[snip] > >What does the bt848 do with non-aligned addresses? Ignore the two low bits? > As far as I remember, yes. >> 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 My original windows driver did just that - a list of rectangles from DirectDraw clipper was turned into a RISC program. I'm not sure if that piece of code made it into the sample driver available in the Win98 DDK ( probably not ). 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. I don't know much about the other chips, but the main strength of the Bt848 is its support for the scattered physical memory. In my windows driver neither target memory nor the RISC program memory have to be physically contiguous. Alex
