Optimizing The Configuration; Ieee 1394 Data Transfer Protocol - HP E8491B IEEE 1394 Configuration And User's Manual

Optimizing the
Configuration
IEEE 1394
Data Transfer
Protocol
arbitration rest gap
1. Isochronous data transfers broadcast variable amounts of data at regular intervals with no acknowledgement.
Isochronous and Asynchronous data transfers can occur on the same bus.
Chapter 4
I/O performance is impacted slightly by the hardware configuration.The
VXI mainframe closest to the PC (root node) has the highest priority. For
example, if instruments in VXI mainframes 1 and 3 (Figure 4-1) contend for
the bus at the same time, the root node will grant mainframe 1 access to the
bus first. However, the bus's fair arbitration protocol (covered in the next
section) ensures that each device has equal access to the bus and that devices
closer to the root are not continually granted the bus.
Data transfer over the IEEE 1394 bus can be either asynchronous or
1
isochronous . Hewlett-Packard's IEEE 1394 based VXI systems use
asynchronous data transfers and a "fair arbitration" protocol to ensure each
VXI mainframe has equal access to the bus. Figure 4-2 illustrates the
concepts of asynchronous data transfers and fair arbitration.
VXI mainframe 2
data packet
F I n-1
mainframe 1 or 2
arb data
ack
seq packet
subaction 1
Figure 4-2. IEEE 1394 Data Transfer Protocol.
VXI mainframe 1
block transfer
data packet
data packet
Fairness Interval n
mainframe 1 or 2 mainframe 3
arb data arb data
ack
seq packet seq packet
subaction 2 subaction 3
subaction gaps
IEEE 1394 Fundamentals and Interface Overview
VXI mainframe 3
block transfer
data packet
data packet
data packet
F I
n+1
ack
arbitration gap
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