Introduction
Part 5 Interrupt Controller (ITCN)
5.1 Introduction
The Interrupt Controller (ITCN) module is used to arbitrate between various interrupt requests (IRQs), to
signal to the 56800E core when an interrupt of sufficient priority exists, and to what address to jump in
order to service this interrupt.
5.2 Features
The ITCN module design includes these distinctive features:
•
•
•
•
Programmable priority levels for each IRQ
Two programmable Fast Interrupts
Notification to SIM module to restart clocks out of Wait and Stop modes
Drives initial address on the address bus after reset
For further information, see Table 4-5, Interrupt Vector Table Contents.
5.3 Functional Description
The Interrupt Controller is a slave on the IPBus. It contains registers allowing each of the 86 interrupt
sources to be set to one of four priority levels, excluding certain interrupts of fixed priority. Next, all of
the interrupt requests of a given level are priority encoded to determine the lowest numerical value of the
active interrupt requests for that level. Within a given priority level, zero is the highest priority, while
number 85 is the lowest.
5.3.1
Normal Interrupt Handling
Once the ITCN has determined that an interrupt is to be serviced and which interrupt has the highest
priority, an interrupt vector address is generated. Normal interrupt handling concatenates the VBA and the
vector number to determine the vector address. In this way, an offset is generated into the vector table for
each interrupt.
5.3.2
Interrupt Nesting
Interrupt exceptions may be nested to allow an IRQ of higher priority than the current exception to be
serviced. The following tables define the nesting requirements for each priority level.
Table 5-1 Interrupt Mask Bit Definition
SR[9]1
SR[8]1
Permitted Exceptions
Masked Exceptions
None
0
0
1
1
0
1
0
1
Priorities 0, 1, 2, 3
Priorities 1, 2, 3
Priorities 2, 3
Priority 3
Priority 0
Priorities 0, 1
Priorities 0, 1, 2
1. Core status register bits indicating current interrupt mask within the core.
56F8366 Technical Data, Rev. 6
Freescale Semiconductor
Preliminary
83
FREESCALE [ Freescale ]
