29 Dec
2016
29 Dec
'16
7:43 a.m.
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