In order to support programing and debugging AVR devices over the same interface as ARM-based devices, three vendor commands are used. Commands are send using the AVR_CMD vendor command. All commands are synchronous and result in one and only one response. The response is, however, buffered on the tool and must be polled for using the AVR_RSP vendor command. Events occur asynchronously to commands, and must be periodically polled for using the AVR_EVT vendor command.
The AVR command set is described in AVR Communication Protocol.