[Xenomai-help] rt_read_timer value

[nourry@domain.hid]

Hi,

i try to make a little program that just records time reaction : a picture
appears and we must press a key. Time between image appeared and keypress is
recorded.

For that, i use rt_time_read() in aperiodic mode (since if we don't specify
rt_task_set_periodic(), aperiodic mode is default, that's right ?).

It seems working until a little bit more 2 seconds, but after that, value
returned is negative and decreasing, while it was positive and increasing (weird
because i've read that in aperiodic mode it should be decreasing all the time).

Moreover, i believe remember that while beginning this program, time was always
decreasing, like real-time task were affected by the rest of the program.

I must record time until 5 seconds after image appeared, and this problem
doesn't ease the task.

I must have made a mistake, can someone help me ?

Another little question, which functions, librairies, calls in one word can we
make in real-time tasks without breaking it ? I want to use event detection from
SDL library to catch keypress, there's a function that polls for events (for the
moment i use kbhit). It doesn't seems to increase latency in an endless loop. I
must keep latency under 1 ms since goal is to measure time reaction with
accuracy.


Thanks to all,
Antoine