ABug & Homebrew Gaming Weekend, July 11th + 12th

[Multiwizard]

Love the pictures and video's, thanks...


Greetings, Wim...

[davidb]

Here's the picture I promised jgharston. More to come!

[davidb]

Some pictures as promised.

[jgharston]

Couple of clips of the Acorn System Three(?) in action, narration courtesy of JGH:

I've disassembled the ROM image from the System 3 and compared it to the System 5 ROM image I already had. The only differences are that the System 3 is coded to access a 40x25 teletext display, the System 5 is coded to access a 80x25 character display. Other than that, the kernal code is binary identical.

That means that something else is causing the looping Command? errors we were getting when running System BBC BASIC.

[jgharston]

That means that something else is causing the looping Command? errors we were getting when running System BBC BASIC.

Somebody (sorry, I can't remember names) suggested it might be spurious interupts causing a problem. Normally a System runs with IRQs disabled, and checking the code, IRQV jumps to a Command? error, and BBC BASIC starts up by enabling IRQs. So, any random cosmic ray passing by and hitting the IRQ line is going to cause Command? error in the middle of something else.

This matches up with when the error occurs as well. BASIC I enables IRQs in the error handler. BASIC II and III enable IRQs on startup. On the System, BASIC I would bomb out into an error loop only when an error occured, BASIC II and III would bomb out as soon as they started up.

So, pointing IRQV to a handy PLA:RTI would do it (as IRQV is entered with A on the stack), there's one at &F8BE. So, doing ?&204=&BE:?&205=&F8 would do it with BASIC I. You need to do it before entering BASIC II, so create a file that loads to &204 containing the bytes &BE,&F8. In BBC BASIC: ?&204=&BE:?&205=&F8:*SAVE NOIRQ 204 206 (somebody here can say what the Atom BASIC syntax is)

Then, before running SBASIC1, SBASIC2 or SBASIC3 do *LOAD NOIRQ

Or, as a hardware fix, tie that damn IRQ line to something!

[IanS]

Or, as a hardware fix, tie that damn IRQ line to something!

There is pull-up on the cpu card (R4 on that version of the CPU card).

I wonder if the I/O card can generate interrupts. I don't think we tried the system without the I/O card plugged in.

We'll need IRQ for when it gets an Econet card

[Prime]

It looks like the card that we could not identify in the System was possibly the Laboratory Interface. It's listed on the Acorn System catalog available here :

http://www.vintageacorn.com/Acorn_SystemCatalog.pdf

Cheers.

Phill.

[IanS]

And on the same page in the pdf:

The program may be synchronised to real time using interrupts which are generated by circuitry on the interface Eurocard with a periodic time of 10 milli-seconds

We need to try the other Basic versions without that card.

[jgharston]

And on the same page in the pdf:

The program may be synchronised to real time using interrupts which are generated by circuitry on the interface Eurocard with a periodic time of 10 milli-seconds

We need to try the other Basic versions without that card.

I've updated the disk image to contain a *NOIRQ command file which when run points IRQV to a null return, so that should let BBC BASIC run happily.