TBD Installing U-Boot to the STM32H7 SOM (uClinux) explains how to install the U-Boot firmware to the board for the first time. Having installed U-Boot, U-Boot is immediately available on the STM32H7 SOM as a primary firmware monitor.

The default U-Boot configuration is a capable Linux bootloader so typically our customers do not require re-building and re-installing U-Boot. However, certain projects still do require customizations to the U-Boot firmware, which implies making changes to the U-Boot code, rebuilding the U-Boot binary and then updating it on the STM32H7 SOM.

1. Building U-Boot

The full U-Boot source for the Emcraft STM32H7 SOM board is included in the software distribution available from the Emcraft web site. Refer to the u-boot/ sub-directory in the software distribution tree.

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1. On the Linux development host, activate the cross-build environment as described in TBD Installing and activating cross development environmentActivating Cross Development Environment (uClinux) :

   Code Block
   $ . ./ACTIVATE.sh

2. Change to the U-Boot top directory:

   Code Block
   $ cd u-boot

3. Configure U-Boot for the Emcraft STM32H7 SOM board:

   Code Block
   $ make distclean $ make stm32h7_som_nor_defconfig

4. Run make to create the u-boot.img binary:

   Code Block
   $ make -s

2. Upgrading U-Boot "Proper" via Ethernet

The U-Boot command line interface provides a special command that can be used to self-upgrade the U-Boot image on the running target. Before you can run this command, you need to load an upgrade U-Boot binary to the target via Ethernet from a TFTP host, refer to TBD Installing Linux uImage on the STM32H7 SOM for details of the network configuration.

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1. Copy the U-Boot image to the TFTP server, adjust the uboot_image environment variable, if needed:

   Code Block
   STM32H7-SOM U-Boot > printenv uboot_image uboot_image=stm32h7/u-boot.img STM32H7-SOM U-Boot >

2. Download the U-Boot image from the TFTP server and install it to the QSPI Flash:

   Code Block

   STM32H7-SOM U-Boot > run uboot_upgrade ethernet@40028000 Waiting for PHY auto negotiation to complete. done Using ethernet@40028000 device TFTP from server 192.168.0.3; our IP address is 192.168.0.166 Filename 'stm32h7/u-boot.img'. Load address: 0xd0c00000 Loading: ################################################################# ################################ 3.3 MiB/s done Bytes transferred = 495105 (78e01 hex) Erasing 0x00000000 ... 0x000fffff (256 eraseblock(s)) Writing 495105 byte(s) at offset 0x00000000 STM32H7-SOM U-Boot >

3. Verify that the new U-Boot has been successfully installed. Reset the SOM by pressing the S3 button on the carrier board and confirm that the U-Boot has been upgraded:

   Code Block
   U-Boot SPL 2019.04- (May 03 2024 - 06:09:05 +0000) Hit 's' key to enter spl shell: Trying to boot from SPI U-Boot 2019.04- (May 03 2024 - 06:09:05 +0000) ...

Note that the self-upgrade sequence is a dangerous operation. You must be sure that you load and install a functional U-Boot image, which is always a tricky thing when you develop customizations to U-Boot. If something goes wrong, you can re-install the release U-Boot image as documented in Installing U-Boot to the STM32H7 SOM (uClinux) .