Hello,
I was hoping to hear your opinion about a serious problem I have - it is either I solve it or reduce my LPC2478 CPU speed from 72[MHz] to 64[MHz] (11% loss. The problem does not seem to be occurring at lower MHz settings). I posted about this in the past but it was a long time ago. When I place a controller in an environmental chamber and increase the temperature to 80+ Celsius degrees, I often see data abort exceptions, and sometimes I get the impression that the PC takes a hike (even the firmware LED that blinks every 1 second becomes irregular for a while before it stops). The program is launched by a boot loader and has a lower level supporting firmware layer that handles some interrupts (not all). I also see that if RTX is not started at all (but the application hangs in a "for (;;)" loop instead, hence the bootloader and firmware layer were/are involved, but the application is idle) - the system never crashes! I have excluded, as far as I could tell, the roll of external memory or RTX in this situation. However, I still suspect RTX a little (even though my test programs never crashed). My question: did you ever encounter such a situation? Where do I look best? can this be the result of a misbehaving peripheral? NXP have confirmed the LPC2478 is not the reason.
The CPU load will affect the power consumed by the processor which will affect the additional heating internally. It will add extra stress to both processor and power supply.
Caching of memory will both affect CPU load, but also memory timing. If the supply voltage isn't stable or is slightly changing, or the oscillator is jittering or slightly changing frequency, the safety margins can be reduced.
If the chip is running with DRAM, then the refresh needs will be higher at high temperatures but the RAM access patterns can hide the refresh problem. Caching of RAM will change the access pattern and hence change the amount of refresh from normal access cycles. At room temperature, the DRAM refresh may be several times too slow without any problems possible to see because the much slower self-discharge at room temperature.
Per,
thanks. I tried refining the parameters of the DRAM according to the data sheet - it is speced to work until 85 degrees, to no avail. but the DRAM is a suspect, as it seems to make a difference if I cool only that component...