4.18. Marvell Embedded Business Unit (mvebu)¶
4.18.1. Move of the Register Window¶
When an mvebu SoC comes up the internal registers are mapped at 0xd0000000 in the address space. To make it possible to have more than 3.25 GiB of continuous RAM in Linux this window is moved to 0xf1000000. Unfortunately the register to configure the location of the registers is located in this window, so there is no way to determine the location afterwards.
4.18.2. RAM initialisation¶
Traditionally the RAM initialisation happens with a binary blob that have to be extracted from the vendor U-Boot:
scripts/kwbimage -x -i /dev/mtdblock0 -o .
This creates among others a file “binary.0” that has to be put into the board directory. For license reasons this is usually not included in the barebox repository.
Note that in the meantime U-Boot has open source code to do the RAM initialisation that could be taken.
4.18.3. Booting second stage¶
Since v2017.04.0 barebox can boot a barebox image even if the register
window is moved. This is implemented by writing the actual window position
into the image where it is then picked up by the second stage bootloader.
4.18.4. Booting from UART¶
The mvebu SoCs support booting from UART. For this there is a tool available in
barebox called kwboot. Quite some mvebu boards are reset once more when
they already started to read the first block of the image to boot which
obviously results in a failure to boot this image. If you want to boot such a
board, use the parameter -n 15 for kwboot to delay uploading the image
and try to hit the right (i.e. second) window harder.
(The number might have to be adapted per board. The semantic is that the magic
string is sent until the 15th NAK is seen and only then the image is sent.) A
typical commandline is:
kwboot -b barebox.img -n 15 -B 115200 -t /dev/ttyUSB
4.18.5. mvebu boards¶
Not all supported boards have a description here.
