Nudging things slightly back on topic with some testing.
Here's a GekkoScience Compac hashing away at 16.5Gh/s (300MHz clock):
[youtube.com]
I made a few adjustments to cgminer to show a bit more detail, give an estimate of Work efficiency, time elapsed since last reset/zero, etc.
That info was then used across several frequencies, measuring all the things, and doing further calculations (getting the effective hash rate and effect J/Gh, for example.) The test setup has pretty much been unchanged throughout other than adding a power supply later on. The fan is positioned 10cm above the Compac, so keep that in mind when looking at the temperature deltas; I wouldn't want to leave it passively cooled at the higher frequencies
Note: There's a knee in Vcore in the graph until I test those 'tween frequenciesI did run into a few occasions where the comms chip wasn't doing anything - power draw was pretty much near-zero* - and had to unplug/replug (switch on hub port makes this nice and easy).
* The green LED appears to be using ~3mA. The blue/orange ones together add another ~6mA. This affects efficiency quite minimally, but I'm still glad I taped that LED over a bit.If all went well, and it would initialize and hash normally, potatoscope showed pretty much this (Iusb (dimensionless because what's a current probe? Can derive from graphs above though) at Vcore=~550mV):
If instead it failed to initialize, typically due to too low a Vcore, it would show this (Vcore=~550mV - yes, every once in a while it would be okay):
In that unclean state, more often than not, I had to power cycle the board to get it up and running again.
The other failure mode is in the upper regions of the clock frequency. As more current gets drawn, cheap power supplies drop voltage quite a bit, and the power driver on the board would freak out a bit, producing a nice singing inductor coil:
[youtube.com]
Something to add to my little booklet's FAQ when I get around to updating it for the production versions (would love to know what changes are made there other than pot direction). Solution is to use a better power supply or at least an adjustable one so you can bring Vusb back up. In fact, on several tests, I had to bring Vusb up above 5V to prevent the singing.
As the clock frequency increases, the range in which Vcore will work and Vusb becomes finnicky narrows quite a bit; that's why the little graphs also become more narrow
Suffice to say that I haven't pushed it beyond 0.38J/
[email protected]/s at this time, and haven't yet tweaked things subtly enough (a multi-turn pot would be nice) to get below the 0.339J/
[email protected]/s I've gotten, those are pretty impressive stats for a StickMiner