hallett@hamlet.steinmetz (Jeff A. Hallett) (01/06/88)
Hey all you hardware jocks out there!! :^) Does anyone know how fast the 68881 can do a multiply-add? Jeffrey A. Hallett (ARPANET: hallett@ge-crd.arpa Software Technology Program UUCP: desdemona!hallett@steinmetz.uucp) General Electric Corporate Research and Development "The needs of the few outweigh the needs of the many" -- Kirk (STIII)
fiddler%concertina@Sun.COM (Steve Hix) (01/07/88)
In article <8368@steinmetz.steinmetz.UUCP>, (Jeff A. Hallett) writes: > > Does anyone know how fast the 68881 can do a multiply-add? Well, it depends... What clock rate is your 68881 running at? What is the format of the memory source or destination operand? What addressing mode are you using? (If I'm reading one of the tables in the "MC68881 Floating- Point Coprocessor User's Manual" rightly, the FMUL instruction can take anywhere from 71 to 908 cycles to execute. This don't allow for instruction/data fetch and write time... It might be easier to just find a Mac with the chip in it and write your own benchmark to exercise the '881 and find a typical time for the application sort of thing you're doing. (But we all know about bench- marks, don't we? :} ) Or you could get the Motorola '881 manual (MC68881UM/AD) and wallow around in Chapter 6 for a while. seh