BCM7445 and BCM7260

This document describes how to use U-Boot on the Broadcom 7445 and Broadcom 7260 SoC, as a third stage bootloader loaded by Broadcom’s BOLT bootloader.

BOLT loads U-Boot as a generic ELF binary. Some U-Boot features such as networking are not implemented but other important features are, including:

  • ext4 file system traversal

  • support for loading FIT images

  • advanced scripting

  • support for FIT-provided DTBs instead of relying on the BOLT-provided DTB

A customized version of this port has been used in production. The same approach may work on other BCM7xxx boards, with some configuration adjustments and memory layout experimentation.



$ make bcm7445_defconfig


$ make bcm7260_defconfig


$ make
$ ${CROSS_COMPILE}strip u-boot


To tell U-Boot which serial port to use for its console, set the stdout-path property in the /chosen node of the BOLT-generated device tree. For example:

BOLT> dt add prop chosen stdout-path s serial0:115200n8

Flash the u-boot binary into board storage, then invoke it from BOLT. For example:

BOLT> boot -bsu -elf flash0.u-boot1

This port assumes that I-cache and D-cache are already enabled when U-Boot is entered.

Flattened Image Tree Support

What follows is an example FIT image source file. Build it with:

$ mkimage -f image.its image.itb

Booting the resulting image.itb was tested on BOLT v1.20, with the following kernels:

and with a generic ARMv7 root file system.


/ {
        description = "BCM7445 FIT";
        images {
                kernel@1 {
                        description = "Linux kernel";
                         * This kernel image output format can be
                         * generated with:
                         * make vmlinux
                         * ${CROSS_COMPILE}objcopy -O binary -S vmlinux vmlinux.bin
                         * gzip -9 vmlinux.bin
                         * For stblinux-3.14, the specific Broadcom
                         * board type should be configured in the
                         * kernel, for example CONFIG_BCM7445D0=y.
                        data = /incbin/("<vmlinux.bin.gz>");
                        type = "kernel";
                        arch = "arm";
                        os = "linux";
                        compression = "gzip";
                        load = <0x8000>;
                        entry = <0x8000>;
                        hash@1 {
                                algo = "sha256";
                ramdisk@1 {
                        description = "Initramfs root file system";
                        data = /incbin/("<initramfs.cpio.gz>");
                        type = "ramdisk";
                        arch = "arm";
                        os = "linux";
                        compression = "gzip";
                         * Set the environment variable initrd_high to
                         * 0xffffffff, and set "load" and "entry" here
                         * to 0x0 to keep initramfs in-place and to
                         * accommodate stblinux bmem/CMA reservations.
                        load = <0x0>;
                        entry = <0x0>;
                        hash@1 {
                                algo = "sha256";
                fdt@1 {
                        description = "Device tree dumped from BOLT";
                         * This DTB should be similar to the
                         * BOLT-generated device tree, after BOLT has
                         * done its runtime modifications to it.  For
                         * example, it can be dumped from within
                         * U-Boot (at ${fdtcontroladdr}), after BOLT
                         * has loaded U-Boot.  The result can be added
                         * to the Linux source tree as a .dts file.
                         * To support modifications to the device tree
                         * in-place in U-Boot, add to Linux's
                         * arch/arm/boot/dts/Makefile:
                         * DTC_FLAGS ?= -p 4096
                         * This will leave some padding in the DTB and
                         * thus reserve room for node additions.
                         * Also, set the environment variable fdt_high
                         * to 0xffffffff to keep the DTB in-place and
                         * to accommodate stblinux bmem/CMA
                         * reservations.
                        data = /incbin/("<bolt-<version>.dtb");
                        type = "flat_dt";
                        arch = "arm";
                        compression = "none";
                        hash@1 {
                                algo = "sha256";
        configurations {
                default = "conf@bcm7445";
                conf@bcm7445 {
                        description = "BCM7445 configuration";
                        kernel = "kernel@1";
                        ramdisk = "ramdisk@1";
                        fdt = "fdt@1";