Running Zephyr real-time operating system (RTOS) on ARM® Cortex®-A or Cortex-M cores is a well-established practice, supported by extensive documentation and examples. However, several processors in the NXP i.MX and i.MX RT families include additional compute engine—one or more Cadence Tensilica digital signal processors (DSPs) cores—designed for high-performance audio, voice and neural network processing.
This blog article will focus on utilizing the Cadence Xtensa HiFi4 DSP, which is most widely used across NXP’s product lineup. However, the concepts and methods described here are also applicable to other Cadence DSPs, which are carefully selected by NXP to give the best power efficiency and performance tradeoffs.
The HiFi4 DSP offloads compute-intensive workloads from the main ARM cores, improving overall system performance and energy efficiency. With Zephyr RTOS support, the HiFi4 DSP becomes an accessible, open and highly flexible platform for embedded developers targeting heterogeneous NXP applications.
The NXP i.MX 8M Plus is a representative example of a heterogeneous architecture, integrating:
Similarly, several devices in the i.MX RT crossover microcontroller unit (MCU) family also include a HiFi4 DSP core, combining microcontroller simplicity with DSP acceleration for advanced real-time and audio processing.
These heterogeneous designs enable workload partitioning according to performance, latency, and power requirements. Linux typically operates on the Cortex-A cores, while Zephyr RTOS runs on the Cortex-M core. Zephyr can also be deployed on the HiFi4 DSP for signal or data processing tasks.
The DSP is optimized for:
By offloading such functions to the DSP, systems can achieve higher responsiveness, reduced CPU load and lower energy consumption.
The Zephyr Project is an open source, scalable RTOS optimized for embedded and heterogeneous environments. It supports multiple hardware architectures while providing a consistent, modular framework for device drivers, IPC and synchronization.
NXP has contributed extensions to Zephyr RTOS to enable HiFi4 DSP support across both i.MX and i.MX RT product families. These enhancements make it easier for developers, and the wider community, to take full advantage of DSP acceleration in mixed-core systems.
Supported platforms include:
| Device Family | Zephyr Target Board |
|---|---|
| i.MX 8M Plus | imx8mp_evk/mimx8ml8/adsp |
| i.MX 8QuadMax | imx8qm_mek/mimx8qm6/adsp |
| i.MX 8QuadXPlus | imx8qxp_mek/mimx8qx6/adsp |
| i.MX 8ULP | imx8ulp_evk/mimx8ud7/adsp |
| i.MX RT600 | mimxrt685_evk/mimxrt685s/hifi4 |
| i.MX RT700 | mimxrt700_evk/mimxrt798s/hifi4 |
Additionally, on some i.MX RT targets, we have other DSPs such as HiFi1 or Fusion F1.
| Device Family | Zephyr Target Board |
|---|---|
| i.MX RT500 | mimxrt595_evk/mimxrt595s/f1 |
| i.MX RT700 | mimxrt700_evk/mimxrt798s/hifi1 |
The same Zephyr build environment can be used for all of these targets, allowing a unified development workflow across ARM and DSP cores.
Firmware loading and runtime management are handled by the Linux remoteproc driver (on i.MX platforms) or multicore management frameworks (on i.MX RT platforms), while OpenAMP provides robust intercore messaging.
The Zephyr project offers a variety of examples that demonstrate its capabilities—from basic system bring-up to advanced processing and intercore communication. The following sections will walk you through several examples that demonstrate how to use Zephyr on the HiFi4 DSP.
The standard Zephyr hello_world sample demonstrates successful boot and execution of Zephyr on the HiFi4 DSP. Once the firmware is built and loaded, the DSP console output confirms successful startup:
This sample establishes a foundation for more advanced applications involving inter-processor communication and workload offloading.
The number_crunching example highlights the computational advantages of the HiFi4 DSP. This sample performs vector operations, fast Fourier transform (FFT) and filtering using either the Cortex microcontroller software interface standard–digital signal processing (CMSIS-DSP) backend or the highly optimized Cadence NatureDSP library.
Execution cycle counts demonstrate the significant efficiency gains achieved by the NatureDSP backend, particularly for FFT and infinite impulse response (IIR) filter routines. These performance advantages make the HiFi4 DSP ideal for tasks such as audio post-processing, beamforming and real-time data filtering.
Many applications benefit from collaboration between the ARM and DSP cores. The openamp_rsc_table sample demonstrates how Zephyr running on the HiFi4 DSP communicates with Linux running on an ARM core, using OpenAMP and Remote Processor Messaging (RPMsg). This enables reliable and low-latency message passing between heterogeneous cores.
For example, imagine a mixed-OS multicore system where a Cortex-A core runs Linux while the HiFi4 DSP runs Zephyr. Linux can handle user-space interfaces and high-level control, while the DSP executes computational tasks under Zephyr RTOS, exchanging data in real time through shared memory.
For advanced audio applications, SOF builds on Zephyr RTOS to provide a complete open source audio processing framework on the HiFi4 DSP.
SOF enables professional-grade, low-latency audio pipelines, fully integrated with Advanced Linux Sound Architecture (ALSA) on Cortex-A platforms. It supports:
This framework demonstrates how Zephyr enables scalable, production-ready DSP solutions for i.MX product line.
Experience seamless DSP acceleration in your NXP designs. Get started with Zephyr RTOS on HiFi4—review our sample projects now .
Running Zephyr RTOS on the HiFi4 DSP provides multiple benefits:
The Cadence HiFi4 DSP integrated in NXP i.MX and i.MX RT processors is a high-performance, low-power compute engine well suited for signal processing, audio and AI acceleration. Through Zephyr RTOS support, this DSP becomes an integral part of a unified, heterogeneous processing environment.
From basic Zephyr examples such as hello_world, to performance-oriented number-crunching routines and complex intercore communication with OpenAMP, Zephyr on the HiFi4 DSP delivers a scalable foundation for innovation. Together with SOF, this capability extends to production-ready audio pipelines and advanced embedded workloads, offering flexibility and openness across the NXP ecosystem.
Zephyr RTOS enables the HiFi4 DSP to operate as a powerful coprocessor—unlocking new performance and efficiency opportunities for next-generation of embedded designs.
Iuliana is a Software Engineer at NXP, working primarily on Zephyr, along with Sound Open Firmware and Linux Audio Subsystems. She’s passionate about exploring new technologies, driving innovation and improvements in everyday work. Iuliana enjoys connecting with people, sharing knowledge, and turning ideas into impactful results.