exxos's Atari, Amiga & retro forum

Since installing the 2021 16 MHz Booster in my STFM a while back this error, I7 bus error not detected, has popped up when booting the diagnostics cart. I've tried looking up what this actually means but I can't find much about it. The 520STE Field manual has this to say:

I7 Bus Error not detected. Glue not asserting Bus Error or the signal is not reaching the CPU

Ok that doesn't sound great, but it doesn't seem to explain what the bus is for. As far as I can tell, the computer works as it should both in 8 and 16 MHz. It's stable for hours, or at least it doesn't seem to be any more or less prone to crashing than before installing the booster. ACSI HDD interface works, floppy drive, NetUSBee through the cart port. All is well and good.

Furthermore, this is actually the second CPU booster I attempt to install in this computer. The first one I screwed up by putting a socket on it like a dummy so it wouldn't fit in the case anymore, and by attempting to take the socket off I damaged it and it wouldn't boot into TOS afterwards. When checking it with the diagnostics cart, it also displayed the I7 bus error message. So I assumed that was why it wasn't working anymore. I put the original CPU back in while waiting for the new booster. And with the original CPU back in place the I7 bus error went away. But now it's back with the second booster board again.

So is this just expected behavior with the booster? It doesn't seem to actually cause any ill effects, although I haven't tested all the ports on the computer so maybe it's related to one of those? What is the I7 bus? Any hardware gurus that know what this is about?

Thanks for looking.

I'm not 100% about this, but I think you'll need to run diags in 8Mhz for them to work correctly.

Also, you may want to double check the diag cart is set to STE mode and your trying to run it on an STFM, because I don't believe they are compatible.

If the machine is otherwise running fine I'd check those things first.

This question pops up every few months.. I forget the exact particulars but basically it is nothing to worry about..

If I remember rightly the diagnostic cart checks address zero (ROM) for bus error, BUT, this bus error can't be issued on the first few bus cycles as the ROM would never be read and the machine would never boot up. So it has to be done later, with some logic processing.

In terms of the booster, address zero is decoded, but there is not enough LA left in the PLD to process the bus error afterwards. So the diagnostic cart complains that there is an error.. Because there is... But absolutely nothing else to my knowledge even checks for that bus error.. I don't think TOS would even boot up without bus error working anyway.

I half recall later boosters might have had that "feature" added back in, but I don't really remember after all this time now.

Thanks for the input guys. The message pops up in both 8 and 16 MHz, and I'm almost 100% I set it the diag cart to ST mode not STE. But if it is like exxos says that'd explain it. I did search the forums actually but couldn't find anything so apologies for that.

But as I mentioned nothing seems to be actually wrong with the computer... so I'm just not gonna worry about it! :mrgreen:

Thanks again for the input. Much appreciated.