RTEMS on ARMv8

[Jeff Kubascik]

On 3/28/2019 8:00 AM, Sebastian Huber wrote:
> Hello Jeff,
> 
> On 27/03/2019 19:11, Jeff Kubascik wrote:
>> Hello,
>>
>> I am interested in porting RTEMS to run as a Xen guest on our distro for the
>> Xilinx Zynq UltraScale+ MPSoC. The MPSoC has an ARM Cortex-A53 processor, which
>> is based on the ARMv8 architecture.
>>
>> I have noticed that RTEMS already runs on a few Zynq 7000 boards. However, those
>> are using the Cortex-A9 processor, which is based on the ARMv7 architecture.
>> Looking at the source code, I didn't see any ARMv8 cpu code.
>>
>> I was curious if there has been any work done to port RTEMS to an ARMv8 based
>> platform?
> 
> AArch64 is a completely new architecture port. I think nobody is working
> on that. We may work on AArch32 support for the Zynq UltraScale+ this year:
> 
> http://devel.rtems.org/ticket/3682
> 
> --
> Sebastian Huber, embedded brains GmbH
> 
> Address : Dornierstr. 4, D-82178 Puchheim, Germany
> Phone   : +49 89 189 47 41-16
> Fax     : +49 89 189 47 41-09
> E-Mail  : sebastian.huber at embedded-brains.de
> PGP     : Public key available on request.
> 
> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
> 

Sebastian,

We were able to hack up the xilinx-zynq BSP to get it running on the Ultra96 in
AArch32 mode. Surprisingly, it didn't require too many code changes. Our key
findings were

- Set the CP15BEN bit in the SCTLR register to enable legacy memory barrier
system instructions. This is used in the arm-cp15 cache operations.
- Clear the TRE bit in the SCTLR register to disable TEX remap. This was causing
the page table attributes to show up as strongly ordered, resulting in an
unaligned memory exceptions in the newlib memcpy.
- Update peripheral addresses, IRQs, clock rates to match the MPSoC.
- Update the MMU peripheral region mappings.
- Change the system clock source to clock-generic-timer.
- Change the cache implementation to cache-cp15.

With the above changes, we are able to run all the applications under the
testsuites/samples directory on the Ultra96 via JTAG boot.

Over the weekend, I started putting together a new xilinx-zynqmp BSP layer to
support the Xilinx UltraScale+ MPSoC platform, including the Ultra96 development
board. If the RTEMS community is interested in these patches, we are looking to
submit them later in the week.

-Jeff Kubascik