Why qtopia uses framebuffer and ASU can't?

Carsten Haitzler (The Rasterman) raster at rasterman.com
Mon Sep 8 01:30:09 CEST 2008

On Sun, 7 Sep 2008 21:34:52 +0000 "Leonti Bielski" <prishelec at gmail.com>

> Hello!
> Somewhere I read that Qtopia is much faster than other distros because
> it uses framebuffer. So I have some questions:

misnoma. wrong.

> 1. How is it possible for qtopia to bypass glamo chip and write
> directly to the framebuffer?

fb is available - but you will be competing with x for the fb and so you can
choose - either qtopia and all - or x. not both. you can use x to write to the
fb - it is simply an organised way of doing so. (ie you write to an shm buffer
then xshmputimage the regions u want).

> 2. Is it possible to do the same with x11 server?
> 3. Is there other explanation(except for glamo) why apps are slow to
> respond on 400mhz proc?

"bandwidth" to glamo - it holds the cpu in waitstates while writing to video
ram (the framebuffer) so all time spent writing is lost as cycles to do
anything else. and it's pretty slow (7mb/sec).

for example. lets say i spend 1 second to write data to video ram - that is 1
second i CANNOT spend on anything else. the glamo limits write rates to about
7mb/sec (so the memcpy() to video ram is artificially slowed down compared to
what it would be mem -> mem which would be about 50mb/sec so you lose about 85%
of your cpu cycles entirely while writing to video ram).

the glamo has acceleration - not everything, but a reasonable set (not really
any less than most desktop x drivers when it comes to 2d).

> Thank you!
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The Rasterman (Carsten Haitzler)    raster at rasterman.com

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