Why do the blue user LED is off and the red user LED is on before main runs? I would expect both of the them to be off, so the user can turn them on according to their application.
In this video between minute 15-16, we can see how the red one is on and the blue off.
Thank you.
Jose,
Thanks for the question and for the nice video.
What you're seeing is the difference in speed between the code and the I/O pin. When an I/O pin changes state it takes a finite amount of time for the pin voltage to change from one logic state to another. The instructions used in your code compile to "atomic" read-modify-write" instructions, which first read the pin state, perform a logical AND on the result, then write the result back. When you perform two of these in quick succession the pin timing comes into effect because the instruction time is faster then the pin. You can read more about it on this Wiki page:
The solution is to separate the two instructions with NOPs, like this:
asm(" NOP");
...or use the GPIO SET/CLEAR/TOGGLE registers instead of writing directly to the DAT register.
I hope this helps.
Regards,
Richard
