EXCP macro users can perform I/O to virtual storage areas above
16 megabytes. With the virtual IDAW support, CCWs in the EXCP channel
program can use a 24-bit address to point to a virtual IDAW that contains
the 31-bit virtual address of an I/O buffer. The CCWs and IDAWs themselves
must reside in virtual storage below 16 megabytes. The EXCP service
routine supports format 0 and format 1 CCWs.
Any CCW that causes data to be transferred can point to a virtual IDAW. Virtual IDAW support is limited to non-VIO data sets.
Although the I/O buffer can be in virtual storage above 16 megabytes, the virtual IDAW that contains the pointer to the I/O buffer and all the other areas related to the I/O operation (CCWs, IOBs, DEBs, and appendages) must reside in virtual storage below 16 megabytes.
Note: EXCP can translate your virtual channel program to
a real channel program that uses 64-bit IDAWs if you are running in z/Architecture mode
and the device support code allows them.
For more EXCP information, see z/OS DFSMSdfp Advanced Services.