Trent Piepho writes: > 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? I think it behaved that way although it was not documented. This was 4 years though. I might be wrong. > > 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. I didn´t do it :-) The bitmap clipping was added after I stopped bttv development. > > 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. Of course it depends on what kind of clipping you want to do. The SAA7146 even supports window clipping (max. 16 windows) and bitmap clipping in hardware. Ralph
