signal_set, uint32 stat_data)
{
const char *hold_or_clear = (signal_set & ioCLF ? ",C" : "");
const t_bool is_rte_pif = (pif_dev.flags & DEV_12936) == 0;
IOSIGNAL signal;
IOCYCLE working_set = IOADDSIR (signal_set); /* add ioSIR if needed */
while (working_set) {
signal = IONEXT (working_set); /* isolate next signal */
switch (signal) { /* dispatch I/O signal */
case ioCLF: /* clear flag flip-flop */
pif.flag = pif.flagbuf = CLEAR; /* clear flag buffer and flag */
if (DEBUG_PRS (pif_dev))
fputs (">>PIF: [CLF] Flag cleared\n", sim_deb);
break;
case ioSTF: /* set flag flip-flop */
if (is_rte_pif) { /* RTE PIF? */
pif.flag = pif.flagbuf = SET; /* set flag buffer and flag */
if (DEBUG_PRS (pif_dev))
fputs (">>PIF: [STF] Flag set\n", sim_deb);
}
break;
case ioSFC: /* skip if flag is clear */
if (is_rte_pif) /* RTE PIF? */
setstdSKF (pif); /* card responds to SFC */
break;
case ioSFS: /* skip if flag is set */
if (is_rte_pif) /* RTE PIF? */
setstdSKF (pif); /* card responds to SFS */
break;
case ioIOO: /* I/O data output */
if (!is_rte_pif) { /* DOS PIF? */
pif.flag = pif.flagbuf = SET; /* set flag buffer and flag */
working_set = working_set | ioSIR; /* set SIR (not normally done for IOO) */
if (DEBUG_PRS (pif_dev))
fprintf (sim_deb, ">>PIF: [OTx%s] Flag set\n", hold_or_clear);
}
break;
case ioPOPIO: /* power-on preset to I/O */
pif.flag = pif.flagbuf = /* set or clear flag and flag buffer */
(is_rte_pif ? SET : CLEAR);
if (DEBUG_PRS (pif_dev))
fprintf (sim_deb, ">>PIF: [POPIO] Flag %s\n",
(is_rte_pif ? "set" : "cleared"));
break;
case ioCRS: /* control reset */
case ioCLC: /* clear control flip-flop */
pif.control = CLEAR; /* clear control */
if (DEBUG_PRS (pif_dev))
fprintf (sim_deb, ">>PIF: [%s%s] Control cleared\n",
(signal == ioCRS ? "CRS" : "CLC"), hold_or_clear);
break;
case ioSTC: /* set control flip-flop */
pif.control = SET; /* set control */
if (DEBUG_PRS (pif_dev))
fprintf (sim_deb, ">>PIF: [STC%s] Control set\n", hold_or_clear);
break;
case ioSIR: /* set interrupt request */
if (is_rte_pif) { /* RTE PIF? */
setstdPRL (pif); /* set standard PRL signal */
setstdIRQ (pif); /* set standard IRQ signal */
setstdSRQ (pif); /* set standard SRQ signal */
}
else { /* DOS PIF */
setPRL (dibptr->select_code, !(pif.control | pif.flag));
setIRQ (dibptr->select_code, !pif.control & pif.flag & pif.flagbuf);
}
if (DEBUG_PRS (pif_dev))
fprintf (sim_deb, ">>PIF: [SIR] PRL = %d, IRQ = %d\n",
PRL (dibptr->select_code),
IRQ (dibptr->select_code));
break;
case ioIAK: /* interrupt acknowledge */
pif.flagbuf = CLEAR;
break;
default: /* all other signals */
break; /* are ignored */
}
working_set = working_set & ~signal; /* remove current signal from set */
}
return stat_data;
}
/* Simulator reset routine */
t_stat pif_reset (DEVICE *dptr)
{
IOPRESET (&pif_dib); /* PRESET device (does not use PON) */
return SCPE_OK;
}
/* Set card type.
val == 0 --> set to 12936A (DOS PIF)
val == 1 --> set to 12620A (RTE PIF)
*/
t_stat pif_set_card (UNIT *uptr, int32 val, CONST char *cptr, void *desc)
{
if ((val < 0) || (val > 1) || (cptr != NULL)) /* sanity check */
return SCPE_ARG; /* bad argument */
if (val) /* DOS PIF selected? */
pif_dev.flags = pif_dev.flags | DEV_12936; /* set to 12936A */
else /* RTE PIF selected */
pif_dev.flags = pif_dev.flags & ~DEV_12936; /* set to 12620A */
return SCPE_OK;
}
/* Show card type */
t_stat pif_show_card (FILE *st, UNIT *uptr, int32 val, CONST void *desc)
{
if (pif_dev.flags & DEV_12936)
fputs ("12936A", st);
else
fputs ("12620A", st);
return SCPE_OK;
}