3. Data Path > Transaction Management
23
PEB383 User Manual
July 25, 2011
Integrated Device Technology, Inc.
Confidential - NDA Required
Figure 8: Downstream Data Path
3.2
Transaction Management
The following sub-sections describe how the PEB383 handles upstream and downstream transactions.
3.2.1
Upstream Transaction Management
Transactions that originate on the PCI Interface that are destined for the PCIe Interface are stored in the
respective queues or buffers in the PCI clock domain, and are then forwarded to the PCIe Core (see
). PCI buffer logic decomposes the received transactions as per the PCIe constraints (for
example, MAX_RD_SIZE, MAX_PAY_SIZE, RCB, and 4-KB address boundary). Three sets of data
and control signals for the three types of transactions (posted, non-posted, and completions) are used
between the PCI and PCIe Cores.
Transactions are stored temporarily in the PCIe Core buffers before they are used to construct TLPs,
and are then made visible to TLP arbiter. The TLPs are processed by the TLP arbiter only after
ordering rules are satisfied. The TLP arbiter selects one of the five input TLPs (error message, PME
message, posted, completion, and non-posted TLPs) in a round-robin mode if sufficient credits and
retry buffer space is available for the specific TLPs. The TLP arbiter continues to check the available
credit and retry buffer space against each of the active inputs, and selects the one that meets the
constraint. The ECRC adder calculates and appends a 32-bit ECRC value to the end of the TLP
selected by the arbiter if ECRC generation is enabled by software, and then forwards the TLP to the
Data link layer.
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LCRC
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Packet
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Address
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ECRC
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TLP
Error
Detecter
Reques t
Generator
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Posted Buf fer
(512 Bytes )
Non-Posted Queue
4 Entries
Upstream Read
Completion Buffer
(1 KB)
PCIe Core
PCI Co re
Receiv e Flo w
Contr ol B uffer s
Delayed Completion
Devi ce Co re Interface