[cairo] [Pixman] FPU requirement in SoC based devices

Koen Kooi k.kooi at student.utwente.nl
Wed Sep 1 11:15:23 PDT 2010

Hash: SHA1

On 26-08-10 18:00, Siarhei Siamashka wrote:
> On Wednesday 25 August 2010 04:36:27 M.R. wrote:
>> Floating point hardware is a reasonable requirement on a dedicated
>> SoC device that models some application-domain process that deals
>> with physical measurements and is thus by its nature best representable
>> with real numbers. But if the cost of hardware is critical and press
>> run is high, floating point should never be made necessary just to
>> reduce the display-driving software development cost,
> I don't quite like the wording "reduction of development cost". It's just that
> hardware platforms without a (fast) FPU unit are adding more diversity.
> Software developers now either have to "run after two hares", or make a choice
> about what class of hardware is the primary target to focus on. The other types 
> of hardware will lose some performance as a result, unless somebody puts an 
> effort into solving this problem by maintaining alternative optimized code 
> paths or introducing some clever improvements which work best for everyone.
> SoC devices without FPU still can run floating point code perfectly fine. They
> are just slow because floating point calculations are performed via software 
> emulation library.
>> especially if the only purpose of the display is man/machine interface (i.e.,
>> the "control panel" display), not the visualization of some application-
>> -domain process.

For the SoCs I use it is a bit more complicated. For example the
omap-l138 has a beefy floatingpoint DSP attached that will do the number
cruching for the application and the arm926 will run the gui code.
Similar situation for DM368, the video hardware will to the 1080p h264
encode/decode, the arm926 will run the gui code.
I'm still hoping that someone finds a way to run the heavy part of
pixman on the DSP, but till then having a floating point only pixman
isn't going to speed up the gui on arm926 class hw.


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