LTPI Protocol Support

Computers & Servers

Low Throughput Peripheral Interface

What is LTPI?

LTPI (Low Throughput Peripheral Interface) is an Intel-defined serial bus used for communication between a host processor or BMC and platform peripherals in server and computing platforms. LTPI provides a lightweight, low-pin-count alternative to eSPI for connecting peripherals that do not require high bandwidth, such as GPIO expanders, fan controllers, and basic I/O devices. The interface uses a synchronous clock and data pair, operating at speeds up to 24 MHz. Engineers working on Intel server platform bring-up and debug need LTPI decode capability to verify peripheral enumeration, command/response exchanges, and data transfers between the host and LTPI-attached devices.

LTPI Quick Reference

type Serial, synchronous
signals CLK, DATA
max Speed 24 MHz
voltage Range 1.8V
features Intel platform bus

Acute Instruments Supporting LTPI

TravelLogic Series

TravelLogic Series
LA4000 Series

LA4000 Series

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How to Analyze LTPI with Acute Instruments

1

Connect your Acute logic analyzer to the LTPI CLK and DATA lines on the platform board.

2

Attach a ground lead to the target board's ground reference.

3

In the Acute software, select the LTPI protocol decoder and assign CLK and DATA to the correct input channels.

4

Configure the decoder for the expected bus speed and framing parameters.

5

Capture and view decoded LTPI transactions showing command types, register addresses, and data payloads.

Frequently Asked Questions

What sample rate do I need for LTPI analysis?
LTPI operates at clock speeds up to 24 MHz. For reliable decoding, use a sample rate of at least 100 MHz (approximately 4x the clock frequency). A sample rate of 200 MHz or higher is recommended to clearly resolve clock-data relationships and accurately decode command and data phases.
Why is my LTPI decoder not recognizing transactions?
LTPI decode failures often result from incorrect voltage threshold settings — LTPI signals typically use 1.8V logic levels. Verify that the logic analyzer's input threshold is configured for 1.8V. Also check that both CLK and DATA connections are solid and that the probes are attached at the correct test points on the board. If the platform has not completed initialization, LTPI traffic may not yet be present.
How many channels are needed for LTPI analysis?
LTPI requires 2 channels — CLK and DATA. If you need to monitor additional sideband signals such as reset or interrupt lines, add one channel per signal. For platforms with multiple LTPI buses, allocate 2 channels per bus.

Related Protocols

eSPI SMBus

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