R-tile Avalon® Streaming Intel® FPGA IP for PCI Express* User Guide

ID 683501
Date 10/06/2021

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Document Table of Contents Avalon® Streaming TX Interface tx_st_ready_o Behavior

The following timing diagram illustrates the behavior of tx_st_ready_o, which is deasserted to pause the data transmission to the Transaction Layer of the R-tile IP for PCIe, and then reasserted. As an example, the timing diagram shows a readyLatency of three cycles. The application deasserts tx_st_valid_i three cycles after tx_st_ready_o is deasserted. Refer to the Avalon® Interface Specifications for a detailed definition of readyLatency.

The maximum latency between the deassertion of tx_st_ready_o and tx_st_valid_i is 16 cycles.

The application must not deassert tx_st_valid_i between tx_st_sop_i and tx_st_eop_i on a ready cycle unless there is backpressure from the R-tile PCIe IP indicated by the deassertion of tx_st_ready_o. For the definition of a ready cycle, refer to the Avalon® Interface Specifications at https://www.intel.com/content/www/us/en/programmable/documentation/nik1412467993397.html.

Note: This is an additional requirement for the R-tile IP for PCIe that is not compliant to the Avalon® -ST standard.
Figure 26.  Avalon® Streaming TX Interface tx_st_ready_o Behavior