Graphics Performance

Carsten Haitzler (The Rasterman) raster at
Fri Apr 3 02:02:28 CEST 2009

On Thu, 2 Apr 2009 18:23:38 +0200 Tobias Diedrich <ranma+openmoko at>

> Iain B. FIndleton wrote:
> > A significant issue for me is the performance of the graphics display on 
> > the FR. I recall some discussions a while back about making use of the 
> > XGlamo acceleration features. Has any progress been made here? It 
> > appears to me that the graphics performance on the FR is poor compared 
> > to, for instance, the iPhone or iTouch, both of which have slower CPUs. 
> > When applications running on the FR have their X output routed to a 
> > machine with accelerated graphics, it is apparent that the FR processor 
> > can deliver the X events fast enough, but the FR graphics chip interface 
> > can't keep up.
> Isn't the glamo supposed to have one (or more?) OpenRISC cores?
> It would be nice to have a documented way to upload code to the
> core, that way it might be possible to implement the Bling on the
> graphics chip directly...
> I mean, since OpenRISC has a documented instruction set (unless
> they've augmented it) set I'd figure the only thing missing would
>  be where to put the code and how to start it...

this information is not even in the docs openmoko had on the glamo. there is no
known way to play with this core. my understanding is that it is actually a
relatively slow core (50mhz) and is only really for higher level management of
sub-systems on the glamo.

of course here is your big problem.. you can do all this for the glamo and it
will never work anywhere else. it is a 1 off for 1 chip that will never see the
light of day in another product.

> So, just like with the mpeg4 decoding unit, wouldn't it be
> possible for someone with access to the NDA documentation to write
> an example program that just shows how to run a simple program (e.g.
> bitblt) on the OpenRISC processor?

no. as those docs are not even in the nda docs. other than that.. bitblit is
documented and not related to the risc core. there is a blitter there. xglamo
uses even. xglamo *IS ACCELERATED* it's about as accelerated as most x drivers
(fills, blits). it has no accel for xrender (xglamo doesnt implement enough of
xrender's operations to make it worth it - again see my previous mail. you'll
be writing fallback software code and end up no faster than where you started).

if you want decent speed - drop to qvga. thats what glamo was really designed
to handle. even the 2442 (cpu) is pushing it to deal with vga nicely. it can.
but that generation of cpu is more geared to qvga resolutions.

the gta02 is a ferrari body (vga screen) with a lawnmower engine under it (2442
+glamo). you need to drive it like a lawnmower - and then only expect it to be
as good as a lownmower. it looks nice parked on the street (still photos) but
if it moves... it will show its true nature. remove the heavy ferrari body and
drive it like a go-kart and you'll have more fun.

> -- 
> Tobias						PGP:
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