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Xtensa Developer Guide

Overview

This page contains information on certain aspects when developing for Xtensa-based platforms.

HiFi Audio Engine DSP

The kernel allows threads to use the HiFi Audio Engine DSP registers on boards that support these registers. The kernel only supports the use of the HiFi registers by threads and not ISRs.

Note

Presently, only the Intel ADSP ACE hardware platforms are configured for HiFi support by default.

Concepts

The kernel can be configured for an application to leverage the services provided by the Xtensa HiFi Audio Engine DSP. Three modes of operation are supported, which are described below.

No HiFi registers mode

This mode is used when the application has no threads that use the HiFi registers. It is the kernel’s default HiFi services mode.

Unshared HiFi registers mode

This mode is used when the application has only a single thread that uses the HiFi registers. The HiFi registers are left unchanged whenever a context switch occurs.

Note

The behavior is undefined, if two or more threads attempt to use the HiFi registers, as the kernel does not attempt to detect (nor prevent) multiple threads from using these registers.

Shared HiFi registers mode

This mode is used when the application has two or more threads that use HiFi registers. When enabled, the kernel automatically allows all threads to use the HiFi registers. During each thread context switch, the kernel saves the outgoing thread’s HiFi registers and loads the incoming thread’s HiFi registers, regardless of whether the thread utilizes them or not.

Additional stack space may be required for each thread to account for the extra registers that must be saved.

Configuration Options

The unshared HiFi registers mode is selected when configuration option CONFIG_XTENSA_HIFI_SHARING is disabled but configuration options CONFIG_XTENSA_HIFI3 and/or CONFIG_XTENSA_HIFI4 are enabled.

The shared HiFi registers mode is selected when the configuration option CONFIG_XTENSA_HIFI_SHARING is enabled in addition to configuration options CONFIG_XTENSA_HIFI3 and/or CONFIG_XTENSA_HIFI4. Threads must have sufficient stack space for saving the HiFi register values during context switches as described above.