Due Loop time

Official Hardware Mega Due
1

Hi,
I am developing a product based on the Due and I am having speed issues.

Here is the code I am testing with:

const byte outPin = 41;
Pio* outPort = g_APinDescription[outPin].pPort;
unsigned int outMask = g_APinDescription[outPin].ulPin;

void setup() {
  pinMode(outPin, OUTPUT);  
}

void loop() {
  outPort->PIO_SODR = outMask;
  outPort->PIO_CODR = outMask;
}

This gives a pulse as expected, but the time between pulses is 2.2 uS. I can only guess Arduino is doing background stuff, but it is eating up about 180 clock cycles.

Is there any way to speed this up?

2

You might want to read the "Ethernet2 (UDP) SPI transfers have a lot of dead time" further down the page, some progress has been made :slight_smile:
http://forum.arduino.cc/index.php?topic=437243.0

3

I see similar times, and I don't understand it either :frowning:

Ah. This appears to be due to the SerialEventRun() polling crap in main() Due has 4 serial ports, so that's minimally 4 calls to SerialX.available() I was under the impression that the compile was smart enough to omit that when there were no serial ports in use, but I guess not :frowning:
Removing the SerialEventRun() call reduces the interval to about 400ns (~33 cycles.) That still seems a bit longer than I'd hope (the instruction sequence looks "ok"), but it's a lot better.

4

Wow. Thanks for the info. I guessed there was stuff going on that is out of sight. How does one go about removing SerialEventRun()?

5

Apologies for my previous misleading post, for some reason I thought I'd read SPI in there, I'm pretty sure I'd only had one beer :slight_smile: