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Chapter 8 Debugging Functions
The R3900 Processor Core has the following support functions for debugging that have been added to the
R3000A instruction base. They are independent of the R3000A architecture, which makes them transparent to
user programs.
The real-time debugging system is supported by a third party.
Debug exceptions (Single Step, Break Instruction)
Additional register (DEPC) for holding the PC value when a debug exception occurs
Additional register (Debug) for controlling debug exceptions
Additional instruction (DERET) for return from a debug exception
8.1 System Control Processor (CP0) Registers
When a debug exception occurs, only registers Debug and DEPC are updated. The registers accessed by user
application programs (general-purpose registers, Status, Cause, EPC, BadVAddr, PRId, Config and Cache)
retain their values.
Figure 8-1 CP0 Registers
EPC register
BadVAddr register
Status register
Cache register
†
Config register
†
†
R3900 Processor Core additional
registers not present in R3000A
<Exception Processing>
PRld register
Cause register
Debug register
†
<Debugging>
DEPC register
†