STR910FAZ32H6T STMICROELECTRONICS [STMicroelectronics], STR910FAZ32H6T Datasheet - Page 29

• Manufacturer Part Number: STR910FAZ32H6T
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

STR91xFAx32 STR91xFAx42 STR91xFAx44
3.15.4
3.16
JTAG EmbeddedICE-RT protocol on the STR91xFA. These protocol converters are
commercially available and operate with debugging software tools.
The CPU may be forced into a Debug State by a breakpoint (code fetch), a watchpoint (data
access), or an external debug request over the JTAG channel, at which time the CPU core
and memory system are effectively stopped and isolated from the rest of the system. This is
known as Halt Mode and allows the internal state of the CPU core, memory, and peripherals
to be examined and manipulated. Typical debug functions are supported such as run, halt,
and single-step. The EmbeddedICE-RT logic supports two hardware compare units. Each
can be configured to be either a watchpoint or a breakpoint. Breakpoints can also be data-
dependent.
Debugging (with some limitations) may also occur through the JTAG interface while the CPU
is running full speed, known as Monitor Mode. In this case, a breakpoint or watchpoint will
not force a Debug State and halt the CPU, but instead will cause an exception which can be
tracked by the external host computer running monitor software. Data can be sent and
received over the JTAG channel without affecting normal instruction execution. Time critical
code, such as Interrupt Service Routines may be debugged real-time using Monitor Mode.
JTAG security bit
This is a non-volatile bit (Flash memory based), which when set will not allow the JTAG
debugger or JTAG programmer to read the Flash memory contents.
Using JTAG ISP, this bit is typically programmed during manufacture of the end product to
prevent unwanted future access to firmware intellectual property. The JTAG Security Bit can
be cleared only by a JTAG “Full Chip Erase” command, making the STR91xFA device blank
(except for programmed OTP bytes), and ready for programming again. The CPU can read
the status of the JTAG Security Bit, but it may not change the bit value.
Embedded trace module (ARM ETM9, v. r2p2)
The ETM9 interface provides greater visibility of instruction and data flow happening inside
the CPU core by streaming compressed data at a very high rate from the STR91xFA though
a small number of ETM9 pins to an external Trace Port Analyzer (TPA) device. The TPA is
connected to a host computer using USB, Ethernet, or other high-speed channel. Real-time
instruction flow and data activity can be recorded and later formatted and displayed on the
host computer running debugger software, and this software is typically integrated with the
debug software used for EmbeddedICE-RT functions such as single-step, breakpoints, etc.
Tracing may be triggered and filtered by many sources, such as instruction address
comparators, data watchpoints, context ID comparators, and counters. State sequencing of
up to three triggers is also provided. TPA hardware is commercially available and operates
with debugging software tools.
The ETM9 interface is nine pins total, four of which are data lines, and all pins can be used
for GPIO after tracing is no longer needed. The ETM9 interface is used in conjunction with
the JTAG interface for trace configuration. When tracing begins, the ETM9 engine
compresses the data by various means before broadcasting data at high speed to the TPA
over the four data lines. The most common ETM9 compression technique is to only output
address information when the CPU branches to a location that cannot be inferred from the
source code. This means the host computer must have a static image of the code being
executed for decompressing the ETM9 data. Because of this, self-modified code cannot be
traced.
Functional overview
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