cannot serial.print a variable that gets incremented in a ISR

Projects Programming
1

I at the moment trying to print a variable that gets incremented in a ISR.

The serial communication shows a lot of "??" and never once the number i want.. what could be the problem?

speed_profile.cpp
speed_profile.h
main.ino

What am I doing wrong?

Serial.print is not being called from the ISR but The function compute_speed_profile, which compute some init stuff, and then has a thread for it own in which it Serial.print is being called.
the thread has interrupt guards on it.. which should stop interrupt from affecting the serial.print.

The output i receive from the serial monitor is something like this 88xx�8�8�888�88��8�8888�8��

speed_profile.h (2.03 KB)

main.ino (835 Bytes)

speed_profile.cpp (7.09 KB)

2

Are you calling Serial.print from within an ISR? Arduino doesn't like that

Maybe it's something simple like your (crazy) baud rate Serial.begin(230400); do you have that in the monitor?

3

What variables are used in the ISR and in the function? Those variables need to be declared volatile. Otherwise, the compiler assumes that they will not change, and probably throws a lot of your code away.

4

Two obvious problems:

  1. Any variables that are accessed by both interrupt and non-interrupt code must be declared volatile.
  2. Any multi-byte variables that are accessed by both interrupt and non-interrupt code must be read in the non-interrupt code within "interrupt guards":
noInterrupts()
//read variable here, and copy to a tmp variable
interrupts();

And, since you only provided snippets, rather than a complete program, there may well be other problems in the code you didn't show...

Regards,
Ray L.

5

The baudrate is correct (was also my first guess)
I changed all the member variable of speed profile to volatile, and it still doesn't provide me any useable information.

6

I changed all the member variable of speed profile to volatile

Is the instance volatile, too?

7

PaulS:
Is the instance volatile, too?

The only reason why I was only providing snippets and not the whole was to make the problem clearer, and no one would ever dare to read the complete code.
I am using interrupts guards (cli(), and sei()) but i will update the post with the full code.

I just changed the instance, and that didn't work either..:frowning:

(Hate to wait 5 minutes to reply)

9

I attached the full code above

10

This is weird.. I initializes the serial to run on baudrate 9600 but it is only readable on a higher baudrate ?
57600 in this case? why?

11 
cli();
    status_step_count.data = profile.moved_steps;
    Serial.print("profile.moved_steps: ");
    Serial.println(profile.moved_steps);
    Serial.print('\n');
    sei();

Serial printing requires interrupts to be enabled.

cli();
    status_step_count.data = profile.moved_steps;
    sei();
    Serial.print("profile.moved_steps: ");
    Serial.println(profile.moved_steps);
    Serial.print('\n');
12

that makes sense, but as mentioned before does it work on different baudrate, eventhough i initialized it to 9600?

13

57600/9600 = 6. Rats, I was thinking maybe the "divide system clock by 8" fuse bit was incorrect.

14

Ahh.. could have been, but i am using timer1 and not timer0... So