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Chapter : B–17
Descriptor/Data Interface
August 2014 Altera Corporation IP Compiler for PCI Express User Guide
Transaction Examples Using Transmit Signals
This section provides the following examples that illustrate how transaction signals
interact:
Ideal Case Transmission
Transaction Layer Not Ready to Accept Packet
Possible Wait State Insertion
Transmit Request Can Remain Asserted Between Transaction Layer Packets
Priority Given Elsewhere
Transmit Request Can Remain Asserted Between Transaction Layer Packets
Multiple Wait States Throttle Data Transmission
Error Asserted and Transmission Is Nullified
Ideal Case Transmission
In the ideal case, the descriptor and data transfer are independent of each other, and
can even happen simultaneously. Refer to Figure B–12. The IP core transmits a
completion transaction of eight dwords. Address bit 2 is set to 0.
In clock cycle 4, the first data phase is acknowledged at the same time as transfer of
the descriptor.
Figure B–12. TX 64-Bit Completion with Data Transaction of Eight DWORD Waveform
clk
tx_req
tx_ack
tx_desc[127:0]
tx_dfr
tx_dv
tx_data[63:32]
tx_data[31:0]
tx_ws
tx_err
CPLD
DW0
DW1
DW2
DW3
DW4
DW5
DW6
DW7
123456789
Descriptor
Signals
Data
Signals
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