Re: wiki page udpates

[Richard Earnshaw <Richard.Earnshaw%eyrie.plus.com@localhost>]

On 06/11/2018 18:46, Michael van Elst wrote:
> gdt%lexort.com@localhost (Greg Troxel) writes:
> 
>> I could use help with some of the questions; feel free to edit or to
>> email me with answers.  Specifically:
> 
>> - what about RPI0 and RPI0W?
> 
> Should work, without wifi of course. You need proper FDT files.
> 
>> - can you use an earmv6hf build to install on RPI2/3?  If so, is there
>>   an included kernel7 and does that use earmv6h or earmv7hf instruction
>>   set?
> 
> Yes. You build a netbsd.img and install it as kernel.img. It's using
> the earmv6hf instruction set.
> 
>> - if you build with eb, does it work?
> 
> No.
> 
>> - do the earm/v4/v5 builds do anyting useful?  (with the understanding
>>   that surely one should use v6 on a RPI1)
> 
> Wouldn't work for RPI.
> 
>> - does earmv7 run faster than earmv6 on a RPI2/3?  How much?
> 
> Not much of a difference.

Really?

Firstly, I'd expect an earmv7 port to default to hw FP, so anything with
FP should be significantly faster (there are FP variants of armv6, but
they were relatively rare (maybe the pi is an exception, I forget).

Secondly, the cache in v7 is PIPT, so there's no need to do any horrible
page colouring/flushing on every context switch; that should make a
notable difference to overall performance.  I think there might have
been other changes to the cache MMU management ops as well to improve
performance.

V7 introduces thumb2 which gives the notable advantage of a significant
code size saving, and thus better cache efficiency on large apps.

Many v7 chips also have Neon SIMD extensions, which can also improve
performance of some key algorithms if run-time detection is supported (I
believe the v7 versions of the Pi have this).

All of the above, however, are based on architecture changes, not
necessarily on what NetBSD does today.  But they should make a big
difference overall if fully exploited.

> 
>> - why the rpi.img vs armv7.img lack of parallel structure?
> 
> ?
> 
>> - why no armv7_inst.img?  Is it becuase you can install an earmv7hf
>>   build on a RPI2/3 with the inst image from an earmv6hf build?
> 
> It's difficult to boot an install image and have no other mass storage to
> install to.
> 
>> - is the sshramdisk section actually still right?
> 
> No idea.
> 
>> - I think there is no documentation or script to update firmware on a
>>   system once installed, other than a cowboy copy of most of /boot from
>>   an unpacked rpi.img.gz or armv7.img.gz.  And that the firmware is not
>>   in the installed filesystem anywhere.  Correct?
> 
> The documentation wouldn't be NetBSD-specific. Otherwise correct.
> 
>> - explain if a netbsd-8 system should have the firmware updated to
>>   match what is in current
> 
> You probably need it for RPI3b+.
> 
>> - usb enumeration with multiple disks (and root on external)??
> 
> There is no well defined order. Easiest method to handle this is to
> use named wedges, in fstab and in cmdline.txt for booting.
> 
>> - pointer to console font changing - or opinions that this is not about
>>   RPI and should just be dropped
> 
> Probably not even relevant for RPI.
> 
>> - how do you tell anita to emulate RPI1 vs 2 vs 3?
>> - what's the command line for qemu?
> 
> 
> Greetings,
>