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Your question is very broad. I am not sure what layer and which side you wanted to understand.
The base IPC mechanism on K3 devices are all through the ti-rpmsg-char library in userspace, which is the interface for the rpmsg-char driver. A C66 would publish an end-point to A72 to create a rpmsg bus device at Linux kernel level. This is done in the appRemoteServiceInit() call using the PDK IPC API RPMessage_create() and RPMessage_announce().
The published rpmsg device on the A72-side will probe the rpmsg-char driver and creates a /dev/rpmsg_ctrlX character device. A userspace application will open a file description (fd) to this character device, and uses the fd to read and write to the remote end-point. appRemoteServiceRun sends a message to an fd corresponding to your remoteproc. These fd is created during the appRemoteServiceInit() call.
