PCIe Devices - PLX Technology

PCIe Flow Control
n
Two types of Flow Control (FC) are provided
l
l
At the Transaction layer
– Used to prevent overflow of Receiver buffers and enable
compliance with ordering rules
– Used by Requestor to track queue/buffer space
available in the Agent across the Link and control TLP
injection rate
– The Transaction Layer performs FC accounting
functions for Received TLPs and ‘gates’ TLP
transmissions based on available ‘credits’ for
transmission
At the Data Link Layer
– Exchanges ‘credits’ on the Link in a Data Link Layer
Packet (DLLP) between Transaction Layers at each end
of the link
• This form of FC is transparent to the Transaction Layer
Copyright by Dashcourses, Inc. 2009
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