tas@unc.UUCP (Tim Seaver) (11/18/83)
I've heard that VMS has some tools for microcoding VAXen. Has anyone developed anything along those lines for UNIX or even investigated the possibility?
henry@utzoo.UUCP (Henry Spencer) (11/23/83)
I'm not sure about the 750 and below, but I saw a study several years
ago which implied that microprogramming the 780 was a dead loss. Seems
the user-microcode feature on the 780 is basically a marketing ploy, not
a useful piece of hardware. The dispatching overhead for user-defined
instructions (i.e., the time needed for the 780 to realize that it's
got a user-microcode instruction and call your microcode) is so large
that your user-defined instruction better be doing something really heavy
or else it will be a net speed *loss*.
I have also heard that it is nearly impossible to get documentation from
DEC describing how 780 microcode works, even if you buy a 780 with the
writeable-microcode box!
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry