Timer using a single counter to track multiple time-outs

Abstract

A circuit such as a host adapter includes a timer capable of detecting time-outs for multiple pending commands. The timer includes a single free-running counter, a first storage for start counts, a second storage for time-out values, a subtractor, and a comparator. The start counts are counts from the counter that are saved when issuing an associated command. The time-out values indicate the lengths of different types of time-out periods. To check whether a command timed out, a start count associated with the command is selected from the first storage, and the subtractor determines a difference between a current count in the counter and the selected start count. The difference is then compared to a time-out value that is selected from the second storage according to the type of time-out. The command timed out if the difference is greater than the selected time-out value. In one embodiment, the second storage includes count registers for time-out values, a multiplexer, and select register that provides a select signal to the multiplexer. The select register contains a value associated with the command, and the number of count registers matches the number of types of time-outs.