UCOSII OSTimeGet not accurate relative to time_rtc

Rabbit
1

I am trying to use the timing withing uCOS-II as my real time source.

I only need to service a routine 1x/sec, and this routine takes 100uS to complete.

I seem to be getting innacurate timing. My service routine (which is the higherst priority task) only runs every 1.000- 1.03 seconds.

I have disabled all external interrupts, I run no other interrupts on timers etc. I use OS_ENTER_CRITICAL, but only for some floating point assignments to global variables (infrequent).

I am using an RCM4200

My RTC seems to accurately reflect the true time, so it seems that some periodic interrupts are not being seen by uCOS-II?

Can anyone make any suggestions?

2

Some quick testing seems to reveal that both ethe ADC driver, as well as the SPI driver are the cause of the dropped periodic interrupt servicing.

When I disable both tasks that perform the above, the timing is exact to 5 decimal places. Enabling either task results in timing errors of up to 3% (slower - ie missed interupts).

Is there anything that can be done about this - not very Real Time as it now stands

3

I may be off base but I think OS time is dependent on the number number of ticks per second which defaults to 64. Altering the number of ticks per second may be an avenue to explore.

4

OS Time is by default 64 ticks per second. I was using 256, but decreased it to the default 64 as part of my testing, this had no effect. I do not want to decrease the time slice period further as then response time may be affected by some of the other tasks (Modbus, as well as TCP I/O).

Note that allowing TCP / Modbus does not cause accuracy problems, just the SPI routines (? are interrupts being disabled for a short period, and are they being missed)

5

Problem solved.

I had a few debugging printf (to stdio) in the program to look at runtime A/D and thermocouple outputs.

When eliminating the stdio output, the accuracy is back to 6 decimal places.

The SPI was not the problem.

6

Do me a favor and look at my posting a few down in the thread. I was no help to you but maybe can shed some light on my problem.