Recently, I came to know about ETM(Embedded Trace Macrocell). This
is to trace instruction of program to know the bugs.
The same can be achieved by ITM(Instrumentation Trace Macrocell) by
using printf() statement.We can know the bugs by using ITM also. This
is not using any controller ports.
Then what is the importance of ETM? Can anyone tell? I couldn't
understand it. Debuggers with ETM are higher in cost. What's the
purpose of that?
ITM means you can create a debug channel for sending messages from
your code to the debugger.
ETM means that the chip hardware can stream out step-by-step how
it walks through the instruction stream. There is heavy data
compression involved so it basically just informs the debugger with
"y", "n", "n", "y" if it takes jumps or not.
This means the debugger on the PC can recreate a virtual copy of the
instruction sequence the processor performs.
So you can look back in time and evaluate the instruction sequence
that led the program into a specific state.
This is a big advantage if you need to solve issues with magically
hanging software, programs making unexpected jumps, getting stuck in
interrupt service routines etc.
So ETM is very good when your program performs unexpected
And ITM is good for getting some trace output of the performance of
your business logic "config saved", "motor started", "user
intervention timeout", ...
You pay extra for a ULINKpro just because it gives an additional
professional feature intending to cut down debug times when something
is really off and you can't just rely on single-stepping through the
program. Single-stepping doesn't work well in a real-time system
where the external hardware doesn't stop the time just because you
want to stop the time in the debugger.
So ETM is in some ways a flight data recorder (black box) crash
protected memory. Expensive but valuable.
Is anyone of you (who are reading this) using Ulinkpro?
ETM is only for instruction tracing or also used for DATA
Someone of KEIL technical persons said ETM is for instruction
trace and SWO(ITM) is for Data trace but in "Embedded Trace
ETMv1.0 to ETMv3.5 Architecture Specification", it is telling that
ETM is for both instruction trace and data trace. Which one is
In ULINKPro documentation there is given that accurate code
coverage and performance analyzing will be given by this Ulink pro
debugger. Code coverage and performance analyzer options are already
there in KEIL then what extra advantage this ULINKPro debugger is
I have started using SWO (Serial Wire output) which is serial wire
tracing. While I am trying this, it only showing the interrupt events
and hardfault handler events. Is this really meant for interrupts
tracing only. Other than these interrupt executions I couldn't see
Anyone of you please explain the different tracing options and
what are the reasons to go to next level.
Without ETM your debugger will never see any instruction trace
other than when using the simulator. And the simulator can't simulate
a full chip and may not know to add additional clock cycles when the
processor core stalls on some I/O or waiting for instructions from
With other options you may get some background reads of memory
content but then you need breakpoints and single-stepping to see what
the processor is doing.
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