An Evaluation of ACP Collision Resolution Performance

Ford's Audio Control Protocol (ACP) is a UART-based protocol which does not use bitwise arbitration. Instead, software algorithms provide collision avoidance and collision resolution. The collision resolution method is non-deterministic and whether or not all collisions can be resolved within a specified time interval is an important ACP protocol issue.

To focus on this technical issue, an executable mathematical model of ACP's data link layer was constructed to characterize all transmit, receive, and timing elements of the protocol. Given the performance requirement that all collisions must resolve within a specified time interval, this model was used to analyze the protocol's byte-level collision behavior. This paper examines the performance characteristics of ACP's collision resolution algorithm, and recommends improvements.