exxos's Atari, Amiga & retro forum

With Kickstart 1.3:
I have a clock frequency on pin 15 and 20.
I also have activity on _AS but only for 15 seconds and then it stops. This behavior is consistent.

With Diagrom:
I have a clock frequency on pin 15 and 20.
There is no activity on _AS

There must be a short burst of activity in the /AS line for it to know that there's a different ROM in the socket as otherwise it wouldn't be able to put the address of the ROM on the bus to read it.

It's quite possible that one of the first things the diag ROM does is access something which is then not generating an acknowledge as so the CPU is sitting there waiting for the bus cyle to end and it never does.

I'm not an Amiga person but from what I remember all I/O access goes through Gary, with only the chip RAM and ROM being on the CPU side of the system. It's there I would start looking.

Thank you.
Other than ensuring there is continuity between each pin on Gary to its destination, the socket isn't corroded, no bad solder joints, a working IC, what in particular should I be looking for? I do notice that _HLT is low on Gary.

Kepler wrote: 12 Jun 2024 16:55 Thank you.
Other than ensuring there is continuity between each pin on Gary to its destination, the socket isn't corroded, no bad solder joints, a working IC, what in particular should I be looking for? I do notice that _HLT is low on Gary.

HALT is connected to the CPU. So its likely the CPU has crashed. Have you put a serial cable on yet? Its possible DiagROM is actually telling you the issue right there on the serial port.

I just connected my laptop via the serial port, started Putty and unfortunately, there was no output.
I didn't think Diagrom would show anything if the _HLT was low?

Kepler wrote: 12 Jun 2024 20:31 I just connected my laptop via the serial port, started Putty and unfortunately, there was no output.
I didn't think Diagrom would show anything if the _HLT was low?

Halt is low because there is was a double bus error. HALT is not just an input to the CPU its also an output.
My guess is you have a data bus or address bus fault.

Have you checked all the card slots to make sure nothing has fallen in and shorted pins out? I know it's unlikely but might be worth a quick check given that the custom chips function in another board... Other than that it's probably going to be get out the schematics and start toning out lines time... and toning actual chip pins to the socket/board trace sides to rule out duff connections... checking vias etc etc

I just checked the expansion/CPU slot, scrutinized the underside, nothing appears suspect.
I am inclined to think it is a broken trace too...unfortunately, I haven't found any broken around the CPU or Kickstart ROM but I will carry on looking.
Thanks for all your help!

If you can extract the CPU and gently lift the /HALT pin, re-insert it into the socket and power up see if the hat is being pulled down by the CPU or Gary. This will tell you if it's the CPU faulting or Gary halting the CPU.
(The pin on the CPU should drift high enough to allow the CPU to run.)

With the _HLT pin raised, the pin registers low and the socket registers high. Therefore, it appears it is the CPU which is causing the halt. Correct?