On 02/04/14 15:05, Michael Mrozek wrote:
Am Wed, 2 Apr 2014 13:48:29 +0200 hat "Dr. H. Nikolaus Schaller" hns@goldelico.com geschrieben:
Okay, got some replies from Solomon Systech :)
Well, I didn't study the specs, so perhaps they have some magic functionality there to support rotation. But afaik, the only way to have tear-free rotation with that kind of chip is that the chip has a double framebuffer, so that the other can be written to while the other is read from.
From my calculations of the chip it does not have enough memory for a double buffer - even for a 720x1200 panel
Reply from Solomon:
"Your engineer is correct, even with TE pin, it requires double frame buffer in order to avoid the tearing.
Since SSL compression is a 50% compression, each 720p frame data is 720x1280x24x50% which is roughly 11Mbit and we will do exactly what your engineer mentioned, to separate the Frame X and X+1 into 2 separate locations as a double frame (D2858 has ~27Mbit), and write IN as landscape and read OUT as portrait to perform the rotation."
So it DOES tearing free rotation.
Ah, that's interesting. Sounds like it could work, then. One thing to confirm is that the SSL compression can be used only inside the chip. I.e. OMAP can send uncompressed data to the chip, and the chip will send uncompressed data to the panel. The diagram on the SSD2858 spec does hint that way, though.
I've just asked him whether SSL compression is lossless, will let you know.
It'd also be nice to get any pointers about the compression. I couldn't find anything with quick googling.
But I know from video editing that a FullHD stream can easily be compressed to half the size without visible artifacts, most of the time lossless (as it's very unlikely that every pixel has a different color).
Unlikely or not, it must be clear that any image, even one with each pixel of different color, will fit into half of the framebuffer.
Btw, did you check the SSD2848 chip? I don't know the diff to SSD2858, but http://www.solomon-systech.com/en/product/mobile-system/mipi-master-bridge-c... says it just has less TX pins, and I guess 4 would be just fine for Pyra.
Tomi