ARM7DMT contains hardware extensions for advanced debugging
features. These are intended to ease the user’s development of application
software, operating systems, and the hardware itself.
The debug extensions allow the core to be stopped either on
a given instruction fetch (breakpoint) or data access (watchpoint),
or asynchronously by a debug-request. When this happens, ARM7DMT
is said to be in debug state. At this point, the core’s internal state
and the system’s external state may be examined. Once examination
is complete, the core and system state may be restored and program
execution resumed.
ARM7DMT is forced into debug state either by a request on
one of the external debug interface signals, or by an internal functional
unit known as EmbeddedICE. Once in debug state, the core isolates
itself from the memory system. The core can then be examined while
all other system activity continues as normal.
ARM7DMT’s internal state is examined via a JTAG-style serial
interface, which allows instructions to be serially inserted into
the core’s pipeline without using the external data bus so, when
in debug state, a store-multiple (STM) could be inserted into the instruction
pipeline and this would dump the contents of ARM7DMT’s registers.
This data can be serially shifted out without affecting the rest
of the system.
PDF version