If the device that you wish to emulate has a certain feature that (1) you wish to support, (2) IBM software and hardware supports such a feature, but (3) you cannot use that feature if you write your I/O requests using EXCP, then you will need to use STARTIO somewhere in your emulation. You will probably not need to use it for all your I/O requests, but you will for all those particular I/O requests that cannot be done using any other IBM software.
You could always use a supported way if there is a supported way. If you don't need to use STARTIO, you should probably not use it. Only you will know if you need to use STARTIO or not in any given situation. Then there is always this solution: write a virtual machine that runs under VM/CP and which supports your hypothetical device. Then you can use the SSCH instruction if you wish, and do any bizarre thing that the PoO book says is possible but which neither EXCP, STARTIO, nor z/OS supports (e.g., address-limit checking[1]). Bill Fairchild Rocket Software [1] not supported by z/OS as far as I know. One way to find out what z/OS supports is to look at the DSECT for the IOSB (IECDIOSB), look at the ORB DSECT (IHAORB), and see if there are any flag bits in the ORB for which there is not a corresponding flag bit in the IOSB which would cause the ORB's corresponding flag bit to be turned on when the ORB is built based on the information in the IOSB. But make sure that the ORB DSECT you are using also has all the flag bit definitions in the latest version of the PoO before you start. -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@bama.ua.edu] On Behalf Of Lindy Mayfield Sent: Tuesday, June 21, 2011 12:20 PM To: IBM-MAIN@bama.ua.edu Subject: Re: Some tests with MFNetDisk PRO I totally apologize if I am beating the dead horse. But if I understood correctly, software that emulates a device like MFNet could be done with a supported means/interface, and I assume from what I read would be EXCP running authorized. So if I wanted to write something like MFNet (and i don't) would I have to use STARTIO? Or could I used a supported way. And if I don't need to use STARTIO, then when would I choose it? Regards! Lindy ________________________________________ From: IBM Mainframe Discussion List [IBM-MAIN@bama.ua.edu] On Behalf Of Bill Fairchild [bi...@mainstar.com] Sent: 21 June 2011 19:47 To: IBM-MAIN@bama.ua.edu Subject: Re: Some tests with MFNetDisk PRO I tried to do something like that around 1985. At the time I was using EXCP in an authorized program to do most of the same things that STARTIO will allow you to do but unauthorized EXCP will not, such as do I/O to an offline device, do I/O to an unallocated DASD track, etc. ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- 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
