Porting FreeBSD to Raspberry Pi

[Mark Tinguely]

On 11/4/2011 11:02 AM, Lev Serebryakov wrote:
> Hello, Arnaud.
> You wrote 4 ноября 2011 г., 19:48:29:
>
>>>> $89, 700MHz Cortex A8, 256MB DRR2, micro-SD. However, do not expect
>>>> being able to run FreeBSD on it before a few years :)
>>>   What is so special about A8?
>>>
>> It is the consumer technology of today. The best people can afford
>> without being in ARM's R&D centers.
>> Let me tell you what is going to happen. ARM11 has been around for
>> years, it will take you a year or two to complete the project, nice,
>> hacker thrill, you did it. However, by the time you release it, the
>> Raspberry Pi will be sold-out and will be replaced by an ARMv7 core,
>> smaller, faster, eventually cheaper. By that time, the current
>> technology will be a 64bits MP-core ARMv8, And you will be in the
>> exact same situation as today, FreeBSD lagging one or two generation
>> behind Linux, keep up.


I am sure people will be running ARM9 (ARMv5) for a long time. Your 
point that they will not be available as consumer products is well taken.


>    As I'm not a ARM specialist, I have several questions.
>
>    Does porting to ARM11 (ARVv6, am I right?) will make porting to
> ARMv7 (Cortex) easier? You see, i486 adds some nice commands, tricks
> and configuration registers to i386, but porting to i486 after you
> have working port to i386/Protected mode is almost trivial.
>    Or it is completely different architectures, which doesn't have
> anything in common?
>
>    ARMvX is only a core, as far as I understand. How much different are
> implementations from different vendors? MMU? Bus? Configuration space?

We can run ARMv6/ARMv7using the ARMv5 model. But it would not be very 
efficient. The ARMv6/7 new features can improve how things run. For 
example we have hardware assisted atomic commands, we can remove all the 
VIVT cache fixing code, and we can share the kernel address space in 
each memory map.

But IMO, there are enough new features in the ARMv7 that finally make 
something pv_entrys un-necessary.

The Cortex-A15 will be out next year with a whole new memory model. (40 
bit physical, 32 bit virtual kernel, 40 bit hypervisor virtual). It will 
have an AMBA change that can shed some bus mastering problems.


Besides the core new features, we always have all the different 
peripherals for each SoC...

>
>    Why do you think, porting to different ARMs should go sequentially?
> :) Yes,  we (FreeBSD) doesn't have a lot of resources, but as nobody
> could be forced to do what he don't want, it is better, IMHO, to have
> ARM11 port, that to not have any ARM port at all.
>
>    But I agree, that port to Cortex-A8/A9 looks more interesting :)
>

The Cortex-A9 pandaboard is $174. The Cortex-A8 and A9 have some 
differences, but they are more alike than the ARM11 and the Cortex-A8.

It will be tough to stay current with the hardware advances without some 
kind of sponsorship.

--Mark Tinguely.