Path: utzoo!utgpu!watmath!att!tut.cis.ohio-state.edu!ucbvax!vangogh.Berkeley.EDU!melvin From: melvin@vangogh.Berkeley.EDU (Steve Melvin) Newsgroups: comp.arch Subject: Re: Cycle Counter Summary: High resolution timers in Suns Message-ID: <30642@ucbvax.BERKELEY.EDU> Date: 15 Aug 89 08:52:35 GMT References: Sender: usenet@ucbvax.BERKELEY.EDU Reply-To: melvin@vangogh.Berkeley.EDU.UUCP (Steve Melvin) Distribution: comp Organization: University of California, Berkeley Lines: 47 In article grunwald@flute.cs.uiuc.edu writes: > >Hi, > >Another ``how much does this cost'' question. > >When doing performance monitoring, benchmarking or profiling, you want >a high-resolution timer. Some systems have microsecond timers, and >those are considered pretty snazzy; I know I was overjoyed when I >found one on the Encore. Normal machines, e.g., a Sun, have about 5 >millisecond resolution. That's pathetic. First, some clarification. All Sun 3's and Sun 4's lack a high resolution timer. Sun 2's had them and SPARCstations have them. In the Sun 3's and Sun 4's there is a 10ms hardware interrupt which in SunOS is ignored every other time to generate a 20ms interrupt for use by the operating system. Fortunately, however, Sun put sockets in these machines for data encryption chips (the whole encryption chip story is interesting in itself). Another grad student here at Berkeley (Peter Danzig) and I have designed a small board which plugs into these machines and allows a timer chip (being clocked at 4Mhz) to look like the encryption chip. Then, with an appropriate device driver installed, the software has access to high resolution time measurements just as though the feature was built in. Apparently, Sun at one time had intended to sell a data encryption option for these machines. The encryption chip provided for was the AMD Am9518 (which implements the official data encryption standard (DES)). In the 3/50 and 3/60, all that was needed was to plug the chip in (and move a jumper in the case of the 3/50) but in later models chips needed to drive the 9518 (one or two PALs and a buffer) were not supplied on the motherboard. The idea was apparently dropped and as far as we know the DES option has never been made available. It probably had a lot to do with the Feds (the DES chip is supposedly not allowed to be exported from the US). Having the socket enabled by a PAL may have had something to do with controlling the use of the DES chip. Anyway, I think the answer to your question is that these kinds of things cost very little in hardware and don't slow anything down, but since they don't tangibly affect the bottom line performance, they are often ignored by hardware designers. ------- Steve Melvin ...!ucbvax!melvin melvin@polaris.Berkeley.EDU -------