System and method for tracking messages between a processing unit and an external device

摘要

An apparatus which uses channel counters in combination with channel count read instructions as a means of providing information that data in a given channel is valid or has not been previously read. The counter may also, in the situation of the channel being defined as blocking, be used to prevent the unintentional overwriting of data in a register used by the channel or, alternatively, prevent further communications with the device assigned to that channel when a given count occurs. Intelligent external devices may also use channel count read instructions sent to the counting mechanism for reading from and writing to the channel.