IPR-PCIE/8 Altera, IPR-PCIE/8 Datasheet - Page 52

• Manufacturer Part Number: IPR-PCIE/8
• Description: IP CORE Renewal Of IP-PCIE/8
• Manufacturer: Altera
• Type: MegaCorer

Specifications of IPR-PCIE/8

• Software Application: IP CORE, Interface And Protocols, PCI
• Supported Families: Arria GX, Cyclone II, HardCopy II, Stratix II
• Core Architecture: FPGA
• Core Sub-architecture: Arria, Cyclone, Stratix
• Rohs Compliant: NA
• Function: PCI Express Compiler, x8 Link Width
• License: Renewal License
• Lead Free Status / RoHS Status: na
• Lead Free Status / RoHS Status: na

Functional Description
3–14
PCI Express Compiler User Guide
5.
6.
7.
To allow the Write Requester in the above description to transmit packets
continuously, the Credit Allocated and the Credit Limit counters must be
initialized with sufficient credits to allow multiple TLPs to be transmitted
while waiting for the FC Update DLLP that corresponds to freeing of the
credits from the very first TLP transmitted.
The value in the Credit Allocated register is used to create an FC
Update DLLP.
After an FC Update DLLP is created, it arbitrates for access to the
PCI Express Link. The FC Update DLLPs are typically scheduled
with a low priority. This means that a continuous stream of
Application Layer TLPs or other DLLPs (such as ACKs) can delay
the FC Update DLLP for a long time. To prevent starving the
attached transmitter, FC Update DLLPs are raised to a high priority
under three circumstances:
a.
b.
c.
After arbitrating the FC Update DLLP to be the next item
transmitted, in the worst case, the FC Update DLLP may need to wait
for a currently being transmitted maximum sized TLP to complete
before it can be sent.
The FC Update DLLP is received back at the original Write
Requester and the Credit Limit value is updated. If there were
packets stalled waiting for credits, they now can be transmitted.
PCI Express Compiler Version 6.1
When the Last Sent Credit Allocated counter minus the amount
of received data is less than a Max Sized Payload and the
current Credit Allocated counter is greater than the Last Sent
Credit Counter. Essentially, this means the Data Sink knows the
Data Source has less than a full Max Payload worth of credits,
and therefore is starving.
When an internal timer expires from the time the last FC
Update DLLP was sent, which is configured to 30 us to meet the
PCI Express specification for resending FC Update DLLPs.
When the Credit Allocated counter minus the Last Sent Credit
Allocated counter is greater than or equal to 25% of the total
credits available in the Rx Buffer, then the FC Update DLLP
request is raised to High Priority.
Altera Corporation
December 2006