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20ms is definitely ok provided the Javascript isn't adding too much. I'll do some more playing around.
At 4Mbps it seemed to me there were two issues:
- At a macro level, the time taken between each scan line of data, ie. each spi.write() becomes significant compared to the time taken to send a Uint8Array (single scan line)
- At a micro level, the time taken between each byte becomes noticeable
- At a macro level, the time taken between each scan line of data, ie. each spi.write() becomes significant compared to the time taken to send a Uint8Array (single scan line)
jugglingcats
Nice - thanks! So you're finding that at 4Mbps it's not able to saturate the link?
I think to top that we'd probably going to have to look at DMA - but 20ms update isn't bad, especially since the LCDs usually blur when you update them much above 20fps.
You might be able to squeeze a bit more out of the 'flip' routine by unrolling the loop and doing some things like that though - I imagine there are still gaps from the JS execution speed.