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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
– 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
CMDACK Request Handshake ADDRESS[n-1:0]
BE[b-1:0 | 0:b-1]
Request Contents CMD[1:0]
CONTIG Target WDATA[8b-1:0]
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
– 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
• 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.
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 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,
17/142 Cell Layer
Institute of Electro...
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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.
- Spring '05