
6-8
Debug Interface
Rev. A
Copyright 2000 by LSI Logic Corporation. All rights reserved.
Note:
Watchpoints are similar to data aborts, the difference being
that when a data abort occurs, although the instruction
completes, the ARM7TDMI-S core prevents all subsequent
changes to the ARM7TDMI-S state. This action allows the
abort handler to cure the cause of the abort, and the
instruction to be re executed.
If a watchpoint occurs when an exception is pending, the core enters
debug state in the same mode as the exception.
6.3.3 Entry into Debug State on Debug Request
The ARM7TDMI-S core can be forced into debug state on debug request
in either of the following ways:
through EmbeddedICE programming (see
Section B.12,
“Programming Breakpoints,”
and
Section B.13, “Programming
Watchpoints”
)
by asserting the DBGRQ pin
When the DBGRQ pin has been asserted, the core normally enters
debug state at the end of the current instruction. However, when the
current instruction is a busy-waiting access to a coprocessor, the
instruction terminates and the ARM7TDMI-S core enters debug state
immediately (this action is similar to the action of nIRQ and nFIQ).
6.3.4 Action of the ARM7TDMI-S Core in Debug State
When the ARM7TDMI-S core enters debug state, the core forces
TRANS[1:0] to indicate internal cycles. This action allows the rest of the
memory system to ignore the ARM7TDMI-S core and function as normal.
Because the rest of the system continues to operate, the ARM7TDMI-S
core is forced to ignore aborts and interrupts.
Caution:
Do not reset the core while debugging, otherwise the
debugger will lose track of the core.
The system must not change the CFGBIGEND signal during debug. If
CFGBIGEND changes, the programmer’s view of the ARM7TDMI-S core
changes with the debugger unaware that the core has reset. Also make
sure that nRESET is held stable during debug. When the system applies
reset to the ARM7TDMI-S core (that is, nRESET is driven LOW), the