I am using the RSTC_SR register for detecting and logging the type of reset for later diagnosis. However it would appear that when the brownout detector and reset is enabled, the AT91SAM7X256 always reports the brownout reset after power up instead of reporting the power up reset. Has anyone else had this problem or is there a way around it, whether it be in hardware or firmware?

Particularly interesting are resets that indicate an error condition such as watchdog resets. However the brownout reset is also a kind of error condition because if a client complains of strange behaviour and we find that his power supply is often browning out, that can be an indication of where the problems are coming from. Therefore it is helpful to tell the difference between a clean power up and a brown out.

One thing to look at is your power. When applying power if it is dirty or too slow to come up it could show up as brownout reset.

http://www.atmel.com/dyn/resources/prod_documents/doc6260.pdf
"VVDDIN SLOPE (TSLOPE) must be superior or equal to 6V/ms."

Regards,

Thanks for the information. We did check TSLOPE on VDDCORE and are confident that it is acceptable.

I would like to know if it is actually possible to detect a power up reset if the brown out reset and detector is enabled. It seems to me that the brownout reset is always going to activate on power up because the voltage will go through the range where the brownout reset activates. Or am I wrong about this?

Hmm.... I've got a product on my bench (AT91SAM7X) that has the Brown Out reset and dectector enabled. I am able to see a Power Up Reset... and I can see a Brown Out Reset if I fiddle with the power supply.

So it is possible then.

I don't suppose you did anything special other than to follow the guidelines in the document you posted earlier? I also guess you're just reading the RSTC_SR register and not doing anything else in firmware? Not that one can do much in firmware before the micro has actually started executing code...

We also just tried abruptly connecting the power supply rather than letting it power up but again, only a brown out reset is detected. We do have about 2000 - 3000 uF of capacitors around the board on the 3.3V supply so perhaps this is slowing it enough. Have you experienced problems with these sorts of capacitances on the power supply?

Correct.



Sorry, I don't recall ever placing this size capacitor on the 3.3V supply. Our caps are typically around 10uF on the 3.3V supply.

For what its worth our automotive application power supply consists of the following.
12VDC -> RBO08 (reverse battery protection) -> LM2676 5V switcher -> TPS73633DRB 3.3V -> VDDIN

Regards,