Shared TOD clock modification bit

摘要: A shared time-of-day (TOD) clock modification bit is used in a multiprocessing system which the timing facilities two or more CPUs are implemented as function of single TOD clock. This helps avoid timer errors that occur result one central processing unit (CPU) changing value while another CPU executing an instruction determines value. Whenever microcode any reads clock, it obtains Shared Clock Modification Bit addition to indicates if read operation just completed first such executed by since was updated sharing same If is, certain instructions take action correct introduced change