A technique for exporting trace data over high-speed serial links

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Overview

MIPI High-Speed Trace Interface (MIPI HTISM) is a serial implementation of the data port, taking advantage of available high-speed serial interface technology used in interfaces such as PCI Express®, DisplayPort™, HDMI® or USB to provide higher transmit bandwidth with fewer I/O pins compared with a parallel implementation. Unlike protocol specifications in the MIPI Gigabit Debug portfolio such as MIPI Gigabit Debug for IPS, HTI is not designed to be used over the high-level protocols implemented by interfaces such as PCI Express, but is intended to reuse the low-level physical high-speed portions of those interfaces in a bare-metal environment.

HTI defines a method to transport a single stream of trace information over a channel consisting of one to eight high-speed serial lanes, using the Aurora 8B/10B protocol (Aurora 8B/10B Protocol Specification, SP002 v2.3). HTI uses the serial simplex mode of Aurora to transmit data in one direction from a target system to a debug test system.

The HTI specification supports transmission of either the MIPI System Trace Protocol (STP)  or MIPI Trace Wrapper Protocol (TWP) over an HTI channel.

The HTI specification consists of the following aspects:

  • The LINK layer, which defines how the trace is packaged into the Aurora 8B/10B protocol
  • The PHY layer, which defines the electrical and clocking characteristics
  • A programmer's model for controlling HTI and providing status information

In addition to the trace information, the HTI LINK layer provides the ability to include:

  • Optional CRC data, to assist in detecting errors in the trace transmission
  • Optional User Flow Control messages, to indicate additional information about the trace data stream

MIPI HTI was developed by the MIPI Debug Working Group and was originally released in July 2016. The most recent version of the specification, HTI v1.1, released in September 2021, introduces electrical enhancements to address more stringent signal-integrity requirements of link rates beyond 12.5 Gigabits per second (Gbps). These include requiring transmitter equalization, adjusting jitter generation and adding programming values for PHY clock frequencies at the higher link speeds.

All MIPI debug and trace specifications, including MIPI HTI, are available for download and use by the public and the open-source community. Members of the MIPI Alliance enjoy benefits such as access to relevant licenses, and opportunities to participate in development activities, interoperability workshops and other events. For information about MIPI Alliance membership, visit Join MIPI.