While working on a disciplined clock, I decided to check the interrupt response times. I was amazed. With the following code, which does not do a lot of work in either the loop or the interrupt service routine, I was able to send interrupts at a 10Khz input rate and see the loop run fine. Much superior performance to what I expected. I enjoy this environment.
//works to 20khz interrupt rate and still services the loop
int state = LOW;
attachInterrupt(0, intin, FALLING);
Serial.println(“through the loop”);
digitalWrite(7,state); //pin 7 toggles at half input frequency