OS/8 FORTRAN IV

[Charles Dickman]

On Thu, Dec 29, 2016 at 6:24 AM, Rick Murphy <rick at rickmurphy.net> wrote:

> You could verify by writing a simple toggle-in that does the skip to test:
> 0200/ 6661  - skip on the flag
> 0201/ 7402 - halt if it doesn't skip
> 0202/ 6662 - clear the flag
> 0203/ 6661 - did that clear it?
> 0204/ 7402 - yes
> 0205/ 7402 - no

I single stepped through that section of FRTS and 6661 definitely skips.

> The FRTS does the following:
> LPTEST, LSF
>         IFNZRO LPTEST-415 <****ERROR.....Change Loader****>
>         JMP     NOTLPT
> LPTLCF, LCF             /CLEAR FLAG
>         TAD I   LPGET
>         SNA CLA         /CHECK FOR SPURIOUS INTERRUPT
> JMPDIS, JMP     DISMIS  /GO AWAY IF SO
>
> So, it's skipping, then clearing the flag. So, if there was real hardware,
> this would only trigger once.
> Try the above on a minimal system, then add boards until the problem comes
> back.

I did that last night, but it didn't go away,

Duh! I think I figured it out. There IS an LPT interface. I have a
32kW memory that I build up many years ago and I included a printer
port on it. I haven't used it in eons and I forgot it was even there.
I will have to figure out how to disable it. I don't remember if it
did interrupts or not. There is also a PIO interface for IDE disks on
there.

>     -Rick

-chuck