B&R Industries X20 System, User Manual

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X20 system modules • Digital signal processing modules • X20DS1928
1442 X20 system User's Manual 3.10
4.16.5.10.10.5 "Forward" function example on the X2X bus
The "Forward" function is a method that can be used to substantially increase the FlatStream data rate. The basic
principle is also used in other technical areas such as "pipelining" for microprocessors.
How it works
Communication on the X2X bus cycles through five different steps to transfer a FlatStream sequence. A successful
sequence transfer therefore requires at least five bus cycles.
Step I Step II Step III Step IV Step V
Actions Transfer sequence from
transmit array,
increase Sequence-
Counter
Cyclic matching of MTU and
module buffer
Append sequence
toreceive array,
adjust SequenceAck
Cyclic matching
of MTU and module buffer
Check SequenceAck
Resource Transmitter
(task for sending)
Bus system
(direction 1)
Receiver
(task for receiving)
Bus system
(direction 2)
Transmitter
(task for Ack checking)
Sequence 1
Sequence 2
Sequence 3
Step I Step II Step III Step IV Step V
. . .
Step I Step II Step III Step IV Step V
Time
Time
Sequence 1
Sequence 2
Sequence 3
Step I Step II Step III Step IV Step V
Step I Step II Step III Step IV Step V
Step I Step II Step III Step IV Step V
Bus cycle 1 Bus cycle 2 Bus cycle 3 Bus cycle 4 Bus cycle 5 Bus cycle 6 Bus cycle 7 Bus cycle 8 Bus cycle 9 Bus cycle 10
Bus cycle 1 Bus cycle 2 Bus cycle 3 Bus cycle 4 Bus cycle 5 Bus cycle 6 Bus cycle 7 Bus cycle 8 Bus cycle 9 Bus cycle 10
Figure 449: Comparison of transmission without/with "Forward"
Each of the five steps (tasks) requires different resources. If the Forward function is not used, the sequences are
executed one after the other. Each resource is then only active if it is needed for the current sub-action.
With Forward, a resource that has executed its task can already be working on the next message. The condition
for enabling the MTU has been changed to allow for this. Now the sequences are passed to the MTU based on
timing. The transmitting station no longer waits for an acknowledgment from SequenceAck, which means that the
given bandwidth can be used much more efficiently.
In the most ideal situation, all resources are working during each bus cycle. The receiver still has to acknowledge
every sequence received. Only when SequenceAck has been changed and checked by the transmitter is the
sequence considered as having been transferred successfully.