ARM boot process

[M. Warner Losh]

In message: <44FDAE15.1010400 at freebsd.org>
            Andre Oppermann <andre at freebsd.org> writes:
: M. Warner Losh wrote:
: > In message: <44FC3626.701 at freebsd.org>
: >             Andre Oppermann <andre at freebsd.org> writes:
: > : I'm new to the embedded system world and have got some Atmel
: > : at91rm9200 eval boards I'm playing with.  Most of them came
: > : with Linux and some boot loader to it.
: > : 
: > : The supplied boot loaders can't load a FreeBSD arm kernel and
: > : complain about wrong magic.
: > 
: > Which kernel were you using?
: 
: After I sent the original email I tried a couple of things and got
: some help on developers IRC as well (missing you there lately).
: 
: What I did was to check out the arm tree from p4 and do a 'make
: TARGET_ARCH=arm kernel-toolchain' followed by a 'make TARGET_ARCH=
: arm KERNCONF=KB920X buildkernel'.  The KB920X is modified such that
: it includes the hints.at91rm9200.  One step I somehow did but can't
: reproduce today was the 'make trampoline' target.  Every time and way
: I try it now fails in elf_trampoline.c because it doesn't have proper
: sys/* includes as seen from the kernel compile directory.  There I'm
: stuck right now.  The kernel from yesterday successfully boots on the
: KB9202 and mounts root over NFS.  The loader is the super-primitive
: one that comes with the board.  I'm setting mac, ip and tftp server
: address, do the tftp download to 0x20000000 and start from that address.

OK.

: What I've got no clue yet is how to build a MFS image that gets fused
: with the kernel so I may skip NFS and boot with only TFTP or even put
: it on flash.

I've done that, but I'll have to check my notes.  I've use mkfs to
creaet the ramdisk image, and then frobbed some knob in the config
file to included when I built kernel.tramp.

: > boot0* is to bootstrap the board.  boot0 lets you load an arbitrary
: > program to execute.  boot0iic allows you to load an image to put in
: > the iic eeprom (maybe on only on the KB9202).  boot0spi allows you to
: > load an image into the SPI part.
: > 
: > bootiic is usually what you put in the iic part to boot.  It's fully
: > functional.  If you have different eeprom parts, you'll need to tweak
: > it.
: 
: OK, this looks pretty much like the Kwikbyte loader.

Except that it works... :-)  There's lots of bugs in the kwikbyte
loader.

: > bootspi is what I put in the SPI part.  It is presently optimized for
: > the part that I have, and might need some tweaks.
: > 
: > bootsd will boot off a SD card.  It doesn't quite work yet, there's
: > some unaligned accesses that I'm still working on sorting out...
: 
: SD is the interesting part.  ;-)
: 
: I included the qdmmc driver in my working kernel as well but it fails
: to detect an inserted SD (1GB) or MMC (16MB) card.  How does the IO pin
: setup on the AT91RM9200 work?  Where are the IOs assigned to the functions?

Chances are good that the I/O stuff isn't configured correctly.  We're
getting close to the point of needing different I/O config for
different boards.  All that's done right now in kb920x_machdep.c.  In
an ideal world, the boot loader would pass us a board type (I think it
may already), we'd save it (which we don't right now) and then use it
later to do board specific things.

: > : For the at91rm9200 a number of boot loaders are in boot/arm/
: > : but so far I haven't figured out which one to use.  Eventually
: > : I'd like to have it boot from the SD card.
: > 
: > That's not yet in the tree.  I'm working on booting off a UFS
: > partition.
: 
: Perfect.
: 
: > I've not looked at integrating the SD support with things like redboot
: > or uboot yet.
: 
: What does boot2 do?  And how can I boot an ARM kernel w/o doing the
: trampoline step?  Is that possible at all?

boot2 doesn't do anything.  bootsd is a copy of boot2 that's been
augmented to be the only stage.

I don't think that we've investigated getting /boot/loader working
on the arm.  With that, we'd not need the trampoline stuff at all.
That's there to trick the kernel into thinking it was booted with
/boot/loader.

My bootsd code won't care...

I'm not sure what this has to do with redboot or uboot support.  There
I think one would have to boot off a ext2fs partition.

: Once I'm up to speed and familiar with ARM/AT91RM9200 I'm ready to help
: on improving it.  The devices/ports I'll primarily care about and will
: use are SPI, TWI, 8bit parallel bus, SD/MMC, SSC, EMAC.

Same for us, except not parallel bus.

Warner