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Faster parity calculations for SerialPIO when using multiple instances #2932

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ahmedarif193 opened this issue May 1, 2025 · 1 comment
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Faster parity calculations for SerialPIO when using multiple instances #2932

ahmedarif193 opened this issue May 1, 2025 · 1 comment

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@ahmedarif193
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Right now, SerialPIO calculates parity with a bit loop that gets slower with more data bits. If you're running several soft serial ports (like 4+), it starts eating CPU for no good reason.

A small lookup table (256 bytes) could do the same job way faster, basically constant time, just a few instructions per byte versus 60+ instructions for 8-bit data for example.

Tradeoffs:

  • Speed: about 10–12x faster per check
  • RAM: 256B global LUT (shared by all instances)
  • Determinism: fixed cost per check

I'm happy to send a PR for this.
ahmedarif193 pushed a commit to ahmedarif193/arduino-pico that referenced this issue May 1, 2025
optimize parity calculations in SerialPIO (earlephilhower#2932)
ec1c8f2 
use LUT for faster parity checks, reduces CPU load with multiple instances
ahmedarif193 pushed a commit to ahmedarif193/arduino-pico that referenced this issue May 1, 2025
optimize parity calculations in SerialPIO (earlephilhower#2932)
abbfc4d 
use bit manipulation technique from http://www.graphics.stanford.edu/~seander/bithacks.html#ParityParallel for parity calculation
ahmedarif193 pushed a commit to ahmedarif193/arduino-pico that referenced this issue May 1, 2025
optimize parity calculations in SerialPIO (earlephilhower#2932)
42cc372 
use bit manipulation technique from http://www.graphics.stanford.edu/~seander/bithacks.html#ParityParallel for parity calculation
earlephilhower pushed a commit that referenced this issue May 1, 2025
@ahmedarif193
optimize parity calculations in SerialPIO (#2932) (#2933)
59614a9 
use bit manipulation technique from http://www.graphics.stanford.edu/~seander/bithacks.html#ParityParallel for parity calculation

Co-authored-by: Ahmed ARIF <contact@eotics.com>
@earlephilhower
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Fixed by #2933

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@earlephilhower @ahmedarif193