TMS320F28069M: Temperature behaviour

Please clarify what you mean by "CPU load diverging". The “T” parts are rated for operation up to 105’C. You should not see any change in the behavior of the device up to the rated temperature.

It seems that CPU is downclocking or something similar. Is there any similar mechanism in the processor ?

We are using external crystal... Do you have any idea ?

We worked hard today and verified that as soon as the chip temperature is above 90°C, the CPU load increases a lot and the execution timings are not respected anymore. 

OK, that shouldn’t be happening. Please try the following:

First ensure that your code has indeed switched to the external crystal. You could do this by the following, especially if your crystal is also 10 MHz, thereby making it difficult to ascertain if the device is indeed running with the external crystal: Write an extreme value in the coarse trim register of INTOSC1, thereby deliberately creating a large deviation from the nominal 10 MHz oscillator frequency. You can now differentiate between INTOSC1 operation and external crystal operation. 

Please enable XCLKOUT option and measure the XCLKOUT frequency, both under normal and erroneous conditions. This is the MOST conclusive proof of the operating frequency.  

I presume code is running off flash without the debug probe (like XDS100) connected. Please double-check if the flash wait-states are correctly configured. You could also program a simple GPIO toggling code in flash and see if the toggling frequency changes with temperature.

Please attach scope plots for all experiments.