bherr...@txfb-ins.com (Herring, Bobby) writes: > TOD Clock switch AFAIK came in with the 370. I remember it > specifically on the 168 my memory is iffy on the 155/158 but I think > it was there, no experience on the 14X . > > If it was there on the 360s I never heard/saw anything about it.
TOD was introduced with 370 (interval timer & clock comparator) ... relaxing location 80 timer. i remember getting caught up for a couple months discussing things like whether the TOD baseline of first day of the century was 1900 or 1901. lower-end 360s would update location 80 appox. every 3mills ... higher end 360 could have (high resolution) location 80 update approx every 13mics ... including 360/67. cp/67 used location 80 for everything ... it would save old value and load new value into 84, doing overloaping 8byte move from "80" to "76" (moved old value from 80 into 76 and new value from 84 into 80). It would then update the various clocks and timer values by the difference in current value saved to 76 and the original value that had been originally loaded into 80 (aka virtual machine microseconds used, kernel supervisor microseconds used, current clock value). when cp/67 was originally installed at the univ. in jan68 ... it had support for 1050 & 2741 terminals ... along with "automatic terminal identification". The univ. had some number of ascii/tty terminals ... so I had to add TTY terminal support. I extended the original logic for automatic terminal identification to include TTY. It worked fine for leased lines ... but had a glitch trying to do a single dailin phone number with "hunt group" (pool of lines). It was possible to change line-scanner associated with each port (terminal type) ... but that didn't actually change the line-speed for each port (1050 & 2741 were the same ... but ascii/tty was different). This somewhat prompted the univ. to do a clone controller effort ... reverse engineer channel interface and building channel interface board for Interdata/3 ... and programming Interdata/3 so it could do both line-speed and terminal type. This got four of us written up as responsible for (some part of) clone controller business ... since vendor picked up the implementation and sold it commercially. One of the first bugs testing on channel interface was 360/67 "red-light". The timer-tic hardware attempts to update location 80 on every tic ... if the processor or channel is holding the memory bus interface, it will delay ... but if delays so long that the timer tics again ... it will stop the processor with hardware failure. Turns out the initial clone controller implementation wasn't making sure that it told the channel interface to release the memory bus at least once every 13microseconds. The location 80 timer updates put expensive load on memory bus ... one of the reasons for starting to eliminate its use ... starting with tod, interval timer, and clock comparator in 370. -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
