[maemo-developers] Xsp pixel-doubling solutions for Nokia 770?

[From: Siarhei Siamashka]

On Wednesday 02 May 2007 23:01, Arnim Sauerbier wrote:

> If the memcpy on 770 is something like 190MB/s, pushing 800x480 at 30fps
> would use only 12 percent of that bandwidth

I'm sorry, I was the source of this misleading information, I forgot that
you are a Nokia 770 user and mentioned some numbers from N800.

I measured the memory bandwidth as ~170-190MB/s for memcpy 
and ~410MB/s for memset on N800.

The same numbers on Nokia 770 are ~70-100MB/s for memcpy (depending on
relative source and destination buffers alignment) and ~120MB/s for memset
with the standard glibc functions.

These glibc functions have ARM assembly optimizations developed by Nicolas
Pitre from MontaVista Software, Inc., but according to comments found inside,
they were developed for XScale cpus. Such code is not so good for Nokia 770
and can be replaced with something better.

Using some arm926ej-s specific optimizations, it is possible to get
~100-110MB/s for memcpy and ~270MB/s for memset on Nokia 770. 

More details and a link to the necessary code can be found here:
https://maemo.org/bugzilla/show_bug.cgi?id=733 

Maybe it is time to try getting these optimized functions integrated into
glibc for use on Nokia 770? Surely they need to be tested a bit more 
first. But improving core system components (glibc, xserver, SDL, ..) may 
help to make Nokia 770 at least a bit faster and more competitive.

Any comments are surely welcome. I wonder if it would be possible to 
get a community improved firmware for Nokia 770 created (with bootmenu
included, improvements to the kernel, gstreamer ogg vorbis support out of  
the box, some performance optimizations and bugfixes) and become
available for download somewhere? Because of proprietary parts, probably
this firmware should be hosted by Nokia in the standard place where the 
user needs to enter serial number to download it? Of course it would be
unofficial and unsupported just like the hacker's edition.