ST20-GP6 datasheet(77/123 Pages) STMICROELECTRONICS

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ST20-GP6

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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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