With this update, the erase gap operation has been split out of
"sim_tape_wrgap" into a separate, internal "tape_erase_fwd" routine that
is called from "sim_tape_wrgap" as well as from the new "sim_tape_errecf"
routine. There's a corresponding internal "tape_erase_rev" that's called
from the new "sim_tape_errecr" routine.
I've shimmed "sim_tape_rdlntf" and "sim_tape_rdlntr" to move the tape
context and debug stuff out of the routines that I'm maintaining. This
will allow me to replace those functions in their entirety with the
corresponding functions in my development sources for future updates.
It also allows me to keep Bob's version in sync. As my routines are static
and only called once from the shims, compilers should optimize away
the function calls and instead inline the code, so there'd be no extra call
overhead.
I'd also like to keep "tape_erase_fwd" and "tape_erase_rev" untouched for
the same reason. If you wish to add debug calls to "sim_tape_errecf" and
"sim_tape_errecr", that's fine.
Asynchronous clocks are now built for all simulators which are built with
SIM_ASYNCH_IO defined. The default behavior has asynchronous clocks
disabled since this is still experimental, but it can be enabled with
SET TIMER ASYNC.
Catchup clock ticks are now available, but since they're experimental,
they aren't enabled by default. Catchup ticks are only available if the
simulators clock device calls sim_rtcn_tick_ack to acknowledge processing
of clock ticks. The VAX simulators have been modified to leverage this.
Catchup clock ticks can be enabled with SET TIMER CATCHUP
Additionally, an idle threshold is provided which can be used to
influence when clock calibration may be suppressed. The default is not
to suppress calibration activities.
The various timer behaviors are visible with the SHOW TIMER command.
The state of the operating timer facilities is visible with: SHOW CLOCK
Timer events which are queued are visible with the SHOW QUEUE command.
Reworked all priority adjustment code to leverage a new
sim_os_set_thread_priority API which is coded to use pthreads or OS
priority adjustment APIs as necessary.
These changes facilitate more robust parameter type checking and helps
to identify unexpected coding errors.
Most simulators can now also be compiled with a C++ compiler without
warnings.
Additionally, these changes have also been configured to facilitate easier
backporting of simulator and device simulation modules to run under the
simh v3.9+ SCP framework.
If a TPC format tape image has garbage at the end of the image, but the
image contains multiple successive tape marks, then assume that logical
End Of Tape is immediately after the last successive tape marks.
OBSERVATION: Calling "sim_tape_rdrecf" to read a tape record sometimes
returns MTSE_EOM and sets the "position not updated" (PNU) flag, even when
an erase gap precedes the EOM. The correct response should be to return
MTSE_RUNAWAY to indicate that spacing over a gap did not end with a data
record or tape mark. Moreover, PNU should not be set, as the position has
been updated.
CAUSE: The routine attempts to handle this case by returning MTSE_RUNAWAY
if the EOF was detected while reading a buffer of gap markers. However, if
a buffer read ends immediately before an EOM marker or the physical EOF,
the next read attempt will return a zero buffer length. The routine
misinterprets this to mean that no gap was present and returns MTSE_EOM and
sets the PNU flag.
RESOLUTION: Modify "sim_tape_rdlntf" (sim_tape.c) to determine whether the
EOM marker or physical EOF was seen on the first or a subsequent buffer
read, and to return MTSE_EOM with PNU or MTSE_RUNAWAY without PNU,
respectively.
256. ENHANCEMENT: Add tape runaway support to the simulator tape library.
OBSERVATION: The ANSI specifications for NRZI, PE, and GCR tape recording
mandate a maximum length of 25 feet for erase gaps. Currently, an erase
gap of any length is ignored when reading or spacing. To allow detection
of non-compliant tape images, the simulator tape library is enhanced to
halt positioning and return tape runaway status if a gap of 25 feet or more
is encountered.
Runaway detection is enabled by calling the tape library to set the tape
density in bits per inch. If this call is not made, erase gaps present in
a tape image are effectively ignored. Also, with the addition of a
separate "set density" call, it is no longer necessary to supply the
density when writing erase gaps.
RESOLUTION: Modify "sim_tape_rdlntf" and "sim_tape_rdlntr" (sim_tape.c) to
detect tape runaway, and add a new MTSE_RUNAWAY status to sim_tape.h. Add
new "sim_tape_set_dens" and "sim_tape_show_dens" functions to set and show
the bits per inch for a unit, respectively, and eliminate the "bpi"
parameter to "sim_tape_wrgap" in preference to using the density
established by a previous "sim_tape_set_dens" call. Add named constants
to "sim_tape.h" that specify the density.
257. ENHANCEMENT: Improve performance when reading or spacing over erase gaps.
OBSERVATION: Performance when reading or spacing over erase gaps is poor,
especially in the reverse direction. Currently, each 4-byte gap marker is
read individually, and in the reverse direction, each read is preceded by a
seek to move the file pointer backward. This combination causes stream
cache invalidation and a physical disc access for each gap marker. As a
single gap consists of over 1000 markers, performance is far worse than if
a gap was read as a block.
RESOLUTION: Modify "sim_tape_rdlntf" and "sim_tape_rdlntr" (sim_tape.c) to
buffer reads of gap markers. Using a 128-element buffer, performance
improves about thirty-fold.
258. PROBLEM: Writing an end-of-medium positions the tape image after the mark.
OBSERVATION: The "sim_tape_wreom" simulator tape library function writes
an end-of-medium marker on the tape image. The intent is to erase the
remainder of the tape. The "SIMH Magtape Representation and Handling"
document states that the tape position is not updated by this function.
However, the function leaves the tape positioned after the marker.
A subsequent read would stop at the EOM marker. However, writing a new
marker over that one would then allow reading of the data following the EOM
that supposedly had been erased by the original "sim_tape_wreom" call.
CAUSE: The tape position is updated by the internal "sim_tape_wrdata" call
that is used to write the EOM marker, but it is not reset afterward by the
function.
RESOLUTION: Modify "sim_tape_wreom" (sim_tape.c) to reset the tape
position to point at the EOM marker before returning. This prevents
reading past an EOM marker, and a subsequent write will overwrite the
marker rather than embed it between data records.
259. PROBLEM: Reading through an erase gap in reverse may return EOM status.
OBSERVATION: A reverse read or spacing operation through an erase gap may
return end-of-medium status. Reading or spacing forward through the same
gap works properly.
CAUSE: Writing an erase gap over existing records may produce a gap that
is longer than requested. This occurs when truncating the last record to
be overlaid by the gap would leave a record that is shorter than the
minimum size allowed (eight bytes for the length words plus two bytes for
the data). In this case, the gap is lengthened to overlay the entire
record. If the new gap size is not evenly divisible by four, a half-gap is
metadata marker of value 0xFFFF added to the beginning of the gap.
If a gap that begins with a half-gap marker is written immediately after
a previous gap, the "seam" between gaps will contain the bytes FE FF FF FF
( FF FF ) FE FF FF FF.... Reading forward across this seam will yield a
metadata value of 0xFFFEFFFF, which is recognized and handled by seeking
two bytes back to resynchronize reading. However, reading in reverse will
yield the value 0xFFFFFFFF, which is interpreted as end-of-medium.
RESOLUTION: Modify "sim_tape_rdlntr" (sim_tape.c) to recognize 0xFFFFFFFF
as a half-gap marker and resynchronize in response. End of medium cannot
occur when reading in reverse, as it is impossible to position the tape
image beyond an EOM marker. Therefore, any 0xFFFFFFFF value encountered
must be a half-gap "seam" originating as above.
260. PROBLEM: sim_tape_wrgap fails when format is changed from SIMH format.
OBSERVATION: The HP 2100 magnetic tape simulator supports erase gaps and
calls sim_tape_wrgap when commanded to write a gap. However, if a tape
format other than SIMH format is selected, the call fails with MTSE_FMT.
CAUSE: Erase gaps are not supported in formats other than SIMH, but the
call should not fail. Instead, the call should be a "no-operation" if the
underlying format does not support gaps.
RESOLUTION: Modify "sim_tape_wrgap" (sim_tape.c) to return MTSE_OK with no
action performed if a tape format other than SIMH is selected.
261. PROBLEM: The magnetic tape format of an attached unit may be changed.
OBSERVATION: The magnetic tape library supports several tape image
formats. The format to use may be specified either by an "ATTACH -F"
command or by a "SET <unit> FORMAT" command. The latter calls the
"sim_tape_set_fmt" function, which allows the format of a file currently
attached to be changed. However, the format is an intrinsic property of
the tape image file, so changing it once the file has been attached makes
no sense.
CAUSE: Oversight.
RESOLUTION: Modify "sim_tape_set_fmt" (sim_tape.c) to return an error
(SCPE_ALATT, "Unit already attached") if the unit is attached.
- A -R flag is forced (attach READ ONLY) when TPC formatted tapes are attached. This should avoid updating file modified timestamps by any simh simulator.
- All write operations to TPC formatted tapes will fail with a write protected status.
The goals here being to simplify calling code while getting consistent output delivered everywhere it may be useful.
Modified most places which explicitly used sim_log or merely called printf to now avoid doing that and merely call sim_printf().
- Added event debug support to scp and the vax simulator
- Moved external declarations into include files related to modules which define them and removed random externs from modules which referenced them
- Fixed typos in sim_ether
- Fixed sim_disk and sim_tape to properly manage asynchronous threads on an i/o flush
