Quote from: BigJRepairs on February 07, 2014, 08:00:38 PM

It's DVDD adjustment right? Ideally the maximum hash rate you could get would be around 1.1V at 2A Iop, Frequency = ?

Yes, it's DVDD adjustment. The max hash rate with my firmware is achieved at speed=1650 to speed=1750-1800 which may not be the same as the chip's operating frequency but it yields precisely that hashrate (i.e. 16.5GH/s for speed=1650, etc). The DVDD voltage we're using at these speeds is always below 1.06V. When measuring the voltage, be sure to attach both of your voltmeter's probes to decoupling capacitors near the chips. Otherwise measurement results may be distorted due to voltage drops across wires as high currents are flowing through them.

You should start with lower speed values like 1000, slowly raising them up while improving your thermal design and VDD setting. Once you have established a reliable operation at a lower speed, you can go higher.

Quote from: BigJRepairs on February 07, 2014, 08:00:38 PM

were you measuring the operating current per chip or measuring the power consumption of the board?

I was measuring power consumption of the board and then recalculating values into DVDD current given a rated voltage converter efficiency and budgeting some 3W for 3.3V supply current. It's hard to measure DVDD current directly because the current is high and because it's hard to break DVDD circuit at one location in order to insert an ampermeter there.

Quote from: BigJRepairs on February 07, 2014, 08:00:38 PM

I also noticed you're chips running at 35C, how long have you been able to sustain that?

Indefinitely. Our thermal design is very capable, involving heatsinks on both sides of the PCB. The thermistor was physically attached to one of the per-chip top side heatsinks and protected from forced air cooling by a layer of glue and a piece of plastic, so as not to distort measurement results due to sensor cooling. The top side heatsinks were also not very hot on touch. However, these results may still be inaccurate because of the very nature of measuring temperature with thermistors. I'm going to try the more accurate chip thermal sensors, namely MCP9700A. Also there are no means of measuring the chips' junction temperature. With heatsinks occupying all the space around the chips, you could only mount a thermal sensor on the heatsink, and then your results will depend on quality of thermal coupling between the chip and the heatsink. So even with better sensors, any temperature measurement of this kind should be considered only approximate.
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