Ok guys, updating a little bit, because I have a lot.
First, I think my r9 285 cannot be recovered, not even with electrical mod by disabling the bios memory. The thing is ATIflash through DOS is not updated to support Tonga. I realized it when testing with a 380 of a friend of mine. It was not detecting the gpu no matter what. So even I managed to bypass the bios memory, I think it would be impossible.
I've also tried a few things, like swapping the gpu when in windows, but as long as I connect the 285 it's pops an instant bsod.
After tons of days I've finally given up and bought a new r9 380 4GB Nitro. Guys, I think I've found how to tweak voltages for Tonga to, not only reach much higher frequencies, but also to reduce the heat produced.
The key is to change the voltages from the last line of the table2. Since Tonga has a dynamic voltage range, there's more than one voltage to consider:
- Red circle (value1) affects the high range and has a huge impact on the temperatures seen in the gpu. As strange as it might be, +0.05v increased the temps by about 4-5ºC.
- Blue circles (value2 and 3) are the low and mid range. This are the most important to look for stability.
- Orange circle voltage (value0) seems to be the target the gpu will ask. I once left with the stock value of 63288 and it crashed when booting a game.
Having that in mind, the reason why overclocking Tonga is such weird seems to be because the stock range is too wide. The stability is determined by the low voltages, and that's why some gpus need +100mV to get just 1150MHz. The +mV also affects the high voltage, making the gpu eating insane voltages and increasing a lot the temperature.
So far, I can do 1200/1625 with these voltages, without needed to add +mV. Temps are quite good, 81-82ºC with fans at 68%.
And now the best thing. Extreme clocks like these...
The benchmark didn't finished and I was seeing some artifacts, but the bios used was not stable at 1200. And yes, 1275MHz cooled by air at 78-79ºC.
PD: Max voltage read in TRIXX is 1.304v for 1200 and 1.344v when tested 1275.