Qualcomm/ProcComm

Processor Communications (an implementation of Inter Processor Communications - IPC) on Qualcomm System-on-Chip devices that have a privileged modem (a.k.a. baseband or radio) processor and less privileged applications processor is via shared memory and interrupts.

Devices based on the Qualcomm MSM and QSD SoC designs also use the Qualcomm-provided modem operating system REX and the Advanced Mobile Subscriber Service (AMSS) application running on the privileged processor - usually an ARM9 design.

Proc comm allows the applications processor to do Remote Procedure Calls (RPC) to the modem processor and receive the results in the shared memory (SMEM) channel buffer - just an area of Random Access Memory (RAM) set aside for the purpose.

In analysing devices using proc comm it is possible to determine the RPC calls that can be made since the commands and their arguments are sent as pure text using the sprintf() function. On the modem side sscanf() is used to decode the RPC and translate it into a local function call.