Octal boot code?

[Jeff Shrager]

Hi. Is there a way to replace the boot so that it's as if I stopped the machine, toggled in a program The Hard Way, and then loaded the start address and hit start?

Thanks!

[timr...@gmail.com]

Pretty sure you can tell Simh to "deposit" values into simulated memory. So if you have the boot code you could add a series of deposits to the Simh boot script.

Are you trying to boot some system that is not already part of the PiDP-8i?  Or do you just have the Rasp Pi and no PiDP?  This get tiring after awhile.  Take my word

for it having to do this on a real pdp-8i too many times.

[Steve Tockey]

Jeff,

There's no need to worry about boot code at all to do that. At any point, you can just hit the Stop switch on the front panel. Now, all (well, most anyway--depending on what version of the PiDP-8/i you are running) of the front panel switches and lights are the same as on a real PDP-8/i. You can set bit patterns in the Switch Register, hit Load Address, Dep(osit) things, Start, and generally have all kinds of fun doing things the way we did them "back in the day". This includes toggling in whatever boot program you want. Or any other machine code you want.

If you haven't already got it, you might want to grab a copy of the 1970 edition of DEC's Small Computer Handbook:

https://bitsavers.org/pdf/dec/pdp8/handbooks/SmallComputerHandbook_1970.pdf

Chapter 2 covers front panel operations: what all the switches do and what all the lights mean. Chapters 3 and 4 cover the PDP-8 instruction set.

Sure, you can deposit, exam, and run using SIMH but that's the easy way (smile). The Real Programmer's way is through the front panel.

The bottom line is that you don't have to do anything boot-wise, it's just a matter of stopping the machine and then fiddling with the switches.

Happy hacking,

-- steve

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[Jeff Shrager]

Thanks, all. I don't think that I was clear enough in my question. I know what I can toggle in code and run it. In fact, as you point out, that's a huge part of the point. :-) And that's what I've been doing. But I have a favorite program that about 50 words, and when we have a power failure, or someone unplugs the power, I have to toggle it all back in. As Tim points out, that gets old fast. So I was hoping that I could basically preload my 50 words in a boot config text file someplace and get it to preload and start when the thing boots up.

Thanks!

'Jeff

[Steve Tockey]

Jeff,

Sorry, looks like I misunderstood your question. You are wanting boot scripts that do different things? That's also not a problem. There are three parts to the trick, I believe.

1) Boot scripts for the PiDP-8/I are, by default, in the Pi OS directory /opt/pidp8i/share/boot. Many examples are in there.. In particular, you may want to look at hello.script and bit-rotate-script as examples of what I think you're trying to accomplish. You can just make your own .script file in that directory, calling it whatever you want.

2) You can force execution of any boot script you want. For sake of argument, let's say you made your own script and called it myscript.script. In a running instance of PiDP-8/i SIMH, type ctrl/e to drop into SIMH. From the sim> prompt, you can then type:

sim> do /opt/pidp8i/share/boot/myscript.script

You can also:

sim> cd /opt/pidp8i/share/boot

sim> do myscript.script

doing the cd is particularly useful if you want to fiddle around with many different scripts in the same session.

3) If you name your script with a single octal digit with .script as the extension, then you can set that bit pattern in the IF switches and when you boot the PiDP-8/I it will execute that script. For example, I have replaced the original 6.script with my own version that boots into EduSystem-20C BASIC. If you go this route, you might want to make a backup copy of the original X.script so you can get back to it, although you can also find it in the source code tree form when you built SIMH.

Hope this is what you were looking for,

-- steve

On Thursday, March 13, 2025 at 11:29:29 AM UTC-7 Steve Tockey wrote:

[Tim Radde]

He explicitly asked is there a way to make like he stopped the machine, toggled in some program (the hard way) and then load the start address and hit start.  So it seems he does not want to actually toggle the switches.  He may not have switches.

[timr...@gmail.com]

Ah, I see what he wants to do now.  A 50 byte toggle in is not fun.  I liked the OS/8 boot script on the 8e for the RK05.  Two bytes.

[Jeff Shrager]

Thanks, all. Esp. @SteveTockey ... worked as described first try!

'Jeff