AWCTTYPA@UIAMVS.BITNET ("David A. Lyons") (11/20/88)
>Date: Fri, 18 Nov 88 03:36:46 GMT >From: Doug Gwyn <haven!adm!smoke!gwyn@AMES.ARC.NASA.GOV> >Subject: Re: Bad Clock/Crystal in GS >In article <8811162247.aa01906@SMOKE.BRL.MIL> JCKASPER@MTUS5.BITNET writes: >:for System Speed that says either FAST or NORMAL. Well... regardless >:of what my GS is set to it runs according to a SIN wave. A sin wave with >:an amplitude of 1/10 Mhz to 10 Mhz and a period (duration of cycle) of >:2-5 minutes. Needless to say... this is rather anoying. Does anybody >:have any suggestions as to what might be wrong? >Yes -- you need to find a better drug dealer. I haven't received JCKASPER's original note, but could this have something to do with the difference between reading from ROM and reading from RAM? As I recall, the clock speed is 2.8 MHz, but it's effectively slowed down by wait states (?) to 2.5 MHz if you're reading from (fast) RAM, since sometimes the RAM is already busy being refreshed when you want to read it. Anyway, if the sampling period being used to measure the frequency was relatively short, and the computer was doing something repetitive where it spent part of the time reading from ROM and part reading from RAM, I can see how "interference patterns" might be generated that would make it look like the frequency was varying in a repetitive pattern, with an amplitude of less than 3/10 MHz. Sort of like watching a picture of a TV picture _on_ a TV and getting slow interference from the not-quite-exactly-60Hz scan rates. I need more info to figure out why you're measuring about 2.5 MHz even when the control panel is set to Normal (1 MHz). Note that the control panel only determines the default value for a $C0xx location that actually controls the speed. So: o Software is free to override the speed setting; o The ROM in face _does_ override the speed setting and switch into high gear _temporarily_; but if you're measuring the hardware clock and spending all or almost all of the time _in_ some ROM routine (like the blinking-checkerboard get-a-key routine, the machine may be in Fast mode most or all of the time). o There is a small but nonzero chance when NOT running GS-specific event-driven software that when you hit Apple-Ctrl- ESC you will interrupt the system at a very unlucky spot: a ROM routine may have preserved the _old_ system speed on the stack so it can put the speed back where it was. If you change the speed, exit the control panel, and that ROM routine takes control back, finished what it was doing, and then sets the system speed back to the value it had when the routine was entered, your control panel setting seems to have had no effect. (In this case, your setting is still stored in the battery-RAM and will take effect if you reboot or hit RESET, for example.) Or, _possibly_, you need to get a better drug dealer. :-) --David A. Lyons bitnet: awcttypa@uiamvs DAL Systems CompuServe: 72177,3233 P.O. Box 287 GEnie mail: D.LYONS2 North Liberty, IA 52317 AppleLinkPE: Dave Lyons