What is the diffrence between STM trace and ETM trace? please tell me some usecase ?
STM or ITM are both software driven trace sources (in effect, an optimised/dedicated UART). In Cortex-M, there is an extra layer of hardware trace which does some way to compensating for the absence of performance monitor counters in the smaller parts. Access to the STM can be fairly fast, and software can dump a raw payload to a specific channel. This is a lower overhead than a UART (and the bandwidth should be arranged to permit streamiung writes without worrying about handshaking. Capture for this trace is often built into low end tools.