PiDP-8/I Software

os8-run: A Scripting Language for Driving OS/8
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History and Motivation

In the beginning, the PiDP-8/I project shipped a hand-made and hand-maintained OS/8 disk image. This image had multiple problems, and sometimes the by-hand fixes to those problems caused other problems.

For the 2017.12.22 release, we created a tool called mkos8 which creates this disk programmatically based on the user's configuration choices. This has many virtues:

That process worked fine for the limited scope of problem it was meant to cover: creation of an OS/8 V3D RK05 image meant for use with SIMH's PDP-8 simulator, which was configured in a very particular way. It doesn't solve a number of related problems that should be simple extensions to the idea:

Shortly after release 2017.12.22 came out, Bill Cattey began work on os8-run to solve these problems. This new tool implements a scripting language and a lot of new underlying functionality so that we can not only implement all of what mkos8 did, we can now write scripts to do much more.

The goals of the project are:


os8-run is a general script running facility that can:

Key Implementation Detail: Pexpect

Under the covers, run-os8 is a Python script that uses the Python pexpect library to interact programmatically with SIMH and OS/8. In principle, there is no limit to the complexity of the dialogs we can script with this.

In practice, the major difficulty in constructing correct Pexpect scripts is that if you fall out of step with what is "expect"ed, the expect engine can get into a state where it is blocked waiting for input that either never will arrive or that already passed by and now can no longer be matched. To avoid blocking forever in such situations, os8-run configures Pexpect to time out eventually, resulting in a big ugly Python backtrace. The os8-run scripts that ship with the PiDP-8/I software distribution should never do this, but as you write your own, you may find yourself having to debug such problems.

Running os8-run with the -v option gives verbose output that enables you to watch every step of the script as it runs.


In the documentation below, we use the term "POSIX" to refer to the host side of the conversation or to resources available on that side. We use this generic term because the PiDP-8/I software runs on many different platforms, currently limited only to those that are either POSIX-compliant (e.g. macOS) or those sufficiently close (e.g. Linux). Thus, a "file from POSIX" refers to a file being copied from the host system running os8-run and SIMH's PDP-8 simulator into the simulated environment.

Very few script language commands fail fatally. The design principle was to ask, "Is the primary use case of this command a prerequisite for other work that would make no sense if this command failed?" If the answer is, "yes", then the failure of command kills the execution of the whole script and aborts os8-run. Commands that have fatal exits are mentioned specifically in the command reference section below.

Case Sensitivity -- a tricky issue

It is expected that scripts will be written on the POSIX platform with a case-sensitive text editor. os8-run should be considered case-sensitive as well. Scripts should specify the os8-run commands and options in lower case, and the OS/8 commands, options, and filenames in upper case.

POSIX is ostensibly a case-sensitive platform, filenames, commands and command arguments are always case sensitive. This was a basic design decision from the earliest days of ancestral Multics.

The OS/8 platform began as an upper-case only environment. Only late in the evolution of the PDP-8 as a word processing platform, did lower case even exist on OS/8. SIMH addresses this reality with two different console device setups, KSR and 7b.

In KSR mode, typed lower case characters are upcased automatically before being sent to the running system.

In 7b mode, all characters are passed to OS/8 without case conversion.

The current OS/8 default OS/8 system image run with this software distribution is called v3d.rk05. It is configured to be as modern as possible. It contains patches to force lower case characters typed to the Keyboard Monitor to upper case so they will be understood. A patch is made to OS/8 BASIC to do the same thing. However many programs available for use under OS/8 are upper case only, and get confused unless you set CAPS LOCK on your keyboard.

All of the example scripts specify OS/8 commands in upper case. Such commands could have been specified in lower case, and would work just fine if run in the default v3d.rk05 system image. However, since a basic use case of os8-run is to be able to run scripts against arbitrary system images (which probably will not have patches to deal with lower case), use of lower case for OS/8 commands, arguments, or filenames is discouraged.

os8-run does not get involved with forcing OS/8 commands or filenames to upper case if they appear as lower case in scripts. os8-run does offer commands to toggle the SIMH console support between KSR and 7b. See the configure command.

Although the os8-run commands and options could have been made case insensitive, and the OS/8 commands, options, and filenames could have been forced to upper case, rendering them case insensitive, there would still be that aspect where the script developer would have to deal with establishing case-sensitive POSIX filename conventions that would fit with OS/8's upper case only filenames. The decision was made to have the scripting language require, mindfulness of case, where the developer adopts a discipline to use lower case for scripting commands, and upper case when dealing with OS/8.

Apologies in advance for the inconvenience of having to do that. Time will tell if it was or was not the right decision to have been made.

An Illustrative First Example

Here are some example os8-run scripts:

Example 1: Begin work on a new RK05 image that gets an updated version of the OS/8 BUILD utility from POSIX source. (Perhaps it was found on the net.)

mount rk0 $bin/v3d.rk05 required
mount rk1 $bin/os8-v3f-build.rk05 preserve

cpto $src/os8/v3f/BUILD.PA RKA1:BUILD.PA /A

boot rk0


begin cdprog SYS:ABSLDR.SV
end cdprog SYS:ABSLDR.SV


The above script does the following:

POSIX Path Expansions

Notice in the above example the use of the variables $bin/ and $src/ in the POSIX path specifications. These refer to particular directories which vary depending on whether you run this script from the PiDP-8/I source tree or from the installation tree. Not only does using these variables allow the same script to work in both trees, it allows your script to run regardless of where those source and installation trees are on any given system.

The scheme works much like predefined POSIX shell variables, but the underlying mechanism is currently very limited. First, the substitution can only occur at the very beginning of a POSIX file specification. Second, the only values currently defined are:

$build/ The absolute path to the root of the build.
$src/ The absolute path to the root of the source.
$bin/ The directory where executables and runable image files are installed at build time
$media/ The absolute path to OS/8 media files
$os8mi/ The absolute path to OS/8 media files used as input at build time
$os8mo/ The absolute path to OS/8 media files produced as output at build time

To add new values, modify .../lib/pidp8i/ and rebuild the PiDP-8/I software. Beware that changing this generates the file, which is a very deep dependency. Touching this file will cause all the OS/8 bootable system image files to be rebuilt, which can take quite some time even on a fast host computer.

Execution Contexts

It is important to be mindful of the different command contexts when running scripts under os8-run:

Examples of begin / end blocks:

The commands that execute in the OS/8 environment require a system image to be attached and booted. Attempts to run OS/8 commands without having booted OS/8 kill the script.

Scripting commands such as mount, umount, and configure execute in the SIMH context. OS/8 is suspended for these commands.

Ideally we would just resume OS/8 with a SIMH continue command when we are finished running SIMH commands. Unfortunately this does not work under Python expect. The expect engine needs a command prompt.

Although hitting the erase character (RUBOUT) or the line kill character (CTRL/U) to a terminal-connected SIMH OS/8 session gives a command prompt, these actions don't work under Python expect. We don't know why.

Booting OS/8 gives a fresh prompt.

Restarting the OS/8 Monitor with a SIMH command line of "go 7600" works.

The least disruptive way we have found to resume OS/8 under Python expect after having escaped to SIMH is to issue the SIMH continue command, then pause for an keyboard delay, then send CTRL/C then pause again, then send \r\n. That wakes OS/8 back up and produces a Keyboard Monitor prompt.

The code that underlies all this keeps track of the switch between the SIMH and OS/8 contexts. However it does not presume to do this resumption because the CTRL/C will quit out of any program being run under OS/8, and return to the keyboard monitor level.

Because os8-run creates the begin / end blocks with their own interpreter loops, around commands with complex command structures, it guarantees that the switch into SIMH context will only happen when OS/8 is quiescent in the Keyboard Monitor.

Although os8-run provides a resume command that can appear in scripts after the commands that escape out to SIMH, using it is optional. os8-run checks the context and issues its own resume call if needed.


os8-run [-h] [-d] [-v] [-vv] [--enable enable_option] ... [--disable disable_option] ... script-file ...

Positional Arguments
script-file One or more script files to run
Optional Arguments
-h show this help message and exit
-d add extra debugging output, normally suppressed
-v verbose script status output instead of the usual few progress messages
-vv very verbose: Includes SIMH expect output with the verbose output.
Known Enable Options
focal69 Add FOCAL69 to the built OS/8 RK05 image
music Add *.MU files to the built OS/8 RK05 image
vtedit Add the TECO VTEDIT setup to the built OS/8 RK05 image
Known Disable Options
ba Leave *.BA BASIC games and demos off the built OS/8 RK05 image
uwfocal Leave U/W FOCAL (only) off the built OS/8 RK05 image
macrel Leave the MACREL assembler off the built OS/8 RK05 image
dcp Leave the DCP disassembler off the built OS/8 RK05 image
k12 Leave 12-bit Kermit off the built OS/8 RK05 image
cc8 Leave the native OS/8 CC8 compiler off the built OS/8 RK05 image
crt Leave CRT-style rubout processing off the built OS/8 RK05 image
advent Leave Adventure off the built OS/8 RK05 image
fortran-ii Leave FORTRAN II off the built OS/8 RK05 image
fortran-iv Leave FORTRAN IV off the built OS/8 RK05 image
init Leave the OS/8 INIT message off the built OS/8 RK05 image
chess Leave the CHECKMO-II game of chess off the built OS/8 RK05 image
lcmod Disable the OS/8 command upcasing patch. Used when SIMH has tti ksr set.

Script Language Command Inventory

Here is a list of the os8-run scripting language commands in alphabetical order.

boot Boot the named SIMH device.
begin Begin complex conditional or sub-command block.
configure Perform specific SIMH configuration activities.
copy Make a copy of a POSIX file.
cpfrom Copy from OS/8 into a file in POSIX environment.
cpto Copy POSIX file to OS/8 environment.
disable Set disablement of a feature by keyword.
enable Set enablement of a feature by keyword.
end End complex conditional or sub-command block.
exit Exit os8-run and send status
include Execute a subordinate script file.
mount Mount an image file as a SIMH attached device.
[ocomp](#ocomp-com Run the OS/8 Octal Compare Utility.
os8 Run arbitrary OS/8 command.
pal8 Run OS/8 PAL8 assembler.
patch Run a patch file.
print Print information from running script.
resume Resume OS/8 at Keyboard Monitor command level.
restart Restart OS/8.
umount Unmount a SIMH attached device image.

These commands are described in subsections of Script Language Command Reference below. That section presents commands in an order appropriate to building up an understanding of making first simple and then complex scripts with os8-run.

Script Language Command Reference

print - Print information from a running script.

print output

The simplest script command is print which allows display of status information from the running script. output is simply displayed. If the verbose option to os8-run is set, the line number of the print command is included in the output.

exit - Exit os8-run and send status.

exit [status]

The exit command allows immediate termination of the os8-run script.

The status argument is optional. If the argument is an integer, os8-run will return that status to the calling command shell. This enables rich signalling of status when os8-run itself is run as a script.

The status argument can also be a string. If a string is specified, the status returned by os8-run to the command shell is 1, and the string is printed on exit. (This is the default behavior of the python sys.exit() procedure.)

include — Execute a subordinate script file.

include script-file-path

The script file named in script-file-path is executed. If no fatal errors are encountered during that execution, then the main script continues on.

A fatal error in an included script kills the whole execution of os8-run.

mount — Mount an image file as a SIMH attached device.

mount simh-dev image-file [option ...]

Because the primary expectation with os8-run scripts is that image files are mounted, booted and operated on, the failure of a mount command is fatal.

mount Options

new If there is an existing file, rename it with a .save extension
because we want to create a new empty image file. If there is
already an existing .save version, the existing .save version is lost.
required image-file is required to exist, otherwise abort the script.
preserve If image-file already exists, create a copy with a version number suffix.
This is useful when you want to prevent overwrites of a good image file
with changes that might not work. os8-run preserves all versions seen
and creates new version that doesn't overwrite any of the previous ones.
readonly Passes the -r option to SIMH attach to mount the device in read only mode.
ro Abbreviation for readonly.
scratch Create a writeable scratch version of the named image file and mount it.
This is helpful when you are booting a distribution DECtape.
Booted DECtape images must be writeable. To protect a distribution DECtape,
use the scratch option. When all script runs are done, the scratch version
is deleted.

Note that the preserve and new options approach preservation in fundamentally different ways: preserve keeps all old copies, but new only keeps the most recent copy. This is because it is expected that the new option is used with the expectation that old content is not precious, but that we have a backstop. Whereas the expectation of the use of preserve is that any and all old versions are precious and should be left to a person explicitly to delete.

When new image files are created, some sort of initialization is necessary before files can be written to them. Although the new and preserve options could have performed an OS/8 ZERO command to initialize the directories, it was decided not to do so because in some cases, the OS/8 device drivers required to perform such actions might not be active until farther down in a complex script.

mount Examples

Mount the v3d.rk05 image, to be found in in the install directory for runable image files, which must exist, on SIMH rk0.

mount rk0 $bin/v3d.rk05 required

Mount the advent.tu56 image, to be found in the media input directory, which must exist, on SIMH dt1 in read only mode, which will protect it from inadvertent modification.

mount dt1 $os8mi/subsys/advent.tu56 readonly required

Create a new image file in the media output directory, and mount it on the SIMH dt0 device.

mount dt0 $os8mo/test_copy.tu56 new

Create a writeable copy of the distribution DECtape, al-4711c-ba-os8-v3d-1.1978.tu56, to be found in the media input directory, which must exist. Mount it on SIMH dt0 ready for for a read/write boot. Delete the copy when the script is done.

 mount dt0 $os8mi/al-4711c-ba-os8-v3d-1.1978.tu56 required scratch

Create a new image file system.tu56 in the install director for runable image files. If the file already exists, create a new version. If the numbered version file exists, keep incrementing the version number for the new file until a pre-existing file is not found.

For example, if system.tu56 was not found, the new file would be called system.tu56. If it was found the next version would be called system_1.tu56. If system_1.tu56 and system_2.tu56 were found the new file would be called system_3.tu56, and so on.

 mount dt0 $bin/system.tu56 preserve

The preserve option is helpful when experimenting with scripts that may not work the first time.

umount — Unmount a SIMH attached device image.

umount simh-device

This is just a wrapper for the SIMH detach command.

Here is the rationale for having added a umount command instead of just calling the detach command from SIMH by its own same name:

Starting from the idea of providing some abstract but useful actions to take around the SIMH attach command, the decision was made to lean on the POSIX mount command because people familiar with mount were used to hanging lots of different abstract but useful actions off of it.

umount was adopted as what people familiar with mount would expect as the command to undo what mount had done. This seemed preferable to inventing attach with more features as a wholly new syntactic/semantic design.

boot — Boot the named SIMH device.

boot simh-device

Boot OS/8 on the named simh-device and enter the OS/8 run-time context.

The boot command tests to see if something is attached to the SIMH being booted. If nothing is attached, the command fails with a fatal error.

This test does not protect against trying to boot an image lacking a system area and thus not bootable. This can't be tested in advance because booting a non-bootable image simply hangs the virtual machine. Heroic measures, like looking for magic system area bits in the image file were deemed too much work.

If an attempt is made to boot an image with no system area, os8-run hangs for a while and then gives a timeout backtrace.

resume — Resume OS/8 at Keyboard Monitor command level.


The least disruptive way to resume operations under SIMH is to issue the continue command. Although it took a while, we finally got this command working reliably. There were timing and workflow issues that had to be resolved.

The resume command checks to see if OS/8 has been booted and refuses to act if it has not.

restart — Restart OS/8.


Equivalent to the SIMH command line of "go 7600", but which confirms we got our Monitor prompt.

Before resume was developed, the next less disruptive way to get an OS/8 Keyboard Monitor prompt was to restart SIMH at address 07600. This is considered a soft-restart of OS/8. It is less disruptive than a boot command, because the boot command loads OS/8 into main memory from the boot device, whereas restarting at location 07600 is just a resart without a reload.

The restart command checks to see if OS/8 has been booted and refuses to act if it has not.

copy — Make a copy of a POSIX file.

copy source-path destination-path

The most common activity for os8-run is to modify a system image.

However, we often want to keep the original and modify a copy. For example, the PiDP-8/I software build system creates the default OS/8 RK05 disk image v3d.rk05, which in turn is a modified version of v3d-dist.rk05. We keep the latter around so we don't have to keep rebuilding the baseline.

Instead of requiring some external caller to carefully preserve the old file, the "make a copy with arbitrary name" functionality was added by way of this command.

Adding an option to mount was considered, but in the interests of allowing an arbitrary name for the modified image, a separate command was created.

cpto — Copy POSIX file to OS/8 environment.

cpto posix-path [option]

cpto posix-path os8-filespec [option]

The option is either empty or exactly one of

/A OS/8 PIP ASCII format. POSIX newlines are converted to OS/8 newlines.
/B OS/8 PIP BIN format. Paper tape leader/trailer may be added.
/I OS/8 PIP image format. Bit for Bit copy.

If no option is specified, /A is assumed.

IMPORTANT: Because we are parsing both OS/8 and POSIX file specifications, we can't just parse out the slash in the options. Options must be preceded with whitespace. Otherwise it would be mis-parsed as part of a file spec.

In the first form of the command, the OS/8 file specification is left out, and one is synthesized from the file component of the posix-path.

This is how you get files to OS/8 from the outside world. For example, this enables source code management using modern tools. The builder script would check out the latest source and use an os8-run script beginning with a cpto command to send it to OS/8 for assembly, linking, installation, etc.


Copy a POSIX file onto the default OS/8 device DSK: under the name INIT.CM:

 cpto ../media/os8/

cpfrom — Copy from OS/8 to a file in POSIX environment.

cpfromos8-filespec posix-path [option]

The option is either empty or exactly one of

/A OS/8 PIP ASCII format. POSIX newlines are converted to OS/8 newlines.
/B OS/8 PIP BIN format. Paper tape leader/trailer may be added.
/I OS/8 PIP image format. Bit for Bit copy.

If no option is specified, /A is assumed.

IMPORTANT: Because we are parsing both OS/8 and POSIX file specifications, we can't just parse out the slash in the options. Options must be preceded with whitespace. Otherwise it would be mis-parsed as part of a file spec.

Unlike cpto there is only one form of the command. Both the os8-filespec and the posix-path must be specified. The options are the same for both cpfrom and cpto.

Copy files from the running OS/8 environment to the POSIX environment running SIMH.


Copy a listing file into the current working directory of the executing os8-run:

cpfrom DSK:OS8.LS ./ /A

os8 — Run arbitrary OS/8 command.

os8 os8-command-line

Everything on the script command line after "os8 " is passed, uninterpreted, to the OS/8 keyboard monitor with the expectation that the command will return to the monitor command level and the command prompt, "." will be produced.

This command should be used ONLY for OS/8 commands that return immediately to command level. BATCH scripts do this, and they can be run from here.

The os8 command is aware of a special enablement keyword: transcript. (See the enable disable section below.) If transcript is enabled, the output from running the OS/8 command line is printed.

For example, if you wanted to display the contents of a DECtape image you are constructing but no other command lines fed to the os8 command you would do this:

enable transcript
os8 DIR DTA0:
disable transcript

This transcript capability provides a fine grained debugging aid.

pal8 — Run OS/8 PAL8 assembler.

Actually, the PAL8 assembler can be called just fine by using the os8 command, for example:


However, an separate pal8 command was created to enable richer display of errors.


Create a binary OS8.BN on partition B of rk05 drive 1 from OS8.PA source file found on partition A of rk05 drive 1.

pal8 RKB1:OS8.BN<RKA1:OS8.PA

Create a binary OS8.BN on partition B of rk05 drive 1 and a listing file OS8.LS on the default device DSK: from OS8.PA source file found on partition A of rk05 drive 1.


ocomp — Run OS/8 OCOMP Octal Compare and Dump Utility.

This command was added to allow file verification. It wraps a call to the OS/8 OCOMP utility with some expect parsing to recognize when two files are identical, or when one is missing.

A typical command line would look like this:

ocomp TTY:<DTA1:E8.SV,SYS:E8.SV

To confirm that the E8 executable on SYS: matches the one found on the image mounted on DTA1:

Note that, although one can use the full power of the OCOMP utility, the setup here in os8-run considers anything other than the "NOTHING OUTPUT" indicating identical files to be a "failure".

However, the transcript option is available so that octal dumps can be produced. For example, the script:

mount rk0 $bin/v3d.rk05 required scratch
boot rk0

enable transcript
ocomp TTY:<PS.C

produces the following output

$ bin/os8-run scripts/test/ocomp.os8 
Running script file: scripts/test/ocomp.os8
0000   ( ABSOLUTE BLOCK 2302 )
0000  5257 0252 7320 4762  5356 0364 7720 1741  7343 6341 5247 0363
0014  7364 4762 7341 3756  5354 0345 4252 6657  5212 5257 7240 7311
0030  7366 5757 7745 3640  7351 4364 6240 2656  5330 0305 6703 1303
0044  7240 7341 7344 2640  7356 2764 7762 2240  7750 1751 7240 4746
0060  7354 7345 5355 0345  4252 6657 4212 5215  5215 1612 7344 3345
0074  7351 2756 6240 7703  6725 2316 5640 2261  4215 6612 7212 4611
0110  5356 0364 6741 5762  6662 6660 5254 6351  4352 6673 4212 5215
0124  7751 2356 7240 0755  5351 4356 4251 5215  4373 5215 7211 7746
0140  5362 4240 5751 0675  5673 6351 6703 2717  5716 5724 5351 5653
0154  7651 5640 4215 4612  7611 1341 6733 6751  5675 5661 4215 4612
0170  7211 7746 5362 4240  7352 4675 5655 5661  5752 0676 5273 6752
0204  4255 6651 4212 4611  7611 1341 6733 6752  7675 1341 5333 6752
0220  5261 5735 6741 5762  5752 5735 4215 4612  7211 7746 5362 4240
0234  5752 0275 5673 6352  5262 4252 6703 2717  5316 6724 5751 0655
0250  7251 5273 5253 4653  4215 4612 7611 0211  7365 1764 5250 0247
0264  5647 5651 4215 4612  7211 7746 5362 4240  5752 0675 5673 6352
0300  5751 0653 5273 5752  4253 6651 4212 4611  7611 1360 7751 2356
0314  5346 1250 7245 2264  7242 0654 7362 5333  5735 5651 4215 4612
0330  7611 1360 7751 2356  5346 1250 6734 6362  5356 4642 4273 5215
0344  4211 6775 7612 0211  7362 7351 5364 4346  7242 7703 7355 6360
0360  7345 2764 7744 1334  5334 1356 4251 6673  4212 6775 0212 0232
0374  0000 0000 0000 0000
Non-fatal error encountered in scripts/test/ocomp.os8 at line 5:
	ocomp TTY:<PS.C

Note how os8-run complains about a non-fatal error. Again, this is because the use-case is for detecting two identical files, and calling everything else a failure.

begin / end — Complex conditionals and sub-command blocks.

begin keyword argument

end keyword

keyword is either one of the following:

cdprog Command loop through OS/8 Command Decoder with argument specifying
an OS/8 executable program by name and (optionally) device.
build BUILD command interpreter with dialogs manged with Python expect.
enabled Execution block only if argument is enabled. (See the enable disable) section below.
default Execution block that runs by default but is ignored if argument is disabled.
(See the enable disable section below.)
version Execution block that runs if the current version of the os8-run
scripting language is equal to or greater than the specified version string.
(See version test below.)

For cdprog, and build, argument is passed uninterpreted to the OS/8 RUN command. It is expected that argument will be the name of an executable, optionally prefixed by a device specification. This enables running the OS/8 command from specific devices. This is necessary for running specific BUILD command for construction of system images for specific versions of OS/8 that are different from the default run image.


Run FOTP.SV from device RKA0 and cycle through the command decoder to copy files onto a DECtape under construction from two different places: the old system on RKA0: and the newly built components from RKB1:.

begin cdprog RKA0:FOTP.SV
end cdprog RKA0:FOTP.SV

The build command has had a lot of work put into parsing dialogs. This enables not only device driver related BUILD commands of LOAD, UNLOAD, ENABLE and DISABLE, but also answers "yes" to the "ZERO SYS" question when the BOOT command is issued on a brand new image file.


Build a rudimentary system for a TC08 DECtape.

begin build SYS:BUILD
end build

Most importantly there is full support for the dialog with the BUILD command within the BUILD program to create a new OS/8 system head with new versions of OS8.BN and CD.BN assembled from source.


To create a system tape with new OS/8 Keyboard Monitor and Command Decoder, the above example would add the following just before the BOOT line:


Note: OS/8 disables the BUILD command within the BUILD program after it has been issued during a run. Traditionally, the first action after a BOOT of a newly built system is to SAVE the just executed memory image of BUILD. That saves all the device configurations, but also saves a version with the BUILD command within the BUILD program disabled.

For this reason, you have to run a fresh version of BUILD from distribution media rather than one saved from a previous run. This situation is what drove support for the argument specifier to name the location of the program to run rather than always running from a default location.

Also, BUILD is too sensitive to the location of the OS8.BN and CD.BN files. It pretty much only works if you use PTR: or DSK:. Anything else seems to just hang. I believe the root cause is that, although the device and file are parsed, the actual device has to be either PTR: or the active system device.

os8-run contains two lists of keywords that have been set as enabled or disabled. The setting is done either with os8-run command line arguments or with the enable and disable commands (documented below.)

Two lists are required because default behavior is different for enablement versus disablement.

The begin enabled block is only executed if the enabled list contains the keyword. If no such keyword is found, the block is ignored.

The begin default block is executed by default unless the disabled list contains the keyword. If such a keyword is found, the block is ignored.

The default construct allows creation of scripts with conditional execution without worrying about informing the build system about new enablement keywords.

All these conditional and sub-command blocks must terminate with an end command. The keyword of the end command must always match the begin command. The argument of enabled and default blocks must also match. Nesting is possible, but care should be exercised to avoid crossing nesting boundaries.

For example:

begin enabled outer
begin enabled inner
end enabled inner
end enabled outer

is correct, but:

begin enabled first
begin enabled second
end enabled first
end enabled second

is an error.

enable / disable — Set an enablement or disablement.

enable keyword

disable keyword

The enable and disable commands are used within scripts to dynamically set enablement and disablement. This expands the scope of conditional execution beyond setting passed in from the os8-run command line.

As mentioned above, there are two lists of keywords, one for enabled keywords and one for disabled keywords.

The enable command not only adds the keyword to the enabled list. It also looks for the keyword on the disabled list. If the keyword is found on the disabled list, it is removed.

Similarly, the disable command adds the keyword to the disabled list, and searches the enabled list for the keyword. If it is found on the enabled list, it is removed.

A keyword, will appear only once, if present at all, and will be on only one of the two lists.

The rule is: Last action wins.

Why all this complexity? Here is an example we tripped over and had to implement: We normally apply patches to the version of FUTIL that came on the OS/8 v3d distribution DECtapes. We also have an add-on for the MACREL assembler. That add-on contains a version of FUTIL with updates required to work with binaries assembled with MACREL v2. The v3d-rk05.os8 script needed to either avoid trying to patch an updated FUTIL if MACREL was present, or to perform the patching action if MACREL was not present.

A further complication is that we opt in to including the MACREL add-on by default. We deal with this triple negative by setting disable futil_patch by default, unless macrel gets disabled:

# MACREL is enabled by default with no settings.
# We need to avoid patching FUTIL in that default case
# So we have to set a disablement of that action
# Conditional on macrel default as well.

begin default macrel
disable futil_patch
end default macrel

begin default futil_patch
# The two FUTIL patches only get applied to FUTIL V7 which comes with
# OS/8 V3D to bring it up to V7D.
# MACREL V2 comes with FUTIL V8B, so these patches are skipped
# unless we pass --disable os8-macrel to configure.
patch ../media/os8/patches/FUTIL-31.21.1M-v7B.patch8
patch ../media/os8/patches/FUTIL-31.21.2M-v7D.patch8
end default futil_patch

version test

The os8-run scripting language is expected to evolve over time. An internal language version number is kept, and incremented when major or minor changes are made to the language.

This version numbering scheme can be detected and acted upon within a script by specifying a version match string in a begin / end block.

The language version string is sequence of numerical sub version numbers of arbitrary depth separated by periods. Examples of valid language version strings:


Each sub version is an integer of arbitrary precision.

Clarifying exmple: 3.10 is higher than 3.1.0.

No whitespace is allowed within a version match string.

Therefore a conditional block requiring language version 2.0 and higher would look like this:

begin version 2.0
# The symprini command exists only in version 2 and above.
end version 2.0

patch — Run a patch file.

patch patch-file-path

Run patch-file-path file as a script that uses ODT or FUTIL to patch the booted system image.

configure — Perform specific SIMH configuration activities.

configure device setting

The settings are device specific:

-------- ---------------------------------------------------------------
tape DECtape device settings
dt Set TC08 operation by enabling dt as the SIMH DECtape device.
td Set TD8e operation by enabling td as the SIMH DECTape device.
-------- ---------------------------------------------------------------
tti Console terminal input device settings
KSR Upper case only operation. Typed lower case characters
are upcased automatically before being sent to OS/8
7b SIMH 7bit mode. All characters are passed to OS/8
without case conversion.
-------- ---------------------------------------------------------------
rx Floppy Disk device settings
RX8E Set the SIMH rx to RX8E mode compatible with RX01
Floppy Disk Drives.
RX28 Set the SIMH rx to RX28 mode compatible with RX02
Floppy Disk Drives.
rx01 Synonym for the RX8E option. Compatible with RX01.
rx02 Synonym for the RX28 option. Compatible with RX02.
-------- ---------------------------------------------------------------

This command allows reconfiguration of the SIMH devices during the execution of a os8-run script. This command makes it possible to create system images for hardware configurations that are not what are commony used for OS/8 operation under SIMH.

The best example is the dichotomy between TD8e and TC08 DECTape.

TC08 is a DMA device. It is trivial to emulate. The SIMH device driver simply copies blocks around in the .tu56 DECtape image.

TD8e is an inexpensive, DECtape interface on a single hex width card for PDP8 hardware supporting the Omnibus&tm. The CPU does most of the work. Although a SIMH emulation is available for TD8e, it runs perceptably and often unacceptably more slowly than the simple TC08 emulation.

However, hardware in the field most often has the TD8e DECtape because it was inexpensive.

By allowing reconfiguration inside a script, we can use TC08 by default, switch to TD8e to run BUILD and create .tu55 tape images suitable for deployment on commonly found hardware out in the real world.




Copyright © 2018 by Bill Cattey and Warren Young. Licensed under the terms of the SIMH license.