Handling system interrupts

An interrupt is a hardware-enforced transfer of control. There are five types of interrupts: external, input/output (I/O), machine check, program check, and supervisor call (SVC). Table 1 summarizes the different types of interrupts, which areas of the control program process them, and what causes them.

Table 1. System interrupts
Type of Interrupt Processed By Caused By
External External interrupt handler (CTME)
  • Signal from the interrupt key on the system console
  • TOD clock comparator
  • CPU timer
  • Sysplex Timer
  • Server Time Protocol (STP)
  • TOD clock sync checks
  • Service signals
  • Malfunction alerts
  • External calls.
I/O Common I/O handler (CCIO) Status from an I/O operation
Machine check Machine check handler (CMKH)
  • Equipment malfunction (hardware error)
  • Server Time Protocol (STP)
Program check System error processor (CPSE) Programming error
SVC SVC macro decoder (CEDM) Supervisor call instruction