Porting Cora Z7 Board to barebox

Thu May 1 05:16:39 PDT 2025

Hi,

thanks for the fast replies.

Am Tue, Apr 29, 2025 at 11:49:40AM +0200 schrieb Ahmad Fatoum:
> Hi,
> 
> On 4/29/25 10:34, Sascha Hauer wrote:
> > In case of the Zedboard you could take start_avnet_zedboard.pbl. This
> > contains all necessary components including device tree and barebox
> > proper.
> > 
> > However, this binary is linked to 0x0 and the FSBL will likely load it
> > there. I don't know where the FSBL itself is located.

Can I change the address to which barebox is linked to? E.g. in Vitis
the application is linked to 0x10000 and the FSBL starting this
application to 0x0.

> 
> The pbl files tend to be a bit bigger, because they are meant only
> as input to objcopy. You can add to images/Makefile.zynq, e.g.
> 
>   image-$(CONFIG_MACH_ZEDBOARD) += start_avnet_zedboard.elf
> 
> And it will generate a much more compact ELF file that should
> be interchangeable (I had tested this on ZynqMP).
> 
> >> Is there a way to hard code the UART to use for the barebox
> >> console for barebox proper?
> > 
> > Why do you want to hardcode it? Setting the console via device tree is
> > just fine.
> > 
> > For debugging your early code I recommend CONFIG_DEBUG_LL. For zynq the
> > UART is hardcoded to ZYNQ_UART1_BASE_ADDR in include/mach/zynq/debug_ll.h.
> > You can change it in this file.
> > 
> > With CONFIG_DEBUG_LL enabled you can put putc_ll() in your code.
> 
> CONFIG_DEBUG_PBL is also often useful.
> 
> >> The Zynq on the Cora Z7 only embeds a single core Cortex A9 while the SoC on the
> >> Zedboard embeds a dual core Cortex A9. Does this affect the cores initialization
> >> in arch/arm/mach_zynq?
> > 
> > I don't think so. I haven't used Zynq myself though.
> 
> Cheers,
> Ahmad
> 
> > 
> > Regards,
> >   Sascha
> > 
> 
> -- 
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> 

The good news is, I can boot barebox (PBL and proper) now and sometimes
also can Linux. Here is the output of my barebox:

Digilent Cora Z7 PBL
uncompress.c: memory at 0x00000000, size 0x20000000
mmu: enabling MMU, ttb @ 0x1ffd0000
endmem                = 0x20000000
arm_mem_scratch       = 0x1fff8000+0x00008000
arm_mem_stack         = 0x1ffe9000+0x0000f000
arm_mem_ttb           = 0x1ffd0000+0x00010000
arm_mem_barebox_image = 0x1fe00000+0x00200000
arm_mem_early_malloc  = 0x1fde0000+0x00020000
membase               = 0x00000000+0x20000000
uncompress.c: uncompressing barebox binary at 0x00006270 (size 0x00029c0c) to 0x1fe00000 (uncompressed size: 0x0006c0e8)
uncompress.c: jumping to uncompressed image at 0x1fe00000

barebox 2025.04.0-00215-gdacb19ae3252-dirty #11 Wed Apr 30 22:22:15 CEST 2025

Board: Digilent Cora Z7
ERROR: could not get clock /axi/dma-controller at f8003000:apb_pclk(0)
ERROR: could not get clock /axi/etb at f8801000:apb_pclk(0)
ERROR: could not get clock /axi/tpiu at f8803000:apb_pclk(0)
ERROR: could not get clock /axi/funnel at f8804000:apb_pclk(0)
ERROR: could not get clock /axi/ptm at f889c000:apb_pclk(0)
ERROR: could not get clock /axi/ptm at f889d000:apb_pclk(0)
mdio_bus: miibus0: probed
macb e000b000.ethernet at e000b000.of: Cadence GEM at 0xe000b000
arasan-sdhci e0100000.mmc at e0100000.of: registered as mmc0
malloc space: 0x17e00000 -> 0x1fdfffff (size 128 MiB)
arasan-sdhci e0100000.mmc at e0100000.of: error while transferring data for command 6
arasan-sdhci e0100000.mmc at e0100000.of: state = 0x01f70202 , interrupt = 0x00208000
mmc0: Card's startup fails with -74
barebox-environment chosen:environment-sd.of: probe failed: No such file or directory
environment load /dev/env0: No such file or directory
Maybe you have to create the partition.

Do you know what to do about the "could not get clock errors"? Do I have
to take care about them or just ignore them?

The more critical error comes from the SD card. Every second boot I am
getting the errors shown above, sometimes the card is started correctly.

Also when barebox can startup the mmc0, when starting the Linux Kernel
sometimes the rootfs on /dev/mmcblk0p2 is not found and the SD Card is
not detected. So, there seems to be something wrong with the SD Card
interface...

In lowlevel.c I am setting the clock divider for the sdio0 interface to 10
and the Source for generated clock is IO PLL. Therefore, the sdio IP
should get a 100 MHz input clock. IS this correct? Do you know which
clockrate the driver expects? 

Or do you have any other idea what could case the error?

In case I can fix the remaining errors I would like to bring the changes
upstream and send a patch. Here I also have some questions:

I added the following files and folder:

	arch/arm/boards/digilent-cora/
	arch/arm/dts/zynq-cora.dts
	dts/src/arm/xilinx/zynq-cora.dts

arch/arm/boards/digilent-cora/ is a copy of arch/arm/boards/avnet-zed/
with my changes applied. In the Copyright, should I keep the existing
name and just add mine as a second author?

If I understand it correctly, the files in dts/src are imported from the
Linux kernel git repo, right? In this case I should try to bring my
modified device tree mainline to Linux first and then commit my changes
to barebox? Or is there another file location I can drop my device tree
temporarily until it is available in Linux?

And a last question: How can I change the default boot method in barebox
from net to mmc0?

Thanks and best regards,
Johannes