Altera HyperTransport MegaCore Function - Manual (Page 51)

Chapter 3: Specifications 3–25
HyperTransport MegaCore Function Specification
© November 2009 Altera Corporation HyperTransport MegaCore Function User Guide
Preliminary
The transmit packets have special handling for the case in which a response or
non-posted packet has the
PassPW bit reset. In this case, the transmit buffers enforce
strict HT requirements. For example, if a response packet that has the PassPW bit
reset is written to the transmit response buffer, the previously written posted packet is
transmitted first. Because it is possible to write to the transmit posted buffer and
transmit response buffer simultaneously, the previously written posted command is
defined as the one that was started on or before the clock cycle preceding the start of
packet of the response packet. The same is true in the case of non-posted packets.
Table 3–8 describes the Tx buffer ordering implemented by the HyperTransport
MegaCore function.
Table 3–8. Tx Buffer Ordering
Row Pass Column Posted Request Non-Posted Request Response
Packet PassPW
Specificaton
(1)
MegaCore
Function
Specification
(1)
MegaCore
Function
Specification
(1)
MegaCore
Function
Posted
Request 1 Yes/No No Yes Yes (2) Yes Yes (2)
0 No
Non-Posted
Request 1 Yes/No Yes (2) Yes/No No Yes/No Yes (2)
0 No No
Response 1 Yes/No Yes (2) Yes Yes (2) Yes/No No
0 No No
Notes to Table 3–8 :
(1) This column indicates the requirements as specified by the HyperTransport I/O Link Specification Revision 1.03.
No—The row request type may not pass the column request type.
Yes—The row request type must be allowed to pass the column request type to avoid deadlock conditions.
Yes/No—The row request type may pass the column request type but there is no requrement to do so.
(2) A “Yes” indicates that the row may pass the column subject to available buffer credits and internal scheduling.