TIDAW requirements for EXCP requests

The input and output data pointers in the TCW may point to a single, contiguous area of storage, or may point to a virtual TIDAL that consists of one or more virtual TIDAWs, each of which may points to a contiguous area of storage. Unlike the zHPF channel programs created by EXCPVR, these storage areas may be larger than 4K and may span page boundaries.

During channel program translation EXCP creates a real TIDAL when any of the following is true:

The TCW input or output data pointer points to a virtual storage area that spans pages. For example, the TCW input address points to a 16K byte virtual storage area or points to a 2K byte area that crosses a page boundary.
The TCW points to a virtual TIDAL. Unlike CCW channel programs, the TIDAL may consist of multiple TIDAWs, each of which can point to a virtual storage area that spans pages. Supporting multiple TIDAWs is necessary for zHPF because there is only a single input and output area pointer (rather than one per CCW), so the storage areas are more likely to be scattered throughout virtual storage.