st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 77

• Manufacturer Part Number: st20-gp6
• Description: Gps Processor
• Manufacturer: STMicroelectronics

ST20-GP6
14.3 Software debugging features
14.3.1 Control of the target CPU including boot
Various state information about the target CPU may be monitored and the CPU may be controlled
from the diagnostic controller via the TAP. The control of the CPU extends to stalling, forcing a trap
and booting.
14.3.2 Non-intrusive Iptr profiling
A copy of the Iptr is visible as a read-only register in the diagnostic controller. This register may be
read at any time. Reading this register is not intrusive on the CPU or its memory space.
14.3.3 Events
Support is provided by the diagnostic controller to trigger actions when certain predefined events
occur.
Breakpoint
The function of the breakpoint is to break before the instruction is executed, but only if it really was
going to be executed. A 32-bit comparator is used to compare the breakpoint register against the
instruction pointer of the next instruction to be executed. The matched instruction is not executed
and the CPU state, including all CPU registers, is defined as at the start of the instruction. The pre-
vious instruction is run to completion.
Breakpoint range
The function of a breakpoint range is equivalent to any single breakpoint but where the breakpoint
address can be anywhere within a range of addresses bounded by lower and upper register val-
ues.
Watchpoint
The function of a watchpoint is to trigger after a memory access is made to an address within the
range specified by a pair of 32-bit registers. The CPU pipeline architecture allows for the CPU to
continue execution of instructions without necessarily waiting for a write access to complete. So, by
the time a watchpoint violation has been detected, the CPU may have executed a number of
instructions after the instruction which caused the violation. If the subsequent action is to stall the
CPU or to take a hardware trap, then the last instruction executed before the stall or trap may not
be the instruction which caused the violation.
Datawatch
The function of a datawatch is to trigger after a data value specified in one 32-bit register is written
to a memory word address specified in another 32-bit register. The subsequent action is equivalent
to a watchpoint.
Scheduling events
Various scheduling events can be detected.
Choice of subsequent actions
Following a watchpoint match, or any other condition detectable by the diagnostic controller, the
subsequent action may be programmed to be one of the following:
•
stall the CPU, i.e. inhibit further instructions from being executed by the CPU;
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