On invocation, general-purpose register 1 points to the CSI parameter list.

The first word in the parameter contains an address that points to a 4-byte reason area. On return from CSI, the reason area contains a module identification, reason code and return code. See the section on Output for further discussion of this parameter.

The second word contains the address of the selection criteria fields. The selection criteria data fields supply information to CSI on invocation, and contain information for a resume if there is more information to be returned than can fit in the user-provided work area.

The third word contains the address of a user work area in which entry information will be returned. The caller must place the size of the work area in the first word of the work area. Although this area has no fixed size, it must be between 1024 bytes and 1,048,575 bytes, inclusive. On an initial call, the CSI will return the minimum size necessary to contain one entry, its catalog and fields included, and return code 32 will be set if the minimum size required is not specified. On a resume call, the required length field (CSIREQLN) from the previous call should always be checked to ensure that the return area size is large enough for the next entry.