GDEmu Project News

December 29th, 2012, 01:47 Posted By: wraggster

via http://dknute.livejournal.com/41548.html

I might not belive that the world will end this December but two of my PCs decided not to wait and commited suicide.

My netbook died first, about a month ago, one day simply didn't turn on and that was it. No amount of messing with its internals would help. It was an old hand-me-down with Atom N270 that I got for free because of failed HDD. I replaced it, reinstalled OS and kept using it for a year or so. It had Win XP, 1024x600 matte screen, 1G of RAM and the battery would hold for about 2 hours - which was good enough for my needs. Hell, it flew with me around Europe a few times. I wasn't using it much at home so I don't need to replace it right away but I sure miss it.

Yesterday another N270 gave up the ghost, this time it was my Linux system that I keep running 24/7 for various purposes: router for my private LAN, WiFi AP, FTP/NFS server, and most importantly my dev machine for Dreamcast and NAOMI since I keep my cross-compiler tools there. I liked this board too, it was all-passive cooled and required only 12V input from a brick-type PSU so there were no fans at all. I think the BGA balls cracked because I would get random reboots lately and last week the system would not boot up until it has cooled down to room temperature. Eventually even that stopped working and now it will reboot randomly within 10 seconds of powering up, cold or not. So, right now half of my flat has no Internet and I need to fix that ASAP.

I ordered a new board, it's another Atom (N2800 this time) since I really want to keep the energy usage down to bare minimum and I don't need a lot of CPU power. Even N270 could easily deal with 100Mb/s traffic on both NICs while streaming from HDD, and it was 2.5W rated. Yeah, I know, it doesn't include the north bridge which was doing most of the job connecting all system components together So N2800 might be 6.5W but I expect NM10 to have improved over the old 945 (and GPU is now part of the CPU as well). I was also interested in AMD Brazos family but those chips are much more powerful and require active cooling, and I don't need Radeon HD in a headless PC. The good news is the new board will also be powered by single 12V so at least I get to keep the PSU - hopefully. I already had to buy a new memory stick (DDR3 now instead of DDR2), a new low-profile NIC (no PCI slot, just one PCI-E x1), and a new N-capable WiFi card (miniPCI-E). Well, at least my netbook HDD is going to be reused :P

There is one more old PC that I have, and obviously my main one that is not very old but it has its years. I swear, one of them dies in the next few weeks and I'm buying a replacement and calling it Apollo 13. In the meantime I started doing more frequent backups.

Anyway, so what's up with the GDEMU project. Well, there is progress but I've hit some problems - as usual. I came up with new logic for the FPGA and it works perfectly (so far) between MCU and FPGA but fails on the GD bus. And I have no idea why, I've tried pretty much everything by now, except adding some pull-ups to control lines but I don't expect this to help much. Doesn't look like an electrical problem.
The prototype works when FPGA is clocked within a very specific frequency range, but not really otherwise. BIOS loads the game, I get to see the first screen or so and then it dies because DMA goes completly out of sync - I still have tons of data in the buffer but the console expects to see end-of-DMA interrupt already. So obviously I'm missing a lot of read requests but I don't know why. Must be another race condition that I can't figure out. So, why not let it run at the frequency it works? Because the problem is still there, just not as obvious. It's not stable either way and you wouldn't want your game to freeze 3 hours in and who knows how long since last save, right?

To combat that I've finally gave in and bought USB based JTAG programmer for Altera FPGAs. Those things are costly but I found a cheap clone that should work nice. I expect it to arrive in a few days. With live JTAG uplink I will be able to transfer new settings directly rather than have to swap SD cards as I do now, and more importantly I'll be able to run a logic analyzer to see what is going on.

The world will most likely not end but thanks to all those troubles (and GoG discounts my bank account balance just might.



EDIT: Looks like it could be electrical issue after all. Well, I'm going to rip the Dreamcast apart now and solder some proper wires for ground return path. Lets see what that does.

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