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I have a faulty Atari 520STFM additional 4MB ram installed. It shows bombs on boot. I understand bombs are sort of code indicator of what is malfunctioning in the system, similar to what Guru Meditation errors are in Amiga machines. What these bombs actually mean in general? Is there a resource like this one for guru errors?

http://www.amigahistory.plus.com/guruguide.html

Boot screen 1

Boot screen 2

Boot screen 3

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    As to what's causing the error, the pattern on the lower part of the screen makes me think something's important is getting overwritten when it shouldn't. You might try re-seating any socketed chips/connectors. I'd also check the board for any dirt or corrosion that could be causing a short. – Alex Hajnal Jul 6 at 1:27
  • BTW: Did you resolve the issue? – Raffzahn Jul 7 at 20:13
  • No, but the answer is very helpful anyway. The board itself needs further inspection, but as always not enough time. – Bartek Malysz Jul 7 at 20:25
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Hint: It would be great if you could extend your question not only with the number of bombs, but as well the setup and conditions used to produce them.


I understand bombs are sort of code indicator of what is malfunctioning in the system,

Jup, they are, so it would be nice if you could tell how many you see, as that is essentially the error code.

similar to what Guru Meditation errors are in Amiga machines.

No. Guru Meditation are explicite software error codes told by the OS (loader). Bombs are hardware traps.

What these bombs actually mean?

Well known (and from memory) are

  • Two (*1) bombs (*2) are a bus/address error, while
  • Three bombs indicate an unaligned word access.
  • Four bombs come with an illegal instruction.
  • Five bombs are a division by zero.
  • ... and so on.

After all, the count of bombs is basically the trap number issued by the error.

Is there a resource like this one for guru errors?

Check the vector list. Bombs aren't OS errors, but hardware exceptions. They simply tell that the CPU took some trap which is not handled otherwise.

In your case it seams to be trap #20 (*3), one of the reserved vectors.

But there's another hint: the bitmap/colour artefacts. While they as well may come from some program running wild, I'm pretty sure the traps put the CPU into a standstill after drawing the bombs, so no chance, which means they must be hardware related. First assumption would be memory, the second the Shifter (graphics/system chip).

In either case it's a good idea to open the baby, check everything, reseat all socketed components and cables and try again. That's the usual magic for old computers anyway.

It's impossible to give any further hint without more information about environment and what you're doing.


*1 - There is no trap vector 0 or 1 as these entries are used for reset values for PC and SP.

*2 - Bombs are BTW only used since TOS-ROMs exist, as the disk version did show little atomic mushrooms.

*3 - As Alex mentiones it may as well be a higher number, if they are only outputed in a single line. I do think they warp into the next, but I'm not sure, so lets say 20 or above.

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    It could be a trap higher than 20 since the ST's screen clips at that point. I don't recall the behavior when such a high trap causes a fault. – Alex Hajnal Jul 6 at 1:30
  • I thought it would continue one line down, but then again, I couldn't find any supporting picture or page, so yeah, 20 or above. – Raffzahn Jul 6 at 10:18

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