Execute Channel Program in Real Storage: Difference between revisions

Revision as of 05:50, 24 August 2011

Revision as of 05:55, 24 August 2011

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{{Mainframe I/O access methods}}

In [[IBM mainframe]] [[operating system]]s, '''Execute Channel Program in Real Storage''' ('''EXCPVR''') is a supervisor call for low-level device access, where the programmer is responsible for providing a list of device-specific [[Channel_command_word#Channel_command_words|CCWs]], that is, a channel[[Channel_program#Channel_Program|Channel programProgram]], to be executed by I/O channels, control units and devices. Additionally, the programmer is expected and required to ensure that the input/output data areas are in real storage and are "fixed".

EXCPVR may be viewed, historically, as a V=R version of [[Execute Channel Program|EXCP]]. However, EXCPVR is not restricted to V=R applications. Indeed, EXCPVR may refer to non-V=R data areas provided such data areas are "fixed" and the channel command words which reference such data areas have been translated from virtual to real addresses by the programmer using the LRA privileged instruction. EXCPVR was first introduced in SVS and was continued in MVS/370. In the later instances of the OS, support was added for Format 1 CCWs, and, hence, for access to data areas which are "above the line". The user of EXCPVR must be authorized and must remain in supervisor mode and key throughout the EXCPVR process.