Open Source Summit Europe 2022

The support for HIFI instruction set for Clang unlocks the development of audio components for Sound Open Firmware (SOF). Based on the Esp32 Clang port from Esspresiv, it adds a HIFI instruction set and built-in functions required for optimized DSP codes.

Xtensa DSP technology (owned by Cadence) is the workhorse behind many audio interfaces in PCs and laptops, such as Intel HD Audio, AMD High Definition Audio or Mediatek audio devices. Xtensa processor family consists of a core ISA and several extensions. The most notable extension type is the HIFI instruction family, which unlocks VLIW (Very Long Instruction Word) and SIMD (Single Instruction, Multiple Data) capabilities for DSP codecs. Those DSP algorithms are governed by the Sound Open Firmware standard. However, until now, the work on DSP algorithms has been confined to hardware vendors due to proprietary licensing of the DSP compiler technology.

The presentation contains an overview of the Clang toolchain and a detailed description of features required to port a Clang toolchain to another architecture. Most notably, the work on HIFI extension has to deal with C language extension for vectors. Vector variables are outside of the ISO standard and present various implementation challenges.