AT91Bootstrap is the 2nd level bootloader for Atmel AT91 SoC providing a set of algorithms to manage the hardware initialization such as clock speed configuration, PIO settings, DDR2 DRAM initialization. After that it downloads your main application, usually the Linux Kernel image, from the first microSD partition to DDR2 RAM main memory and runs it from there.

The binary executable file of AT91Bootstrap must be stored in the first FAT32 partition of the bootable SD card with the name boot.bin.

At startup is RomBOOT (the 1st levet booloader saved in the CPU ROM) that searches and loads boot.bin from microSD card to the 32KB SRAM located inside the CPU itself and runs it from there.

How to compile AT91Bootstrap:

Install the cross compiler and the toolchain required on your Linux Ubuntu PC following this article (Tested on Ubuntu 13.10):

Copy the CORE9G25 AT91Bootstrap from the CD to the tmp folder, then do the follow command to uncompress it:

~$ cd ~
~$ tar xvf /tmp/at91bootstrap.tar.bz2 -C .

This is a fork of the original Atmel version available on GitHub.

Move inside the at91bootstrap directory and launch Make:

~$ cd at91bootstrap
~/at91bootstrap$ make mrproper
~/at91bootstrap$ make at91ariag25sd_linux_dt_defconfig

Now let's change the configuration by typing:

~/at91boostrap$ make menuconfig

make menuconfig screenshot

For example it is possible to change the command line to pass to the Linux Kernel image by selecting:

Linux Image Storage Setup -->
   Linux kernel parameters 

Then change the DRAM memory size by changing the line:

mem=256M console=ttyS0,115200 root=/dev/mmcblk0p2 rootfstype=ext4 rootdelay=1


mem=128M console=ttyS0,115200 root=/dev/mmcblk0p2 rootfstype=ext4 rootdelay=1

When the configuration in ready save and launch the compilation by typing:

~/at91boostrap$ make

Copy the binary file generated on the first partition of SD card and rename it in boot.bin:

~/at91bootstrap$ cp binaries/at91ariag25-sdcardboot-linux-dt-3.5.3-acme-1.1.bin /media/$USER/kernel/boot.bin

If you are using an Ubuntu release older than 13.10 remove $USER in the path

A compiled version of AT91Bootstrap is available on:

Related links

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