The following message is a courtesy copy of an article that has been posted to bit.listserv.ibm-main as well.
[EMAIL PROTECTED] (Robert A. Rosenberg) writes: > There was also the secondary use of the high bit to signal AM24 vs > AM31 in addresses used for branching to/from subroutines. This > required replacing BALR with BASR and BR with BSM to do the AM Mode > Switch. 360/370 24bit psw had ILC/CC and program mask in adjacent byte; BAL/BALR not only saved the 24bit instruction address but also the next byte of the PSW (cc, and program mask). on return, not only could the calling/return address be restored, but SPM instruction would also be used to restore the program mask ... aka from principle of ops SPM programming notes: http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/dz9zr003/7.5.113?DT=20040504121320 1. Bits 34-39 of the general register may have been loaded from the PSW by execution of BRANCH AND LINK in the 24-bit addressing mode or by execution of INSERT PROGRAM MASK in either the 24-bit or 31-bit addressing mode. 2. SET PROGRAM MASK permits setting of the condition code and the mask bits in either the problem state or the supervisor state. 3. The program should take into consideration that the setting of the program mask can have a significant effect on subsequent execution of the program. Not only do the four mask bits control whether the corresponding interruptions occur, but the exponent-underflow and significance masks also determine the result which is obtained. ... snip .. BAS/BASR were introduced on 360/67 as part of supporting 32bit virtual addressing mode. retrenching to 370 ... not only was 360/67 32bit virtual addressing dropped ... but also the channel controller for multiprocessor support ... standard 360/67 multiprocessor not only allowed all processors to address all real storage but also all channels. standard 360 (and later 370) multiprocessor support only allowed two processors to address all of the (same) real storage ... but each processor was limited to only addressing their own, dedicated channels. some of the 360/67 control registers were also used to "sense" the switches on the channel controller (which governed the multiprocessor configuration settings ... not only for channels but also for real storage) ... these control register definitions were later taken over for "access registers" -- 40+yrs virtualization experience (since Jan68), online at home since Mar70 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
