Datasheet

Interfaces
Intel
®
Xeon
®
Processor C5500/C3500 Series
Datasheet, Volume 1 February 2010
132 Order Number: 323103-001
Every PCI Express device tracks the above six credit types for both itself and the
interfacing device. The rules governing flow control are described in the PCI Express
Base Specification, Revision 2.0 .
Note: The credit advertisement in Table 76 does not necessarily imply the number of
outstanding requests to memory.
A pool of credits are allocated between the ports based on their partitioning. For
example, the NPRH credit pool is, say, N for the x8 port. If this port is partitioned as
two x4 ports, the credits advertised are N/2 per port.
The credit advertisement for downstream requests are described in Table 77.
Table 76. PCI Express Credit Mapping for Inbound Requests
Flow Control
Type
Definition
Initial IIO
Advertisement
Posted Request
Header Credits
(PRH)
Tracks the number of posted requests the agent is capable of
supporting. Each credit accounts for one posted request.
16(x4)
32(x8)
64(x16)
Posted Request
Data Credits
(PRD)
Tracks the number of posted data the agent is capable of
supporting. Each credit accounts for up to 16 bytes of data.
80(x4)
160(x8)
320(x16)
Non-Posted
Request Header
Credits (NPRH)
Tracks the number of non-posted requests the agent is capable
of supporting. Each credit accounts for one non-posted request.
18(x4)
36(x8)
72(x16)
Non-Posted
Request Data
Credits (NPRD)
Tracks the number of non-posted data the agent is capable of
supporting. Each credit accounts for up to 16 bytes of data.
4
Completion
Header Credits
(CPH)
Tracks the number of completion headers the agent is capable
of supporting.
infinite advertized
64 physical
Completion Data
Credits (CPD)
Tracks the number of completion data the agent is capable of
supporting. Each credit accounts for up to 16 bytes of data.
infinite advertized
16 physical
Table 77. PCI Express Credit Mapping for Outbound Requests (Sheet 1 of 2)
Flow Control
Type
Definition
Initial IIO
Advertisement
Posted Request
Header Credits
(PRH)
Tracks the number of posted requests the agent is capable of
supporting. Each credit accounts for one posted request.
4 (x4)
8 (x8)
16 (x16)
Posted Request
Data Credits
(PRD)
Tracks the number of posted data the agent is capable of
supporting. Each credit accounts for up to 16 bytes of data.
8 (x4)
16 (x8)
32 (x16)
Non-Posted
Request Header
Credits (NPRH)
Tracks the number of non-posted requests the agent is capable
of supporting. Each credit accounts for one non-posted request.
4 (x4)
8 (x8)
16 (x16)