Synchronization and Arbitration in Digital Systems

7

Synchronizers in Systems

The function of a synchronizer is to re-time the data passing from one digital processor (the sender) to another (the receiver), so that it can be correctly interpreted by the receiver. This is only necessary when the sender and receiver are independently timed and even then only when their relative timing is unpredictable. For many systems on silicon it is difficult to provide a common clock at a high frequency with low skew, so independent clocks are used for each processor. Even if the clock frequency is nominally the same for both sender and receiver in some cases the requirement to re-use processors and IP blocks in new designs or different fabrication processes will often mean the actual clock frequency in any future implementation may not even be known.

7.1 LATENCY AND THROUGHPUT

A very general synchronizing interface is shown in Figure 7.1 which allows for re-timing as the data as well as some simple flow control to ensure that the data rates on both sides of the interface are matched. Each separately timed data item is accompanied by a write data available signal from the sender which indicates that it valid data is present. Since the data available signal originates from the sender it must be synchronized to the receiver clock before it can be recognized. The receiver then transfers the data to an internal register when it is ready, and signals back to the sender that it is safe to send another data item by means of the ‘read done’ signal. Because ...