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Progression on the die, five document lengths x seven trials at each step:
step fixed per char at 160 chars
ReleaseSmall 16.99 ms 54.3 us 25.56 ms
ReleaseFast 14.85 ms 34.7 us 20.30 ms 0.79x
+ ASCII grapheme 14.56 ms 12.0 us 16.46 ms 0.64x
+ ASCII print 14.27 ms 6.9 us 15.36 ms 0.60x
+ shadow grid 8.87 ms 7.3 us 10.02 ms 0.39x
+ byte compare 8.37 ms 7.1 us 9.48 ms 0.37x
Round trip is time to the FIRST response byte: ~1.95 ms of host and USB latency plus
compute. Compute is 6.42 ms and the 4 ms goal needs it under 2.05 ms, so 3.1x remains.
Every microsecond of it is now measured rather than guessed, by stage, on the die:
our walk of the grid 979 us this repo's own present()
vaxis diff + emit 2455 us vaxis walks all 480 cells, per-cell strings
pardes Surface rebuild 2000 us pardes rebuilds every cell every frame
input parse + edit 250 us
The honest reading is that the two large items are not each other's alternative.
vaxis's diff is redundant work - present() already computes exactly which cells moved,
so emitting ANSI directly from the shadow grid would remove most of that 2.46 ms. But
even a perfect renderer leaves pardes rebuilding a whole Surface per keystroke, and 4 ms
at 40x12 needs that too.
Raising the baud does not move this number. At 115200 an 81-byte reply is 7.0 ms of
wire, but almost none of it lands before the first byte; 921600 takes `settle` from
23 ms to ~16 ms and leaves the round trip where it is. Worth doing, not for this.
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