Hello Rob, I see what you are saying, but one thing that was a bit confusing (after some research) was the doc here that says "ESR (type 4) SVC - is type-2". http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/IEA2V260/1.4.3.112?SHELF=IEA2BK61&DT=20050713173259
But, I also from that see that I was a bit wrong in what I said: SVC 109 can route to a type-3 or type-4 SVC routine. So I guess my question here is really this: If I want to write an SVC routine and install it as an ESR SVC (SVC 109) and call it that way, then what type should my user-written SVC be? Type-3 or Type-4, or does it matter? The doc above says specifically: ESR (type 4) SVC - is type 2 But I didn't quite understand that. Seems SVC 109 is a type-2 that only calls type-4 SVC's, but that doesn't quit jive for me (yet). That was my question. (-: Lindy -----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Robert Wright Sent: Thursday, December 21, 2006 10:34 PM To: [email protected] Subject: Re: Question about SVC 109 Lindy Mayfield wrote on 12/21/2006 15:13:04: > Can someone please tell me if I have gotten this right? (: > > SVC's are numbered from 0 to 255. > > From 0 to 199 are reserved for IBM use. > > SVC 109 is basically an SVC that can call an SVC from 0 to 255, and > again IBM has reserved 0 - 199 for their own use. This in essence > extends the range of SVC's from 256 to 256*2. > > SVC's called by SVS 109 can only be type-4 SVC's. > > Why not type-3? Nowdays, I cannot see any differences between > type-3 and type-4. Am I missing something? SVC 109 is a distinct type-4 SVC in its own right, and it is a middle-man. By the early 1970s when it was created, IBM was running out of the 128 SVC numbers that we'd claimed for our own. SVC 109 was part of the answer. It steals one of the GPRs that other type-4 SVCs might want to use as part of their API and uses its contents as a function code. The function code determines which module, in turn, receives control from the middle-man. The functional module(s) deliver the function(s). SVC 109 has none of its own. Bob Wright - MVS Service Aids archives at http://bama.ua.edu/archives/ibm-main.html ---------------------------------------------------------------------- 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
