Nios II Classic Processor Reference Guide

ID 683620
Date 10/28/2016
Document Table of Contents External Interrupt Controller Interface

The EIC interface enables you to speed up interrupt handling in a complex system by adding a custom interrupt controller.

The EIC interface is an Avalon® -ST sink with the following input signals:

  • eic_port_valid
  • eic_port_data

Signals are rising-edge triggered, and synchronized with the Nios II clock input.

The EIC interface presents the following signals to the Nios® II processor through the eic_port_data signal:

  • Requested handler address (RHA)—The 32-bit address of the interrupt handler associated with the requested interrupt.
  • Requested register set (RRS)—The six-bit number of the register set associated with the requested interrupt.
  • Requested interrupt level (RIL)—The six-bit interrupt level. If RIL is 0, no interrupt is requested.
  • Requested nonmaskable interrupt (RNMI) flag—A one-bit flag indicating whether the interrupt is to be treated as nonmaskable.
    Table 73.  eic_port_data Signal
    Bit Fields
    44 ...
    ... 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Following Avalon® -ST protocol requirements, the EIC interface samples eic_port_data only when eic_port_valid is asserted (high). When eic_port_valid is not asserted, the processor latches the previous values of RHA, RRS, RIL and RNMI. To present new values on eic_port_data, the EIC must transmit a new packet, asserting eic_port_valid. An EIC can transmit a new packet once per clock cycle.

For an example of an EIC implementation, refer to the Vectored Interrupt Controller chapter in the Embedded Peripherals IP User Guide.