56F8355 datasheet(74/172 Pages) FREESCALE

74 / 172 page

56F8355 Technical Data, Rev. 17

Freescale Semiconductor

Preliminary

5.3.3

Fast Interrupt Handling

Fast interrupts are described in the DSP56800E Reference Manual. The interrupt controller recognizes fast

interrupts before the core does.

A fast interrupt is defined (to the ITCN) by:

1. Setting the priority of the interrupt as level 2, with the appropriate field in the IPR registers

2. Setting the FIMn register to the appropriate vector number

3. Setting the FIVALn and FIVAHn registers with the address of the code for the fast interrupt

When an interrupt occurs, its vector number is compared with the FIM0 and FIM1 register values. If a

match occurs, and it is a level 2 interrupt, the ITCN handles it as a fast interrupt. The ITCN takes the vector

address from the appropriate FIVALn and FIVAHn registers, instead of generating an address that is an

offset from the VBA.

The core then fetches the instruction from the indicated vector adddress and if it is not a JSR, the core starts

its fast interrupt handling.

Priority 0

Priorities 1, 2, 3

Priority 1

Priorities 2, 3

Priorities 2 or 3

Priority 3

1. See IPIC field definition in Part 5.6.30.2

Table 5-2 Interrupt Priority Encoding

IPIC_LEVEL[1:0]1

Current Interrupt

Priority Level

Required Nested

Exception Priority

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