On Monday, 11/03/2008 at 12:50 EST, "Schuh, Richard" <[EMAIL PROTECTED]> wrote:
> I hope one would never do a SSCH (or SIO back in the days) without > immediately checking for CC \= 0. If one is programming at that level, > it is likely that they are also handling the I/O interrupts, obviating > the need for following S*** with T***. I don't remember ever following > SIO with TIO or SSCH with TSCH without some intervening condition that > required it, and I have written channel programs that ran under several > platforms (OS/MFT, OS/MVT, SVS, CMS (4 different releases), TPF (3 > different releases) and a special purpose O/S that was IPLed in a > virtual machine. It is possible that my memory is failing me, but that > is how I remember it. A TSCH loop is used when you are disabled for interrupts (and don't feel like enabling) in response to CC=0 from SSCH. CP is smart enought to detect a TSCH loop and place the virtual machine in a semi-enabled wait. If you are enabled for I/O interrupts you issue a single TSCH or STSCH *in the FLIH* to read and clear the interrupt status. The SLIH will typically drive a callback of some sort. Alan Altmark z/VM Development IBM Endicott
