Response handshake rspval and rspack 11142 cells

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: request and response handshakes are independent of each other – Request handshake: CMDVAL and CMDACK – Response handshake: RSPVAL and RSPACK 11/142 Cells, Packets, and Packet Chains Institute of Electronics, National Chiao Tung University • Each handshake transfers a cell across the interface. The cell size is the width of the data passing across a VCI. – 1, 2, 4, 8, or 16 bytes for BVCI – 1, 2, 4, bytes for PVCI • Cell transfers can be combined into packets, which may map onto a burst on a bus. – A VCI operation consists of a request packet and a response packet – Packets are atomic – Packets are similar in concept to “frames” in PCI • Packets can be combined into chains, to allow longer chains of operations to go uninterrupted. 12/142 Request and Response Contents Institute of Electronics, National Chiao Tung University • Request contents are partitioned into three signal groups and validated by the CMDVAL signal – Opcode, specify the nature of the request (read or write) – Packet Length and Chaining – Address and Data • Response contents validated with the RSPVAL. Each request has its response. – Response Error – Read Data 13/142 BVCI Signals CLOCK RESETN Institute of Electronics, National Chiao Tung University System Signals CMDVAL CMDACK Request Handshake ADDRESS[n-1:0] BE[b-1:0 | 0:b-1] CFIXED CLEN[q-1;0] Initiator Request Contents CMD[1:0] CONTIG Target WDATA[8b-1:0] EOP CONST PLEN[k-1:0] WRAP RSPACK Response Handshake RSPVAL RERROR[E:0] Response Contents REOP RDATA[8b-1:0] 14/142 BVCI Protocol Institute of Electronics, National Chiao Tung University • The protocol has three stacked layers: transaction layer, packet layer, and cell layer • Transaction layer: A pair of request and response transfers – Above hardware implementation – A series of communicating objects that can be either hardware or software modules – The information exchanged between initiator and target nodes is in the form of a request-response pair 15/142 Packet Layer Institute of Electronics, National Chiao Tung University • The packet layer adds generic hardware constraints to the system model • In this layer, VCI is a bus-independent interface, just physically point-to-point • A transaction is called a “VCI operation” if the information is exchanged using atomic request and response transfers. In a packet layer, a VCI transaction decomposes into one or more operations. 16/142 Packet Institute of Electronics, National Chiao Tung University • Packet is the basic unit of information that can be exchanged over the VCI in an atomic manner. • Multiple packets can be combined to form larger, non-atomic transfer units called packet chains. • A VCI operation is a single request-response packet pair. • Packet length is the number of bytes transferred • The content of a packet depends on whether it is a request or response packet and the type of operation being carried out - such as read, write, etc. 17/142 Cell Layer Institute of Electro...
View Full Document

This note was uploaded on 08/23/2009 for the course IEE 5016 taught by Professor Tian-sheuanchang during the Spring '05 term at National Chiao Tung University.

Ask a homework question - tutors are online