The Optional Executable Image (OEI) is an optional plugin loaded and executed by Cortex-M processor ROM on many NXP i.MX processors. The Cortex-M is the boot core, runs the boot ROM which loads the OEI, and then branches to the OEI. The OEI then configures some aspects of the hardware such as DDR config, init TCM ECC, etc. There could be multiple OEI images in the boot container. After execution of OEI, the processor returns to ROM execution.

Supported development environments include Ubuntu 2020.04, 2022.04, and 2024.04.

Download from GitHub

To download the repo from GitHub, first install git:

sudo apt update
sudo apt -y install git

Then clone the repo:

git clone https://github.com/nxp-imx/imx-oei

Installing the Toolchain

Compiling requires an ARM cross-compiler. Download and install the required arm-none-eabi toolchain from the Arm GNU Toolchain Downloads website. For example, from the x86_64 Linux hosted cross toolchains AArch32 bare-metal target (arm-none-eabi) section, download the *.xz file to a directory for the tool chain (e.g. tools) and then:

tar xvf *.xz

Set the TOOLS shell variable to the directory the toolchain is installed in. For example:

export TOOLS=~/tools

When the toolchain is in a directory like arm-gnu-toolchain-12.3.rel1-x86_64-arm-none-eabi in this tools directory.

Also ensure the Linux installation is up-to-date and then install:

sudo apt -y install make gcc g++-multilib srecord

Compiling an OEI Image

To get started with the OEI on an NXP iMX95 EVK LP5 board, download the GitHub repository and then compile the OEI for the target configuration.

For example to build DDR OEI, in the top directory of the code base (e.g. imx-oei):

make board=mx95lp5 oei=ddr DEBUG=1

Copy the resulting binary image file, build/mx95lp5/ddr/oei-m33-ddr.bin, to the iMX95 directory of the mkimage tool.

Similarly, to build TCM init OEI, in the top directory of the code base (e.g. imx-oei):

make board=mx95lp5 oei=tcm DEBUG=1

Then copy the resulting binary image file, build/mx95lp5/tcm/oei-m33-tcm.bin, to the iMX95 directory of the mkimage tool. Build a boot container using mkimage, program it to the boot device, and boot the board. The OEI will display debug messages on the M33 debug UART of i.MX95 19x19 EVK.

Customers will usually create their own board port that configures the DDR on their board.