i.MX 7ULP Heterogeneous Architecture and Different Boot Modes

The i.MX 7ULP is an heterogeneous SoC that presents a power domain architecture different than the other i.MX SoCs. In this architecture, both cores have control of the system power and this allows booting in different modes by changing the primary and auxiliary cores according to the power saving strategy.

This post presents the three boot modes supported by i.MX 7ULP and how to boot in each one of them.

Boot modes

• Dual Boot: M4 works as the primary core, loading from QSPI flash and booting A7 as the auxiliary core from eMMC/SD. This is the default boot mode for i.MX 7ULP.

• Low Power Boot: M4 works as the primary core, loading from QSPI flash and booting A7 on demand.

• Single Boot: A7 works as the primary core controlling the whole system and booting M4. This is not the typical boot mode for the i.MX 7ULP.

Source code

The U-Boot source code for i.MX 7ULP can be found at uboot-imx.

$ git clone https://source.codeaurora.org/external/imx/uboot-imx
$ cd uboot-imx
$ git checkout imx_v2017.03_4.9.88_2.0.0_ga

The SDK package for the i.MX 7ULP Cortex-M4 can be found at MCUXpresso.

To learn how to download and build the SDK package for M4, please see this post.

Dual Boot

To boot on Dual Boot (default), make sure that SW1 is set as 1001.

M4 loads from QSPI flash and A7 loads from SD card.

Low Power Boot

To boot on Low Power Boot, make sure that SW1 is set as 101x.

Only M4 boots on this mode and M4 can be programmed to boot A7 if needed (on demand). In this boot mode, the M4 image must be already flashed to QSPI.

Single Boot

To boot on Single Boot, make sure that SW1 is set as 1000.

In this boot mode, the M4 image is loaded from U-Boot. To build the U-Boot image with the M4 content, follow these commands:

• First, copy the the M4 bootable image (.img file) to the uboot-imx directory and rename it to ulp_m4.bin.

$ cp <sdk_dir>/boards/evkmcimx7ulp/demo_apps/power_mode_switch/power_mode_switch.img \
<uboot-imx_dir>/ulp_m4.bin

For details on how to get the bootable image for M4, please see this post.

• Build U-Boot with the following configuration:

$ export ARCH=arm
$ export CROSS_COMPILE=/usr/bin/arm-linux-gnueabi-
$ make mx7ulp_evk_m4boot_defconfig
$ make

This generates u-boot-dtb.imx. Flash it to the SD Card and boot the board. The board will boot on Single Boot.