On Wed, 6 Sep 2000, Ralph Metzler < wrote: > The commands also only process one 32Bit DWORD of data at a time. > Windows should start on DWORD boundaries. If single bytes are to be How do you know this to be the case? While I would expect a dword alignment restriction on addresses and lengths for the sequencer commands, I can find no mention of such restrictions in the RISC section of the bt848 manual. What does the bt848 do with non-aligned addresses? Ignore the two low bits? > The bitmap now has to be translated to such RISC commands. I see that the current bttv driver turns the clipping rectangles into a bitmap, then turns the bitmap into a RISC program. It would be more efficient to go directly from a list of rectangles to a RISC program, and skip the bitmap step. When you want to change overlay on a frame by frame basis, this inefficiency really does make a difference. > Other PCI bridges like the Philips SAA7146 and, AFAIR, some ZORAN chips > provide bitmap clipping directly in hardware. I'd like to note that the bitmap method, e.g. the ZR36067 chip, is in general less efficient and less powerful than the BT848 method. It's only in the (rather obscure, IMHO) case of trying to use a stipple pattern as a overlay mask that the bitmap method is superior.
