PiDP-8/I Software

install and enable the replacement systemd user service.

[svinit]:  https://en.wikipedia.org/wiki/Init#SysV-style
[systemd]: https://www.freedesktop.org/wiki/Software/systemd/


<a id="options"></a>
### Configure Script Options

You can change many things about the way the software is built and
installed by giving options to the `configure` script:


<a id="prefix"></a>
#### --prefix

Perhaps the most widely useful `configure` script option is `--prefix`,
which lets you override the default installation directory, `/opt/pidp8i`.
There are many good reasons to change where the software gets installed,
but the default is also a good one, so unless you know for a fact that
you want to change this default, leave it alone.

is not the case, since the installation script needs root privileges to
mark a few of the executables as having permission to run at high priority
levels, which improves the quality of the display, particularly with the
[incandescent lamp simulator][ils] feature enabled.


<a id="lowercase"></a>
#### --lowercase

The American Standards Association (predecessor to ANSI) delivered the
second major version of the ASCII character encoding standard the same
year the first PDP-8 came out, 1965. The big new addition? Lowercase.

That bit of history means that when the PDP-8 was new, lowercase was a
fancy new feature in the computing industry. That, plus the memory

    enabling **upper** mode.

[sa]:  http://homepage.cs.uiowa.edu/~jones/pdp8/faqs/#charsets
[tty]: https://tangentsoft.com/pidp8i/wiki?name=OS/8+Console+TTY+Setup


<a id="nls"></a>
#### --no-lamp-simulator

If you build the software on a multi-core host, the PDP-8/I simulator is
normally built with the [incandescent lamp simulator][ils] feature,
which drives the LEDs in a way that mimics the incandescent lamps used
in the original PDP-8/I. (We call this the ILS for short.) This feature
currently takes too much CPU power to run on anything but a multi-core
Raspberry Pi, currently limited to the Pi 2 and Pi 3 series.

If you configure the software on a single-core Pi — models A+, B+, and
Zero — the simulator uses the original low-CPU-usage LED driving method
instead. (a.k.a. NLS for short, named after this configuration option.)

Those on a multi-core host who want this low-CPU-usage LED driving
method can give the `--no-lamp-simulator` option to `configure`.  This
method not only uses less CPU, which may be helpful if you're trying to
run a lot of background tasks on your Pi 2 or Pi 3, it can also be
helpful when the CPU is [heavily throttled][thro].


<a id="serial-mod"></a>
#### --serial-mod

If you have done [Oscar's serial mod][sm1] to your PiDP-8/I PCB and the
Raspberry Pi you have connected to it, add `--serial-mod` to the
`configure` command above.

If you do not give this flag at `configure` time with these hardware
modifications in place, the front panel will not work correctly, and
trying to run the software may even crash the Pi.

If you give this flag and your PCBs are *not* modified, most of the
hardware will work correctly, but several lights and switches will not
work correctly.


<a id="alt-serial-mod"></a>
#### --alt-serial-mod

This flag is for an [alternative serial mod by James L-W][sm2]. It
doesn't require mods to the Pi, and the mods to the PiDP-8/I board are
different from Oscar's.  This flag changes the GPIO code to work with
these modifications to the PiDP-8/I circuit design.

See the linked mailing list thread for details.

As with `--serial-mod`, you should only enable this flag if you have
actually done the mods as specified by James L-W.

This option is a pure alternative to [`--serial-mod`](#serial-mod): you
can leave both off, but you cannot pass both.


#### --throttle

See [`README-throttle.md`][thro] for the values this option takes.  If
you don't give this option, the simulator runs as fast as possible, more
or less.


<a id="savestate"></a>
#### --enable-savestate

By default, the PiDP-8/I starts up with the core state undefined and
runs the boot script you’ve selected either with the IF switches or by
passing it on the command line to `pidp8i-sim` or `pdp8`.  This brings
the simulator up in a known state, with no persistence between restarts
other than what was written to the simulated storage devices before the
last shutdown.

    DEP MQ 0
    DEP PC 0

That zeroes the key registers and prevents the CPU from running as it
normally would after giving the `RESTORE` command to SIMH.


#### --disable-usb-automount

When you install the software on a [systemd][systemd]-based Linux
system, we normally configure the OS to automatically mount USB drives
when they are initially plugged in, which allows the `SING_STEP` + `DF`
media image auto-attach feature to work smoothly. That is, if you plug
in a USB memory stick holding a `*.pt` file containing a paper tape
image, you want the simulator to be able to find it if you have the DF
switches set to 1, telling the PiDP-8/I front panel code to look for
something to attach to the simulator's paper tape reader.

This feature may interfere with other uses of USB, such as when booting
your Pi from an external USB hard disk drive. Give this option to
disable the feature.

(Alternately, you could modify our `etc/udev.rules` and/or
`bin/usb-mount` scripts so that they work cooperatively with your local
USB setup rather than conflicting with it.)


#### --disable-cc8-cross

Give this option if you do not want to build Ian Schofield's `cc8` C
cross-compiler on the host.

Because the cross-compiler is needed to build the CC8 native OS/8
compiler, disabling the cross-compiler also causes the native compiler
to be left off the bootable OS/8 RK05 disk image, as if you’d passed the
`--disable-os8-cc8` configuration option.


<a id="disable-os8"></a>
#### --disable-os8-\*

Several default components of the [OS/8 RK05 disk image](#os8di) used by
boot options IF=0 and IF=7 can be left out to save space and build time:

*   **--disable-os8-advent** — Leave out the [Adventure][advent] game.

*   **--disable-os8-ba** - Leave out the BASIC games and demos which

[advent]: http://www.rickmurphy.net/advent
[chess]:  https://chessprogramming.wikispaces.com/CHEKMO-II
[os8p]:   https://tangentsoft.com/pidp8i/doc/trunk/doc/os8-patching.md


<a id="enable-os8"></a>
#### --enable-os8-\*

There are a few file sets not normally installed to the [OS/8 RK05 disk
image](#os8di) used by boot options IF=0 and IF=7. You can install them
with the following options:

*   **--enable-os8-music** — The `*.MU` music scores and Rich Wilson's
    associated compiler (`MUSIC.PA`) and player overlay (`PLAYOV.PA`)

    FOCAL, so we might then choose to switch the defaults, but that is
    just speculation at the time of this writing.

[f69]:   https://tangentsoft.com/pidp8i/wiki?name=Running+FOCAL%2C1969
[suppd]: https://tangentsoft.com/pidp8i/doc/trunk/doc/uwfocal-manual-supp.md#diffs


#### --os8-minimal

If you set this flag, it sets all `--enable-os8-*` flags to false and
all `--disable-os8-*` flags to true.  If you give this along with any
`--enable-os8-*` option, minimal mode overrides it.  Alas, the only way
to get "minimal plus one or two features" is to explicitly disable all
of the optional OS/8 features you don't want.

    minimal OS/8 bin disk and no src disk, give that option as well.

3.  Although it disables *display* of the `INIT.TX` file on boot, the
    file is still generated in case you later want to enable it, since
    the file acts as build documentation as well as a "welcome" message.


#### --help

Run `./configure --help` for more information on your options here.


<a id="runtime"></a>
## Runtime Configuration