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

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ID 817713
Date 5/09/2024
Public
Document Table of Contents
Document Table of Contents x
1. About the GTS AXI Streaming Intel® FPGA IP for PCI Express* Design Example 2. Quick Start Guide 3. Document Revision History for the GTS AXI Streaming Intel® FPGA IP for PCI Express* Design Example User Guide
1. About the GTS AXI Streaming Intel® FPGA IP for PCI Express* Design Example x
1.1. Programmed Input/Output Design Example 1.2. Programmed Input/Output Design Example Functional Description
1.2. Programmed Input/Output Design Example Functional Description x
1.2.1. GTS AXI Streaming IP—Design Under Test (DUT) 1.2.2. PIO Application 1.2.3. On-Chip Memory (MEM) 1.2.4. GTS System PLL Clocks Intel® FPGA IP 1.2.5. GTS Reset Sequencer Intel® FPGA IP 1.2.6. Reset Release Intel® FPGA IP
1.2.2. PIO Application x
1.2.2.1. Scheduler 1.2.2.2. Read Write Module 1.2.2.3. Avalon® Memory-Mapped Interface 1.2.2.4. Completion Module 1.2.2.5. Width Adapter 1.2.2.6. TX Credit Initialization 1.2.2.7. AXI to Avalon® Streaming Interface Adapter
2. Quick Start Guide x
2.1. Directory Structure 2.2. Generating the Design Example 2.3. Simulating the Design Example 2.4. Design Example Simulation Testbench 2.5. Compiling the Design Example
2.3. Simulating the Design Example x
2.3.1. Steps to Run Simulation using VCS* 2.3.2. Steps to Run Simulation using VCS* MX 2.3.3. Steps to Run Simulation using QuestaSim*
2.3.1. Steps to Run Simulation using VCS* x
2.3.1.1. Running VCS* Simulation in Interactive Mode
2.3.2. Steps to Run Simulation using VCS* MX x
2.3.2.1. Running VCS* MX Simulation in Interactive Mode
2.4. Design Example Simulation Testbench x
2.4.1. Test Driver Module 2.4.2. PIO Design Example Testbench
1. About the GTS AXI Streaming Intel® FPGA IP for PCI Express* Design Example
2. Quick Start Guide
3. Document Revision History for the GTS AXI Streaming Intel® FPGA IP for PCI Express* Design Example User Guide

1.2.2.6. TX Credit Initialization

In the GTS AXI Streaming IP, the back pressure mechanism by the PIO is done through the credit system. Therefore, the credit value must be declared during the credit initialization stage.

An initial TX credit value is captured by the CRDT_INIT and is deducted for any TLP sent to the DUT. When the credit reaches zero, the DUT ceases sending further TLP until the credit is returned by the DUT. This block interfaces with the credit signals from the DUT and focus on initializing and return of the TX credit.

For the TX direction, only crdt_init_ack is asserted in the block to complete the initialization stage. The PIO captures the TX credit during the initialization stage which is initiated by the DUT.

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