On Tue, 15 Jul 2008 19:52:34 -0300 Werner Almesberger <[EMAIL PROTECTED]> babbled:
> Carsten Haitzler wrote: > > hmmmm. interesting idea. this is only possible to do sanely with dma > > You could probably control this also by carefully scheduling instructions. > E.g., instead of > > compute A and B > write A to glamo > write B to glamo > do C > > you could > > compute A > write A to glamo > compute B > write B to glamo > do C > > or > > compute A and B > write A to glamo > do C > write B to glamo > > This would be hell to implement for all accesses, but if you have > certain structures of accesses, they could be done in small hand-tuned > functions. For bulk transfers, you need DMA. oh man..not just hell - but nigh imposible. in general you compute a whole buffer of pixels - often a whole window or screen worth - or at least an update region of several hundred pixels - at a minimum, if not several thousand, ten-thousand, THEN you upload it when is done. ouch. it's likley not going to fly though. > It's an interesting idea. Whether it works depends largely when the > Glamo samples the data: at the beginning or at the end of the cycle. > > Whether it's useful also depends on whether there is really a lot of > other things the system can do. Since this is likely to be slower than > a burst copy, you only win if the bottleneck of the application isn't > the amount of data that gets moved to the Glamo. > > In a GUI, sheer transfer rate is probably the bottleneck. In video > playback, there may be an opportunity to interleave decompression > with frame buffer access. Should be fun to implement, though ;-) pretty much anything that does animation and is uploading data a lot - updated images, frames etc. is going to suffer badly from glamo. i've done tests with an old software-only 3d enigne i wrote years ago for 16bpp. if we have a 2442 with a dumb framebuffer i'd get 13fps. the glamo drops it to 7fps from 13 due to the wait on the copy-to-glamo, so that gives you an idea of the impact on a software 3d engine which does have enough computer to do between pixel uploads. the less compute needed for the pixel creation, the higher the impact. :( -- Carsten Haitzler (The Rasterman) <[EMAIL PROTECTED]>
