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by reerdna 1193 days ago
Yes, it's nearly always in active mode now. I haven't done much to use the sleep modes at all, only "sleep until next keyboard interrupt" when the program calls (get-key). Measurement, selected portion is while rendering a fractal - so "100% cpu" - at 1.5mA. https://cdn.hackaday.io/images/4389961676068300828.png

I'm sure other uCs could sleep at lower power, but active mode was what I wanted to optimize for.
1 comments
kragen 1193 days ago
This is wonderful information! Thank you! That's 1.49 mA at 3.3 volts?
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reerdna 1193 days ago
Yeah, matching pretty well the advertised 5mW. But uLisp is probably not using the CPU very efficiently and so not driving it to the max that could perhaps be seen with something like a well-implemented FFT.
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kragen 1193 days ago
Is this at 48 MHz or 96 MHz? I'm so confused about the 96 MHz stuff in the datasheet. There must be some drawback to 96 MHz, because if not, what's so special about 48 MHz?

Is that using the FPU, or are you doing all the fractal math in integer? I have this vague idea that using the FPU might cause it to use more power than integer code will (and might or might not be faster for fractal rendering).

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reerdna 1193 days ago
Using the FPU I believe but quite inefficiently, most cycles are probably spent in integer operations and chasing linked lists for the lisp parser. http://forum.ulisp.com/t/barnsley-fern-in-ulisp/1087

48MHz is the most power efficient mode, you can run it at 96Mhz "burst mode" but apparently it uses disproportionately more power, I have not measured how much.

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kragen 1193 days ago
It's really exciting to see this stuff coming to life!

Does this display have the same nominal 2Mbps speed as the 2.7" one I've been using? I've seen people report that it works well at 6Mbps (and thus 60 Hz) but haven't tried it myself. I'm guessing that it would use more power.

Have you been able to measure how much of the power consumption is the display?

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reerdna 1193 days ago
Yes, I'm running the display SPI at 2MHz which is ~25 fps. Overclocking it to twice as fast works just fine but uses significantly more power as expected. I did not try to go further.

Approximately 25%-50% of the total power depending on refresh rate. Worst case seems to be alternating black and white pixels, maximizing the number of transitions?

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