I did this in the firmware of a VoIP base station. I was informed by the radio firmware guys that a certain kind of request from the host could not be handled

I did this in the firmware of a VoIP base station. I was informed by the radio firmware guys that a certain kind of request from the host could not be handled concurrently by the radio module due to an unchecked conflict over some global piece of memory or whatever. I create a wait-free circular buffer for serializing the requests of that type, where the replies from the previous request would kick down the next one. No mutexes, only atomic compare-swap.