SIO Appendage

If you are using EXCPVR to execute a channel program and your channel program does not already contain real addresses, translate the virtual addresses in the operands of your channel program to central storage addresses. This should be done in the SIO appendage. If indirect data addressing is required, use the SIO appendage to build the indirect address lists (IDALs, MIDALs, or TIDALs) and turn on the appropriate indirect address list flag for the channel program.

You can use EXCPVR for VIO data sets with the following considerations for the SIO appendage:

The use of IDAWs and an IDAL is not required.
MIDALs and zHPF channel programs are not supported for VIO.
Addresses in the CSWs and IDAWs must be virtual. They must not be converted to central storage addresses.

The UCBVRDEB bit in the UCBJBNR byte can be checked to determine if the data set is being processed with VIO.

When building an IDAL for CCW channel programs consider the following:

Bit IOBEEIDA, described in Input/Output Block Common Extension (IOBE) Fields, specifies whether you are using 31-bit or 64-bit IDAWs. With 31-bit IDAWs, use 2 KB boundaries when determining whether a storage boundary is crossed for a CCW. With 64-bit IDAWs, use 4 KB boundaries.
The LRA instruction returns a 31-bit central storage address regardless of whether you are in 24-bit or 31-bit addressing mode, but fails in those addressing modes if the central storage address is above 2 GB. If the central storage address is above 2 GB, you must either use the LRAG or STRAG instruction to convert the virtual address to a real address or use the LRA instruction (after first switching to 64-bit addressing mode). If your program switches to 64-bit addressing mode, you must ensure that you save and restore the high 32 bits of any register that you modify. If you fail to do this, unpredictable results can occur for other 64-bit programs in your address space.

See IDAW Requirements for EXCP Requests for more information on creating IDAWs for EXCPVR requests.