It's not "counting at [n] cycles per [unit]" ; it's "counting at [frequency] in bit position [position]. That means that the scaling of the decrement depends on the frequency at which you decrement the interval timer.
Why should the descriptions of a software construct agree with the hardware used to support it. A TU represents the effective interval for changing bit 30, not bit 31. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@listserv.ua.edu> on behalf of Paul Gilmartin <0000000433f07816-dmarc-requ...@listserv.ua.edu> Sent: Monday, February 26, 2018 12:46 PM To: IBM-MAIN@listserv.ua.edu Subject: Re: Timer Unis (was: ... time change ...) On Mon, 26 Feb 2018 17:07:50 +0000, Seymour J Metz wrote: >Timer units are the same for the S/360 and the S/370. From GA22-7000-4 : >"In each case, the frequency is adjusted to give counting at 300 cycles per >second >in bit position 23. The cycle of the timer is approximately 15.5 hours. " > With some aritmetic: 503 $ rexx say 2**23 / 300 /60 / 60 7.76722963 So, this gives counting at one cycle per 7.77 hours in bit position 0. What does "counting at [n] cycles per [unit]" mean? How can this agree with the description of the TIMER macro? : For TUINTVL, the address is a fullword containing the time interval. The time interval is presented as an unsigned 32-bit binary number; the low-order bit has a value of one timer unit (approximately 26.04166 microseconds). Again, some arithmetic: 506 $ rexx say 1000000 / 300 / 2**( 31 - 23 ) 13.0208333 13.020833 µsec, not 26.04166. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
