mc56f801 Freescale Semiconductor, Inc, mc56f801 Datasheet - Page 44

• Manufacturer Part Number: mc56f801
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

5.3.1
Once the INTC 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 Vector Base
Address (VBA) and the vector number to determine the vector address, generating an offset into the vector
table for each interrupt.
5.3.2
Interrupt exceptions may be nested to allow an IRQ of higher priority than the current exception to be
serviced. The following table defines the nesting requirements for each priority level.
5.3.3
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:
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.
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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
Normal Interrupt Handling
Interrupt Nesting
Fast Interrupt Handling
SR[9]
0
0
1
1
Table 5-1 Interrupt Mask Bit Definition
SR[8]
0
1
0
1
56F8014 Technical Data, Rev. 9
Exceptions Permitted
Priorities 0, 1, 2, 3
Priorities 1, 2, 3
Priorities 2, 3
Priority 3
Exceptions Masked
Priorities 0, 1, 2
Priorities 0, 1
Priority 0
None
Fast Interrupt
Freescale Semiconductor
Preliminary