Art Celestini wrote: > Today, true, self-modifying channel programs would require the use of a Start > I/O driver since it is the real (not virtual) channel program that actually > executes. The closest thing I've seen to that in MVS are specialized drivers > that use PCIs to monitor the progress of a channel program and then maybe > make > an on-the-fly change to a CCW depending on some status or item of input data. > > Such programs always have to allow for the possibility that the CCW to be > modified may have already been pre-fetched from storage by the IOP (thus the > change may not be in time). Typically the change is simple, like changing a > NOP to a TIC, and if the change doesn't get made in time, the NOP just ends > the channel program.
i remember something about VTAM specifying virtual=real under MVS .... so vtam application channel programs were directly executed. vtam would allocate additional buffers and update/modify channel program in a PCI interrupt appendage. under vm there is diagnose x'98' ... real i/o that allows similar capability, for virtual machine to do lock, unlock and real ccw execution. description here: http://publibz.boulder.ibm.com/epubs/pdf/hcse5b11.pdf from above: The subfunctions of DIAGNOSE code X'98' are LOCK, UNLOCK, and SSCH-Real. The requested subfunction is identified by a code in the Rx register. The LOCK subfunction locks a single 4 KB page of virtual machine storage in host real storage. In addition, it returns to the virtual machine the absolute storage address of the frame used to lock the guest page. The UNLOCK subfunction unlocks a single 4 KB page of virtual machine storage that was previously locked by DIAGNOSE code X'98'. ... snip ... recent posts self-modifying channel program http://www.garlic.com/~lynn/2007e.html#14 Cycles per ASM instruction http://www.garlic.com/~lynn/2007e.html#19 Cycles per ASM instruction http://www.garlic.com/~lynn/2007e.html#27 IBM S/360 series operating systems history ---------------------------------------------------------------------- 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
