Atmega1284P Test Results -- UPDATED!

[uze6666]

The atmega1284 and atmega1284P spec sheets show a max voltage rating of 6 volts, though the "safe operating" area shows up to 5.5 volts. It is common knowledge among PC overclockers that increased core voltage is sometimes required to get a processor to overclock well. Have you tried increasing the power supply voltage to the ATmega1284P? You should try up to 6 volts and see if it then works. Also look for a 40 pin slip on heatsink for the processor. If you can't find one just slap a hunk of metal on top of the chip with superglue. Also you might need to use an external oscillator instead of relying on the processor to clock it's own crystal. You might be able to force the atmega1284p to work yet!

These are interesting ideas. This comes with it's own problems unfortunately. Raising the voltage would imply changing the regulator, the video DAC and voltage interfaces to other chips like the SD card. I don't think heat would we an issue as even overclocked the the chip stays cool. An external clock, although much more expensive, could be an idea to try. If anyone else wants to try the suggested ideas, be my guest. To make it simple, the basic B/W design could be used as a PoC. Personally, I won't have time to fiddle more on this until a couple months.

-Uze

[kscharf]

Heat is an enemy of overclocking. Cryogenicly cooled IC's have been overclocked by huge amounts. You may think the chip is running cool, but inside it may be "sweating". Get a can of "Freon" cooler (they don't use real Freon anymore) used to test electronics for faulty parts and spray the cpu till it turns white with frost and see if it works. If it does, then a voltage increase may enable overclocking at room temperature. You could also get one of those peltier cpu cooler modules and attach it to the top of the processor to chill it down. Only the cpu needs to be run at higher voltage, an increase of a half volt may be enough. The DAC resistors may need to be readjusted for best color, but can be left alone for a quick test. You would need a separate voltage regulator for the cpu, putting a 1N4004 in series with the ground lead of a 7805 will raise the output voltage by .6 volts. Voltage level conversion shouldn't be a concern, the difference should be tolerated by the other parts.

I might try building a fuzebox. I'm waiting for adafruit to get the PC boards back in stock. I got the AD part as a sample a while ago.

[uze6666]

Only the cpu needs to be run at higher voltage, an increase of a half volt may be enough. The DAC resistors may need to be readjusted for best color, but can be left alone for a quick test. You would need a separate voltage regulator for the cpu, putting a 1N4004 in series with the ground lead of a 7805 will raise the output voltage by .6 volts. Voltage level conversion shouldn't be a concern, the difference should be tolerated by the other parts.

I had time to test just that and I report...success! It made a heck of a difference, all chips worked fine running all ROMS without crashes or artifact (the Dr.Mario is fine now) ! Check out the tread's main post for more details. The idea of the diode in series is neat since I could not find 5.6V regulators, I will try this out soon. Thanks!

-Uze

[paul]

Now there will be no excuse for a lackluster title screen

Nice work, guys.

[DaveyPocket]

Now what's next? It depends. Raising the voltage has it's side effect. A new Uzebox schematics for the 1284p would be required since the voltage upgrade will impact a lot of things like the video DAC resistor values, voltage dividers for the SD interface, the ad725, controllers, etc. What's more, this will leave Uzebox and Fuzebox owners in the dark since they can't upgrade to this chip directly.

What I think would be a good idea is to create a some sort of daughter board that fits into the 40-pin socket. The atmega1284p will get power from a separate regulator on this board and not from the regulator on the Uzebox.

[uze6666]

I think would be a good idea is to create a some sort of daughter board that fits into the 40-pin socket.

That's a possibility and using a voltage step-up converter would allow to use the main board 5V source. Also, plainly raising the board's voltage to 5.6V (and if the AD725 can withstand it), very few components would need to be replaced (like augmenting the 75ohm resistors to compensate for the elevated voltage). The SD interface has it's own regulator and the controllers seems happy so far.

-Uze

[DaveyPocket]

I think would be a good idea is to create a some sort of daughter board that fits into the 40-pin socket.

That's a possibility and using a voltage step-up converter would allow to use the main board 5V source. Also, plainly raising the board's voltage to 5.6V (and if the AD725 can withstand it), very few components would need to be replaced (like augmenting the 75ohm resistors to compensate for the elevated voltage). The SD interface has it's own regulator and the controllers seems happy so far.

-Uze

One more thing, would raising the voltage affect the controllers at all? (NES and SNES controllers) I don't think it will but it's something to consider.

[uze6666]

I wouldn't be too much concerned about the controllers! The 4021 shift registers used in NES controllers was on the CMOS kind capable of handling VDD of 7 volts or more. The 16-bit SNES version (I heard) was nothing more than two of those cascaded in a chip. I've tried a couple of those cheap after-market SNES controller and they all work fine (if you called their normal operation fine ). Also tried an original SNES without any problems.

Things starts to look interesting again!

-Uze

[Flecko]

That is freaking awesome! Huge possibilites if it proves to work out. I'm excited.

Haven't had a lot of time lately to work on my game...but believe me, I think about the Uzebox and my game all the time...

[D3thAdd3r]

Wow excited to see this, coolest Uzebox advance in a while. Think I could actually fit/complete my games with all the extra space available! Perhaps I'll steal some spare time back from the significant other, can't let them get too spoiled