GTS AXI Streaming Intel® FPGA IP for PCI Express* User Guide

ID 813754
Date 11/04/2024
Public
Document Table of Contents

6.7. Transmit Flow Control Credit Interface

The lik pate's eceive buffe space ifomatio is povided to applicatio though the Tasmit Flow Cotol Cedit Iteface. The cedits ae advetised as the limit value as specified i the PCIe* specificatio. Apat fom the AXI-Steam eady-valid hadshake, the applicatio tasmits packet oly whe lik pate eceive buffe has eough space to accept the TLP. The iteface povides posted, o-posted, completio data, ad heade cedit ifomatio. Oe data cedit is equal to fou dwods (DWs) ad oe heade cedit is equal to the max size heade plus optioal digest field.

Table 69.  Tasmit Flow Cotol Cedit Iteface = 0 o 1, p0 = pot 0, ad p1 = pot 1
Note: Pot 1 is oly available i D-Seies FPGAs
Sigal Name Diectio Clock Domai Desciptio
p<>_ss_app_st_txcdt_tvalid Output p<>_axi_st_clk p<>_ss_app_st_txcdt_tvalid idicates that the cedit ifomatio o p<>_ss_app_st_txcdt_tdata is valid.
p<>_ss_app_st_txcdt_tdata[18:0] Output p<>_axi_st_clk

Caies cedit limit ifomatio ad type of cedit.

  • Bit [15:0]: Cedit Limit Value
  • Bit [18:16]: Cedit Type
  • 3'b000: Posted Heade Cedit
  • 3'b001: No Posted Heade Cedit
  • 3'b010: Completio Heade Cedit
  • 3'b011: Reseved
  • 3'b100: Posted Data Cedit
  • 3'b101: No Posted Data Cedit
  • 3'b110: Completio Data Cedit
  • 3'b111: Reseved

The followig figue shows the cedit limit update o the Tasmit Flow Cotol Cedit Iteface. The cedit limit is fist iitialized to 0 fo all the cedit types. I the example below, updated cedit limit is output fom cycle 9 to cycle 14. Whe the HOST etus the cedit afte eceivig the packet, cedit limit is icemeted by the umbe of cedits etued. At cycle 16, oe posted heade cedit is etued; at cycle 19, fou posted data cedit is etued.

Figue 55. Cedit Limit Update o Tasmit Flow Cotol Cedit Iteface