Compiling AT91bootstrap

AT91bootstrap is the 2nd level bootloader used by the Microchip ARM MPUs to initializate the internal hardware (clocks, peripherals, DDR DRAM, etc) at startup and load the Linux Kernel image from the first microSD partition. This article illustrates how to compile at91bootstrap for the RoadRunner module

Tested with at91bootstrap version 3.9.1

Toolchain installation

First of all you need to install the toolchain (cross compiler, linker, etc) on your Linux Ubuntu PC following this article (tested on Ubuntu 18.04.4 LTS):

Download the latest AT91bootstrap version from Microchip GitHub repository:

The GitHub repository is available here:

Clone this repository in your Linux PC by typing:

git clone https://github.com/linux4sam/at91bootstrap.git
cd at91bootstrap
git checkout tags/v3.9.1

Set the board configuration

Roadrunnermake sama5d2_roadrunner_defconfig
Acqua with 256MB of RAMmake acqua-256m_defconfig
Acqua with 512MB of RAMmake acqua-512m_defconfig
Aria with 128MB of RAMmake aria-128m_defconfig
Aria with 256MB of RAMmake aria-256m_defconfig
Arietta with 128MB of RAMmake arietta-128m_defconfig
Arietta with 256MB of RAMmake arietta-256m_defconfig

Change the default configuration

If you want to take a look to the at91bootstrap configuration run:

make menuconfig

This function could be useful to change for example the Kernel line passed by at91bootstrap to the kernel.

Example: Enable the suspend to RAM

To enable the suspend to RAM features it is request to change the flag Enable Backup Mode e add some parameters on the ckernel command line:

Type:

make menuconfig

Enable this flag:

[*] Enable Backup Mode

Go to:

Kernel Image Storage Setup  --->  

change the line:

mem=256M console=ttyS0,115200 root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait consoleblank=0 

in

mem=256M console=ttyS0,115200 root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait consoleblank=0  atmel.pm_modes=ulp0,backup

Compile and check the command line parameters by typing:

cat /proc/cmdline

Compiling

launch the compilation by typing:

make CROSS_COMPILE=arm-linux-gnueabihf-

it will generate a binary fine in ./binaries directory with a different name for any board type.

A symbolic link is generated automatically during the at91bootstrap compilation so you can refer to it with the name boot.bin.

Copy boot.bin on a bootable MicroSD

If your board boot everything from the MicroSD copy boot.bin on the first microSD partition by typing:

cp binaries/boot.bin /media/$USER/boot

If your are using a Roadrunner be sure that PA30 (MMC1 CD) is wired on GND.

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Sergio Tanzilli
System designer, webmaster and Acme Systems co-founder

Personal email: tanzilli@acmesystems.it
Webpage: https://www.acmesystems.it
Github repositories: https://github.com/tanzilli and https://github.com/acmesystems
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