getBlocks(false) - Still taking way too long - Why?

srepmub · June 23, 2022, 4:08pm

hi all,

I was also struggling a bit with getBlocks(false) still seeming slow (I need a very fast loop() execution). then I came across discussions about how the builtin Wire library is not fully non-blocking… and played around with nI2C or non-blocking I2C: https://github.com/nitacku/nI2C. that worked out rather well, and my loop() is now much much faster (though to be honest, I may not have used the Pixy2 library correctly; OTOH, I really like it if everything is non-blocking… :P). here is an simple sketch that I made today to call getblocks on two pixies: https://github.com/srepmub/tacovr.

thanks, cheers,
mark.

edge · June 24, 2022, 1:35am

Hello,
Have you timed how long getBlocks(false) takes? A few milliseconds is reasonable.

Edward

srepmub · June 24, 2022, 7:23am

hi edward, thanks. I need to call the accelstepper run() functions thousands of times per second, so blocking for a few milliseconds is not that great… I did not know how to measure time before, but using micros() an ni2c read/write call takes about 50 microseconds for me.

edge · June 25, 2022, 1:09am

Hello,
Look at the source code for getBlocks:

github.com

charmedlabs/pixy2/blob/master/src/host/arduino/libraries/Pixy2/Pixy2CCC.h

//
// begin license header
//
// This file is part of Pixy CMUcam5 or "Pixy" for short
//
// All Pixy source code is provided under the terms of the
// GNU General Public License v2 (http://www.gnu.org/licenses/gpl-2.0.html).
// Those wishing to use Pixy source code, software and/or
// technologies under different licensing terms should contact us at
// [email protected]. Such licensing terms are available for
// all portions of the Pixy codebase presented here.
//
// end license header
//
// This file is for defining the Block struct and the Pixy template class version 2.
// (TPixy2).  TPixy takes a communication link as a template parameter so that 
// all communication modes (SPI, I2C and UART) can share the same code.  
//

#ifndef _PIXY2CCC_H

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On line 140, there is a delay command to prevent someone from thrashing Pixy with lots of requests per second. You can remove this delay (modify Pixy2CCC.h) and as long as you keep things reasonable with Pixy (no more than a few hundred requests per second). Pixy will then be able to process frames and find objects in a timely manner and you’ll be able to run more things in your polling loop.

Edward