Altera IP Compiler for PCI Express - Manual (Page 107)

Chapter 5: IP Core Interfaces 5–21
Avalon-ST Interface
August 2014 Altera Corporation IP Compiler for PCI Express User Guide
Figure 5–24 illustrates the timing of the Avalon-ST TX interface. The core can deassert
tx_st_ready to throttle the application which is the source.
Figure 5–25 illustrates the timing of the 64-bit TX interface when the IP Compiler for
PCI Express backpressures the application by deasserting tx_st_ready. Because the
readyLatency
is two cycles, the application deasserts tx_st_valid after two cycles
and holds tx_st_data until two cycles after tx_st_ready is asserted.
Figure 5–24. Avalon-ST TX Interface Timing
Notes to Figure 5–24 :
(1) The maximum allowed response time is 3 clock cycles for the soft IP implementation and 2 clock cycles for the hard IP implementation.
clk
tx_st_ready
tx_st_valid
tx_st_data0[63:0]
tx_st_sop
tx_st_eop
response_time
cycle 1 cycle 2 cycle 3 cycle 4 cycle n . . .
1 2 3 4 5 6 7 8 9 10 11 12 13
Figure 5–25. 64-Bit Transaction Layer Backpressures the Application
coreclkout
tx_st_sop
tx_st_eop
tx_st_ready
tx_st_valid
tx_st_err
tx_st_data[63:0].. . . . . . . . . . .
readyLatency
00. . 00 ... BB... BB ... BBBB0306BBB0305 BB... BB.. BB ... BB ... BB ... BB ... BB....