Flow Control Packets
The transmit side of a device reports flow control credit information from its receive buffers to the opposite device. The specification defines three types of Flow Control packets:
Flow Control Init1 �
used to report the size of the Flow Control buffers for a given virtual channel
Flow Control Init2 �
same as Flow Control Init1 except it is used to verify completion of flow control initialization at each end of the link (receiving device ignores flow control credit information)
Flow Control Update �
used to update Credit Limit periodically
Each Flow Control packet contains the header and data flow control credit information for each virtual channel and type of Flow Control packet. The packet fields that carry the header and data Flow Control credits reflect the counter width as discussed in the previous section. Figure 7-4 pictures the format and content of these packets.
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