HyperTransport™ System Architecture

The Purpose Of Ordering Rules

Some of the important reasons for enforcing ordering rules on packets moving through HyperTransport include the following:

Maintain Data Coherency

If transactions are in some way dependent on each other, a method is required to assure that they complete in a deterministic way. For example, if Device A performs a write transaction targeting main memory and then follows it with a read request targeting the same location, what data will the read transaction return? HyperTransport ordering seeks to make such events predictable (deterministic) and to match the intent of the programmer. Note that, compared to a shared bus such as PCI, HyperTransport transaction ordering is complicated somewhat by point-to-point connections ...