Arria® 10 and Cyclone® 10 GX Avalon® Memory-Mapped (Avalon-MM) Interface for PCI Express* User Guide

ID 683724
Date 9/10/2024
Public
Document Table of Contents

12.2. Autonomous Mode

Autonomous mode allows the PCIe IP core to operate before the device enters user mode, while the core is being configured.

Intel’s FPGA devices always receive the configuration bits for the periphery image first, then for the core fabric image. After the core image configures, the device enters user mode. In autonomous mode, the hard IP for PCI Express begins operation when the periphery configuration completes, before it enters user mode.

In autonomous mode, after completing link training, the Hard IP for PCI Express responds to Configuration Requests from the host with a Configuration Request Retry Status (CRRS). Autonomous mode is when you must meet the 100 ms PCIe wake-up time.

The hard IP for PCIe responds with CRRS under the following conditions:

  • Before the core fabric is programmed when you enable autonomous mode.
  • Before the core fabric is programmed when you enable initialization of the core fabric using the PCIe link.

All PCIe IP cores on a device can operate in autonomous mode. However, only the bottom Hard IP for PCI Express on either side can satisfy the 100 ms PCIe wake up time requirement. Transceiver calibration begins with the bottom PCIe IP core on each side of the device. Consequently, this IP core has a faster wake up time.

Note: If you enable the autonomous mode for the Hard IP for PCI Express, and also want to enable the Configuration Bypass feature, your design may not be able to link up to Gen 3 speed following a Cold Reset. In this case, a workaround is to configure the whole FPGA, then do a Warm Reset to allow the link to train to Gen 3 speed. Your design, including the autonomous Hard IP for PCI Express and Configuration Bypass, can then run at Gen 3 speed.

Arria V, Cyclone V, Stratix V, Arria® 10 and Cyclone® 10 GX devices are the first to offer autonomous mode. In earlier devices, the PCI Express Hard IP Core exits reset only after full FPGA configuration.