LVDS Tunneling Protocol and Interface (LTPI) IP User Guide: Agilex™ 3 and Agilex™ 5 FPGAs and SoCs

ID 844310
Date 8/15/2025
Public
Document Table of Contents

1.4.1. Interface Tunneling Principle

The LTPI uses the following generic methods to capture and tunnel various LTPI channels:
  • Sampling—The I/O states are sampled by LTPI and the samples are tunneled in the LTPI frames.
  • Event/State detection—The set of events or states are identified for the channel and sent in LTPI frames based on the interface state.
  • Random access read/writes requests—Random access memory mapped channel is triggered by external interface.
During operational state, channel interface supported by the LTPI IP can be categorize based on whether the RX and TX directions need to be synchronized for tunneling:
  • Asynchronous—For a given channel and interface or link LTPI TX and RX paths are independent.
  • Synchronous—For a given channel and interface or link LTPI TX and RX paths need to be synchronized to allow interface to work correctly after tunneling.
Table 12.  LTPI
Channel Capture Method TX and RX Synchronization Channel Characteristics
GPIO Sampling Asynchronous
  • Captured signal levels are transmitted directly through LTPI.
  • Low latency (LL) GPIOs are updated in every LTPI frame.
  • Normal latency (NL) GPIOs are split across multiple frames with frame ID/frame - counter used to identify the NL GPIO subset.
UART
  • Captured signal levels are transmitted directly through LTPI.
  • UART signals are oversampled.
  • Multiple samples are tunneled in every LTPI frame.
I2C/SMBus Event/State detection Synchronous
  • I2C/SMBus states are encoded into LTPI events and these events are tunneled through LTPI.
  • I2C clock stretching is used while waiting for synchronization to be completed after event is transmitted and waiting for the I2C/SMBus state/event from the other side of the LTPI interface.
Data bus Random access
  • Data bus transaction such as data read and write are encoded into the LTPI events.
  • Completion indication of the bus operation is used to synchronize access to the data bus.