NXP i.MX93 EVK (Cortex-A55)

Overview

The i.MX93 Evaluation Kit (MCIMX93-EVK board) is a platform designed to show the most commonly used features of the i.MX 93 Applications Processor in a small and low cost package. The MCIMX93-EVK board is an entry-level development board, which helps developers to get familiar with the processor before investing a large amount of resources in more specific designs.

i.MX93 MPU is composed of one cluster of 2x Cortex-A55 cores and a single Cortex®-M33 core. Zephyr OS is ported to run on one of the Cortex®-A55 core.

Board features:
- RAM: 2GB LPDDR4
- Storage:
  - SanDisk 16GB eMMC5.1
  - microSD Socket
- Wireless:
  - Murata Type-2EL (SDIO+UART+SPI) module. It is based on NXP IW612 SoC, which supports dual-band (2.4 GHz /5 GHz) 1x1 Wi-Fi 6, Bluetooth 5.2, and 802.15.4
- USB:
  - Two USB 2.0 Type C connectors
- Ethernet
- PCI-E M.2
- Connectors:
  - 40-Pin Dual Row Header
- LEDs:
  - 1x Power status LED
  - 2x UART LED
- Debug
  - JTAG 20-pin connector
  - MicroUSB for UART debug, two COM ports for A55 and M33

Supported Features

The Zephyr mimx93_evk board configuration supports the following hardware features:

Interface	Controller	Driver/Component
GIC-v4	on-chip	interrupt controller
ARM TIMER	on-chip	system clock
UART	on-chip	serial port

Devices

System Clock

This board configuration uses a system clock frequency of 24 MHz. Cortex-A55 Core runs up to 1.7 GHz.

Serial Port

This board configuration uses a single serial communication channel with the CPU’s UART4.

Programming and Debugging

Copy the compiled zephyr.bin to the first FAT partition of the SD card and plug the SD card into the board. Power it up and stop the u-boot execution at prompt.

Use U-Boot to load and kick zephyr.bin to Cortex-A55 Core1:

fatload mmc 1:1 0xd0000000 zephyr.bin; dcache flush; icache flush; dcache off; icache off; cpu 1 release 0xd0000000

Or use the following command to kick zephyr.bin to Cortex-A55 Core0:

fatload mmc 1:1 0xd0000000 zephyr.bin; dcache flush; icache flush; dcache off; icache off; go 0xd0000000

Use this configuration to run basic Zephyr applications and kernel tests, for example, with the Basic Synchronization sample:

# From the root of the zephyr repository
west build -b mimx93_evk/mimx9352/a55 samples/synchronization
west build -t run

This will build an image with the synchronization sample app, boot it and display the following ram console output:

*** Booting Zephyr OS build zephyr-v3.2.0-8-g1613870534a0  ***
thread_a: Hello World from cpu 0 on mimx93_evk_a55!
thread_b: Hello World from cpu 0 on mimx93_evk_a55!
thread_a: Hello World from cpu 0 on mimx93_evk_a55!
thread_b: Hello World from cpu 0 on mimx93_evk_a55!

References

More information can refer to NXP official website: NXP website.

Using the SOF-specific variant

Purpose

Since this board doesn’t have a DSP, an alternative for people who might be interested in running SOF on this board had to be found. The alternative consists of running SOF on an A55 core using Jailhouse as a way to “take away” one A55 core from Linux and assign it to Zephyr with SOF.

What is Jailhouse?

Jailhouse is a light-weight hypervisor that allows the partitioning of hardware resources. For more details on how this is done and, generally, about Jailhouse, please see: 1, 2 and 3. The GitHub repo can be found here.

How does it work?

Firstly, we need to explain a few Jailhouse concepts that will be referred to later on:

Cell: refers to a set of hardware resources that the OS assigned to this cell can utilize.
Root cell: refers to the cell in which Linux is running. This is the main cell which will contain all the hardware resources that Linux will utilize and will be used to assign resources to the inmates. The inmates CANNOT use resources such as the CPU that haven’t been assigned to the root cell.
Inmate: refers to any other OS that runs alongside Linux. The resources an inmate will use are taken from the root cell (the cell Linux is running in).

SOF+Zephyr will run as an inmate, alongside Linux, on core 1 of the board. This means that said core will be taken away from Linux and will only be utilized by Zephyr.

The hypervisor restricts inmate’s/root’s access to certain hardware resources using the second-stage translation table which is based on the memory regions described in the configuration files. Please consider the following scenario:

Root cell wants to use the UART which let’s say has its registers mapped in the [0x0 - 0x42000000] region. If the inmate wants to use the same UART for some reason then we’d need to also add this region to inmate’s configuration file and add the JAILHOUSE_MEM_ROOTSHARED flag. This flag means that the inmate is allowed to share this region with the root. If this region is not set in the inmate’s configuration file and Zephyr (running as an inmate here) tries to access this region this will result in a second stage translation fault.

Notes:

Linux and Zephyr are not aware that they are running alongside each other. They will only be aware of the cores they have been assigned through the config files (there’s a config file for the root and one for each inmate).

Architecture overview

The architecture overview can be found at this location. (latest status update as of now and the only one containing diagrams).

How to use this board?

This board has been designed for SOF so it’s only intended to be used with SOF.

TODO: document the SOF build process for this board. For now, the support for i.MX93 is still in review and has yet to merged on SOF side.