III.      SYSTEM ON CHIP BUSES; CONSUMER DOMAIN     

A. STBus is an on-chip bus protocol developed by STMicroelectronics, its main applications are set top boxes, ATM networks and digital still cameras. Three different types of the STBus protocol exist, each having a different level of complexity in terms of both performance and implementation. The arbiter in the STBus is called node while the master and slave are called initiator and target respectively. Type (I) is a simple synchronous handshake protocol with limited set of available command types, no pipelining is applied.
Type (I) acts as a request-grant protocol. Only limited operation code and length are supported.
Type (II) This protocol is more efficient than type I as it supports split transactions and adds pipelining features. The transaction set include read/write operation with different sizes (up to 64 bytes) and also specific operations like read-modify-write and swap.
Type (III) This is the most efficient protocol, as it adds support for split transactions, out-of-order executions, and asymmetric communications. The switch or node is a block that arbitrates requests and responses, different kinds of arbitration are possible, including fixed priorities and variable priorities. STBus can be implemented using different bus topologies as single shared bus, full crossbar and partial crossbar.  [8]