Like Event Handling for application software, an Interrupt is an electronic way of letting devices call the CPU on a hardware event.

Used by

      keyboard
      mouse
      network card
      modem

Other interrupts

      timer
      power

In robots, there may be many interrupts, and interrupt are many hardware devices and interrupt handling will be an important part of the architecture.

special purpose distributions server desktop embedded system

Interrupt ReQuest (IRQ) What is interrupted? The CPU.

cat /proc/interrupts one row for each IRQ one column for each CPU, showing the count of interrupts of that IRQ

Programmable Interrupt Controller (PIC) Advanced PIC (APIC) A PIC is connected to the CPU, via a port and the INTR pin. Devices are connected to the PIC, via an IRQn pin. Flow: * A device raises an interrupt (voltage) on the PIC’s IRQn pin. * The PIC converts the IRQ to a number and writes it to a port, and then raises an interrupt on the CPU’s INTR pin. * The CPU reads the number from the port. * The CPU handles the interrupt. * The CPU signals back an acknowledgement to the PIC, who has been waiting for this completion.

top half: the hard IRQ bottom half: the soft IRQ

hard IRQ vs polling mainline kernel vs runtime (RT) kernel

interrupt is the device’s way to notify the cpu that it needs attention hard vs soft level vs edge-triggered, simple, fast EOI local vs global system vs device maskable vs not shared vs not multiple

proc interrupts mpstat -A

which devices support IRQs?