Hello Donald,
On 23-09-14 05:03, Donald Dade wrote:
I recently bought a Jetson TK1 with the intent of learning all about ARM
board bring up; essentially everything that happens between the reset
vector and the spawning of the init process (in Linux). I've got a good
understanding of this for x86, and I'd like to similarly understand what
happens with an ARM SoC.
I've been having a rough go of it, for example I cannot even find in
explicit terms what the reset vector address is. I began to think that
maybe I'm presupposing too many x86 artifacts and that that's not at all
how ARM works. x86 has a lot of cruft left over from the 70s, after all.
So I know that there is a u-boot port for the Jetson, so I cloned the
source, started swimming through it, and quickly started to drown :)
So, my questions are these:
Can anyone briefly explain how the build system works, i.e. how the source
is configured to build for Jetson
The supported boards have a defconfig file in /configs nowadays. In your
case it is jetson-tk1_defconfig. (or ./MAKEALL -l arm | grep jetson)
# build
export CROSS_COMPILE=arm-linux-gnueabi-
make jetson-tk1_defconfig
make all
You should end up with two binaries, spl/u-boot-spl.bin and u-boot.bin.
The former loads the latter one. spl is build from the same sources tree
but the object files are placed in the spl directory (and tweaked for
size).
and how I find where u-boot's entry point is,
- Look at the output to see which start.S is compiled.
- find start.o
- objdump the obtained elf file (with the .bin) and search for reset
There is no universal memory map / startup sequence for ARM if that is
what you were looking for. You need google or a datasheet to figure out
how (might depend on gpio e.g.) and where code execution begins on
the target.
Note versatileqemu_defconfig can be run with qemu / gdb, so you can
just step through it. You need to load symbols for the location u-boot
relocates itself to as well. Google knows how to do that.
so I can just look at what it does?
A small note. There are two "boards" at the moment for ARM, if grep
points you to arch/arm/lib/board.c ignore it since this boards uses
common/board_f.c / common/board_r.c.
Good luck,
Regards,
Jeroen
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