Re: Basic bare metal ARM domain interface

[Julien Grall <julien.grall@arm.com>]

On 25/05/16 20:42, Ivan Pavić2 wrote:
> Hello,

Hello Ivan,

> I'm working on bare metal application for ARM Cortex A7/15 on Odroid XU3
> platform. I'm using Xen 4.6.
>
> After successfully creating bare metal example(by successful I mean I've stuck
> processor in while loop in main function), I probably should initialize memory
> management unit and similiar. I've found FreeRTOS project on Github where
> similiar stuff was done for ARM Cortex A15. Project is done for Xen 4.4.
> Xen FreeRTOS project: https://github.com/GaloisInc/FreeRTOS-Xen/ .
>
> 1) I'm using 4.6. so I don't know if code from  is fully compatible? (I had to
> comment out lot of things because they block program, printing for example)

If I remember correctly, FreeRTOS is not using the device-tree to find 
where reside the GIC MMIO regions (and possible other MMIOs).

The memory layout has been reworked between Xen 4.4 and Xen 4.5. So you 
will need to update the base address hardcoded in FreeRTOS.

I have CCed, Jonathan who did the FreeRTOS port for Xen. He will be able 
to give you more details about it.

>
> 2) Additionally , I would like to implement basic serial output to dom0 from my
> bare metal domU. What is the minimum one should do for implementing console
> output?

We provide a PV console interface. The backend is already implement in 
dom0 (assuming you are using Linux). For the frontend, you can give a 
look, how mini-os [1] has implemented it.

>
> 3) Furthermore, as this should be bare metal application, I would like at least
> to be able to toggle LED. How can interface hardware from domU? My first guess
> would be to directly address Exynos 5422 GPIO registers but I don't know if
> that would work beacause application is running on VCPU (probably not??) ??

By default, the guest has no access to the hardware. You will need to 
specify in the configure file the list of MMIO regions the guest is 
allowed to access. You can find more details about it here [2].

>
> Any answer, example of implementation, specific documentation or advice would
> be very helpful.

There were a few talks to explain how to port an OS on XEN:
  - 
https://events.linuxfoundation.org/sites/events/files/slides/FreeRTOSXenSummit_0.pdf
  - http://fr.slideshare.net/xen_com_mgr/bsdcan-2015-how-to-port-your-bsd

I hope this will help you to create your bare metal app. Feel free to 
send an e-email if you have more questions.

Regards,

[1] 
http://xenbits.xen.org/gitweb/?p=mini-os.git;a=tree;f=console;h=61f51490a1aefc15148b6e1f016d9e63bbfe61aa;hb=HEAD
[2] https://events.linuxfoundation.org/sites/events/files/slides/talk_5.pdf

-- 
Julien Grall

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