The High Speed Synchronous Interface (HSI) is one of the Legacy Specifications MIPI issued several months after its creation in 2003.The  HSI working group released its v1.01 specification in 2008 to improve the MIPI Baseband-Application interface solution while maintaining  backward compatibility with HSI 1.0.

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The physical layer described in this document provides improvements to previous version of the HSI physical layer (see [MIPI01]) such as increased serial link efficiency, and potentially pin-count reduction. In addition, designs based on the physical layer described in this document do not require a specific protocol layer, and may implement proprietary protocols, if desired.


This document specifies the physical layer of the High Speed Synchronous Serial Interface (HSI). The objective of this specification is to specify the physical layer signaling so that anybody using this document can implement an IC with a compatible HSI link. The specification also provides enough information about the usage of the interface, so that designers implementing an HSI link can make rational decisions regarding system partitioning and interconnectivity choices inside the SOC.


HSI is an interface designed to connect an application die to a cellular modem die in cellular handsets, but also can be used for other purposes. HSI provides a multi-processor (or more broadly said on-chip-interconnect) low-latency communication channel over a die-to-die link by dividing the physical link to logical channels at the hardware level. HSI enables versatile, easy and simple serial link realizations. As such, HSI can reduce time-to-market and design cost of mobile handsets by simplifying serial die-to-die physical layer implementations.