Digi Rabbit 5000, User Manual

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334 Rabbit 5000 Microprocessor User’s Manual
28.2 Dependencies
28.2.1 I/O Pins
There are no I/O pins associated with breakpoints.
28.2.2 Clocks
There are no clocks associated with breakpoints.
28.2.3 Other Registers
There are no other registers associated with breakpoints.
28.2.4 Interrupts
When an enabled address match occurs for a given breakpoint, a breakpoint interrupt
occurs. The breakpoint that caused the interrupt must be determined by reading BDCR,
which also clears the interrupt. Any of the breakpoint interrupts can be enabled by writing
to BDCR.
The breakpoint interrupt vector is in the EIR at offset 0x040. It is always set to Interrupt
Priority 3, and is the highest priority interrupt; if two Interrupt Priority 3 vectors are pend-
ing, the breakpoint interrupt will always be handled first.
28.3 Operation
The following steps must be taken to enable breakpoints:
1. Write the vector to the interrupt service routine to the external interrupt table.
2. Write the desired breakpoint addresses to the appropriate breakpoint address registers
(BxAyR, where x is the breakpoint and y is the byte of the address, 0-2).
3. Write an address mask for the given breakpoints (BxMyR).
4. Select the breakpoint address match type (execute, data read, data write) by writing to
the appropriate BxCR.
5. Enable the desired breakpoints by writing to BDCR.
28.3.1 Handling Interrupts
The following actions occur within the interrupt service routine.
•
Which breakpoints are pending should be determined by reading BDCR. This also
clears the pending breakpoints.
•
The desired breakpoint action should be taken.
•
If single-step functionality is desired, the breakpoint interrupt should be re-enabled by
writing the appropriate bit to BDCR. If this is done, the interrupt handler needs to be
exited in a particular manner (see below).