Extended TOD-clock facility

The extended TOD-clock facility provides an extended form TOD clock and a TOD programmable register. The extended form TOD clock is a 128- bit value that extends the current basic form by appending 8 bits on the left and 56 bits on the right. The extended form TOD clock is returned by a problem-program instruction, STORE CLOCK EXTENDED (STCKE). The contents of the TOD programmable register are stored into the rightmost portion of the extended form TOD value when the TOD clock is inspected by STCKE. A TOD programmable register exists for each CPU and contains the TOD programmable field in bits 16-31. The TOD programmable register is set by a new privileged instruction, SET TOD PROGRAMMABLE FIELD (SCKPF). The leftmost byte of the extended form TOD clock is the TOD Epoch Index (TEX), and is stored as zeros in machines running General.

The extended TOD clock facility satisfies three main objectives:

• Relieve constraints that exist in the current 64- bit TOD clock
• Extend the TOD-clock architecture to multi-system configurations
• Help ensure sysplex-wide uniqueness of the STCKE TOD values

The TOD Programmable Field (TODPF) is a 16- bit quantity contained in bit positions 16-31 of the TOD programmable register. The contents of the register can be set by the privileged instruction SET TOD PROGRAMMABLE FIELD. The contents of the register can be stored by the instruction STORE CLOCK EXTENDED, which stores the TOD programmable field in the last 16 bits of the extended form TOD clock. The contents of the register are reset to a value of all zeros by an initial CPU reset.