Zedboard hardware design for Linux

Hello,

As you noted any support for the Digilent version of LInux will need to come from Digilent. That said, here are a couple of links that might be helpful:

https://embeddedcentric.com/customized-hardware-design-and-integration/

https://forums.xilinx.com/t5/Embedded-Development-Tools/Zedboard-oled/td-p/507957

https://ez.analog.com/thread/73996

http://stackoverflow.com/questions/29322127/oled-on-zedboard

http://zedboard.org/content/oled-zed-board

http://zedboard.org/content/zedboard-oled

-Gary

Thanks for the reply!
I already saw most of the links you provided. But most of those designs uses dedicated logic for OLED, and that is not what I want to do.
I would like to connect OLED to GPIO pins of PS in a way to be able to use Digilent OLED driver.

But forget it for now. I decided to maybe go for something simpler. Now I just want to boot Linux on simplest possible design, without anything connected to PL, using as much as I can from OOB design. As far as I know it should be possible, because kernel should boot on slightly different hardware, if I provide proper device tree.

I made hardware design in following way:
1. New Vivado project
2. New Block Design
3. Added Zynq processing system, and customised it with preset for Zedboard
4. Turned off AXI master port connected to PL (no need for it, and compiler complains about not connected clock, if I don't turn it off)
5. Generated bitstream, exported hardware, launched SDK

Then next steps were as follows:
6. Generated device tree, as in tutorial from this link
http://www.wiki.xilinx.com/Build+Device+Tree+Blob
In bootargs I wrote
"console=ttyPS0,115200 root=/dev/ram rw initrd=0x800000,8M earlyprintk rootfstype=ext4 rootwait devtmpfs.mount=0"
And I also changed line
compatible = "xlnx,zynq-7000";
to
compatible = "xlnx,zynq-zed";
because it complains about I think incompatible processor, or system.
7. Generated .dtb file with dtc compiler from Ubuntu repository
8. Generated FSBL as described in
http://www.wiki.xilinx.com/Build+FSBL
9. Generated boot.bin with SDK tool - first added FSBL from (8), then added bitstream from Vivado, then added u-boot from Zedboard OOB files.
10. To finish, I put 4 files to SD card formatted as fat32: bin.boot from (9), devicetree_ramdisk.dtb from (6), Linux image from OOB, and file system image from OOB.

When I tried to boot this, it starts booting, but stops after line "turn off boot console earlycon0" What I am doing wrong, does my plan had any sense? I think I just made something wromg with device tree, but don't know what.

Hi saleksin,

I think what you are trying to do makes sense.  However, keep in mind that the OOB image from Digilent is much older than the tools you are likely using today and it is possible that you are running into compatibility issues between your generated device tree and the older kernel image (possibly even the older U-Boot also).  Speaking of which, you mentioned that you were using Vivado but did not mention which version you are one.

Here you be me suggestion for you, start with one of the Xilinx Linux releases (there are files included for ZedBoard):

http://www.wiki.xilinx.com/Zynq+Releases

Here is one for 2015.4 tools if that is what version you are using:

http://www.wiki.xilinx.com/Zynq+2015.4+Release

First make sure that the Xilinx provided files will boot your ZedBoard just fine.  After that, I would recommend making changes to the following pieces using your own version (in this order) one at a time so that if something does break along the way you have some idea of where it is breaking.

1) FSBL
2) Bitstream
3) Devicetree
4) Linux Kernel (if you want to)
5) U-Boot (if you want to)
6) Root Filesystem

I know it seems like slow progress but at least you will be on a path that can be more easily tackled with a divide and conquer approach.

Try that approach and see if you get some better results.

Regards,

-Kevin

Thanks a lot!

I managed to boot Linux for Zedboard (2016.1) with my FSBL, bitstream, and devicetree. Your tip was very good - device tree for OOB design is completely different than mine, and this from 2016.1 is very similar.

I may be wrong, but AFAIR FSBL depends on hardware design (or at least Zynq config, which is part of it), and also device tree depends on hd, so if I want to change FSBL, I have to change also bistream and devicetree. Am I right?

In device tree I set bootargs for value [00], which I found in original devtree from Linux package. What does this value mean, why Linux started with no bootargs?

And for other people than may see this - it is very important to set properly serial console in device tree - most problems I had was caused by this.

Hi saleksin,

That is great to hear that you are making some progress!  Thank you for reporting back to the community!

You are correct, the FSBL depends upon the HW definition from which SDK derives the ps7_init.* files built into the FSBL.

You need to make changes to the device tree only where you are changing the hardware that the kernel needs to be aware of.  This is because the device tree is providing information to the kernel drivers on the memory location (and configuration) of those hardware peripherals.

Along similar lines, the bitstream can change without updating FSBL or device tree if you are touching Programmable Logic which is not connected to one of the AXI ports.  However, if you are changing AXI connected HW in the bitstream (like add/remove/relocate hardware in memory space) then yes it is fair to say that the bitstream and device tree should change at the same time.

I am not sure about the devicetree entry "bootargs = [00];" since that appears to be new in the 2016.1 release and was not like that in the 2015.4 release.  Perhaps that is a question best asked to the Xilinx forums instead?

Regards,

-Kevin

I asked about [00] on Xilinx forum, and I will post the answer here.

Going back to the beginning - I managed to create proper hardware design, and I want to use oled driver from Xilinx. But it seems it is not in the file image from 2016.1 file image. Can you confirm that? It it is really not there, Is there a possibility to add new kernel module without recompiling whole kernel? I'm trying to keep it simple.

Hi saleksin,

I am not familiar with a ZedBoard OLED driver from Xilinx.  The only one that I am aware of is the one from Digilent.  I think the latest version of that is here and you should be able to compile this as a kernel module.

Here is the Digilent resource center link where you can find the project downloads with source code used for the ZedBoard OOB design:

https://reference.digilentinc.com/zedboard:zedboard

Regards,

-Kevin

Thanks again for the respond.
Now to finish this topic - few days ago, after a few days of trials an errors I managed to compile Linux with this Digilent driver (I meant that one, when I wrote about Xilinx one), but I had to compile it together with whole kernel, not as a module. When I tried to make module from it, compilation failed.
I will try to compile it as module, and I will report if I succeed.
And going back to this strange [00] from dev tree - on Xilinx forum they said that it effect of decompilation of dtb, and it means that it was empty string in original dts.

In case someone will need it in the future - the best reference hardware design can be found on Analog Devices Github repo.

https://github.com/analogdevicesinc/hdl

Manual: https://wiki.analog.com/resources/fpga/docs/hdl

Where is a project called adv7511 which has not only hdmi, but also almost all other peripherials (including audio, gpio, oled).

Instruction on building Linux on it: https://wiki.analog.com/resources/tools-software/linux-drivers/platforms/zynq