The Minimum Flow Control Advertisement

The minimum number of credits that can be reported for the different Flow Control buffer types is listed in Table 7-1 on page 303.

Table 7-1. Required Minimum Flow Control Advertisements

Credit Type	Minimum Advertisement
Posted Request Header (PH)	1 unit. Credit Value = one 4DW HDR + Digest = 5DW.
Posted Request Data (PD)	Largest possible setting of the Max_Payload_Size; for the component divided by FC Unit Size (4DW). Example: If the largest Max_Payload_Size value supported is 1024 bytes, the smallest permitted initial credit value would be 040h.
Non-Posted Request HDR (NPH)	1 unit. Credit Value = one 4 DW HDR + Digest = 5DW.
Non-Posted Request Data (NPD)	1 unit. Credit Value = 4DW.
Completion HDR (CPLH)	1 unit. Credit Value = one 3DW HDR + Digest = 4DW; for Root Complex with peer-to-peer support and Switches. Infinite units. Initial Credit Value = all 0's for Root Complex with no peer-to-peer support and Endpoints.
Completion Data (CPLD)	n units. Value of largest possible setting of Max_Payload_Size or size of largest Read Request (which ever is smaller) divided by FC Unit Size (4DW); for Root Complex with peer-to-peer support and Switches. Infinite units. Initial Credit Value = all 0's; for Root Complex with no peer-to-peer support and Endpoints.