In a message dated 11/21/2007 5:31:09 A.M. Central Standard Time, [EMAIL PROTECTED] writes:
:>The manual gives a further explanation: :>MVS does not guarantee preservation of the interrupt status of :>programs that explicitly disable for I/O and external interrupts :>through the STNSM instruction. :>What does 'does not guarantee' mean? I would presume that should the code be interrupted (PIC-10/11, restart, etc.) the masking bits in the old PSW may not be preserved and upon redispatch the PSW may be enabled for interrupts. Basically it means - under MVS, do not use STNSM - take the CPU lock. There must be more to it than that. The IBM module IOSVSSCQ (BALR-ed to in the expansion of the STARTIO macro) has a STNSM PSASYMSK as its 3rd instruction (preceded only by a BASR and AHI in the system I am using). I have studied the source code of this module extensively, and remember that later in this module the UCB lock for the device involved is obtained. What happens if an interrupt occurs between the STNM and the SETLOCK? I don't think that IOS would like it if its interrupt status was not preserved. The STARTIO macro can be issued by any authorized code whether it is enabled or disabled and whether it holds a lock or not. Another clue is that in the PSA DSECT the comment on the PSASYMSK byte says this: "This field will be used in conjunction with the STNSM instruction to place IOS channel scheduler into a disabled state ..." If you scan this whole DSECT for "STNSM" you will find several such fields that are used to hold the system mask upon doing a STNSM and even more STOSM instructions whose operands are the PSA bytes where various STNSMs saved the mask. Translation: IBM's use of the STNSM to disable interrupts explicitly within the nucleus is rife, so why do they externally document that it should not be done? Bill Fairchild Franklin, TN **************************************Check out AOL's list of 2007's hottest products. (http://money.aol.com/special/hot-products-2007?NCID=aoltop00030000000001) ---------------------------------------------------------------------- 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
