Creating MAME errors to help fix PCB errors

Radford119

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Donor 2011, 2023
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Does anyone have any experience in purposely creating errors in MAME ROMs to help diagnose PCB issues? Is this a viable method to try to target PCB issues? I have seen braze's example regarding his DK error screens, but what about modern boards? Can you simulate a RAM or CPU failure?

Sorry for the mass amount of questions and thanks for any info you guys have.
 
I've done this. I usually just keep a 0 KB file sitting around in the ROM directory of the board I'm working with, rename the original ROM, copy the 0 KB file to the original ROM name, test. If I need to try the next ROM, I delete the 0 KB file, rename the original ROM back and move on to the next one. You can move through a board pretty fast this way.

I usually keep two DOS windows open, one with the copy/delete/rename commands in the keyboard buffer and one with the MAME command. Then you can launch quickly after modification.

I haven't figured out how to mimic a RAM error yet.

Edit: From a command prompt, you can create a 0 KB file by typing 'copy con filename.dat' (without the quotes). Then immediately hit CTRL-Z, and it will write the file. Filename.dat can be whatever you want the file called.
 
Not sure what MAME does when it gets a 0-byte file in lieu of a finite size file. I'd guess it fills (or leaves) it zeros (0x00).

According to Scott Brasington (http://www.brasington.org/arcade/tech/mame.shtml) an EPROM is apt to fail such that it always reads 0xFF.

You favorate binary editor (or perhaps EPROM software allows editing/filling the buffer) can do the job of creating you a file full of 0xFF. Presumably it would be handy to keep a set of files of common EPROM sizes (2kB, 4kB, 8kB etc.) filled with 0xFF.

All that said, I've never used this technique. I'd rather just read & verify the EPROMs.
 
I've used this method heavily when working on boards with surface-mount ROMs or mask ROMs where I'm uncomfortable removing them (fragile) or unsure what to read them as on my burner.

I've not seen an issue just using the 0 KB filler, but I've also not tried it with a filled ROM image (all FF).
 
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