Wubs GP32 - Nand replacement.

[rubber_jonnie]

Seeing that thing makes me want to dig out my old GP32 too
Such a nice and quirky handheld at the time. Great work reviving it!

I'm pleased I was able to do so

Great little machine.

[wub]

My apologies to Jon for not updating this thread sooner!

Once I had the unit back it was obvious that something wasn't right and so I started trying to test it, and compare its behaviour to that of my BLU+ unit which works a lot better but still has problems.

The first thing I did was verify that the flash that Jon performed had been successful, which it had. I've tried taking pictures of the screen but even the BLU+ is very difficult to get anything like a clear picture from. What I need is a clear video to show the behaviour of the graphical glitches as I think it suggests a memory problem and I'd like to hear what people here think about that.

I'm still testing things but my suspicion is that what we're looking at here is over-clocking damage and I think it's the memory that has become damaged and not the CPU. I over-clocked all my GP32's, although the BLU+ wasn't used very much after I bought it which would very nicely explain why it works the best out of the three.

The common knowledge at the time was that you could not damage the GP32 by over-clocking. If the CPU was set to run faster than it could handle then it would immediately crash and you would know that that was too fast, select a slower speed, and try again. IIRC the FLU I sent Jon could handle 144mhz and so that was the speed it spent a lot of time running at, for playing the bigger Doom2 wads

The GP32 was over-clocked via software and the instructions to do so set both the CPU and memory timing. If you go looking for the codes for setting different speeds you will quickly notice that there were different solutions for setting the same speed and I wonder if some of these solutions were wrong.

The behaviour of the unit, in general, is that it crashes while loading most programs. Some run perfectly and some run but with corruption to the screen.
Jon noticed the vertical lines of corruption on the main Wind-Ups screen. The GP32 screen is rotated by 90 degrees in memory so those vertical lines are actually sequential bytes of data that have become corrupted.

The apps that do load seem to run perfectly and this includes emulators that are probably hitting the CPU quite hard. If it was CPU damage I wouldn't expect it to be able to run things like this at all, particularly when much more lightweight apps won't even load. For example, the small mini-game Lacuna runs with a lot of graphical corruption, but Another World, which is a far bigger executable and a far more complex game, runs really nicely with no screen corruption at all.

I will keep testing and trying to find some answers but I wanted to thank Jon again for getting it back up and running. Everything he did was a success and the fact the unit is still not working right is not because of anything he did, or didn't do!

[rubber_jonnie]

No need for apologies

As we've discussed separately, your machine definitely had a bad nand as the replacement does let the machine boot, but the data I recovered from the old nand didn't match the firmware file you sent me at all, and the new nand was verified after programming too against the firmware file. So that was a win.

But I agree, something else is astray here and I think you may be onto something regarding the overclocking. I do overclock my BLU+ but like you I always had programs crash when I went too far.

Looking at the GP32 I suppose the next steps could be to do a recap, though I did evaluate yours and saw no signs of leakage when I had it apart it doesn't mean they are good, and/or replacing the RAM which is surface mounted and could easily be swapped out.

Food for thought.