Do you have some suggestions?
Do you have some suggestions?
Today I found that SWDIO signal isn't able to swing normally between GND
and VDD on broken MCUs. I suspect something bad occurred inside the MCU,
but it's strange it happened on three different boards with three
different MCUs.
Could it be ESD?
Il 23/06/2022 23:38, pozz ha scritto:
Do you have some suggestions?
Today I found that SWDIO signal isn't able to swing normally between GND
and VDD on broken MCUs. I suspect something bad occurred inside the MCU,
but it's strange it happened on three different boards with three
different MCUs.
Could it be ESD?
Or maybe some ground loops, for example if you have connected the J-Link
probe to a desktop PC (or in general a PC not isolated from mains) and your >> boards are somewhat connected to mains or earth ground too.
Yes, I use a desktop PC connected to mains and the boards are supplied
from an AC/DC connected to mains too.
Is this a problematic scenario?
On 24/06/2022 11:25, pozz wrote:
Il 23/06/2022 23:38, pozz ha scritto:
Do you have some suggestions?
Today I found that SWDIO signal isn't able to swing normally between
GND and VDD on broken MCUs. I suspect something bad occurred inside
the MCU, but it's strange it happened on three different boards with
three different MCUs.
Could it be ESD?
I don't know these particular microcontrollers in detail, but there are
two things that can cause problems with debugging that I can think of.
One is that you can often re-use the pin as a GPIO. If your program
re-uses the debug pins as GPIO, then maybe this is happening before the debugger can get access. The debugger should be able to fix this if it
has access to a hard reset pin, but some setups are missing that.
The other is that sometimes you can disable the debugger for security reasons. I've done that by accident on a microcontroller (an AVR, IIRC).
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on), short-circuits
when trying to use an oscilloscope probe with clumsy fingers, etc. If
you have access to an X-Ray machine, you might be able to get some idea
about what happened.
Un bel giorno pozz digitò:
Do you have some suggestions?
Today I found that SWDIO signal isn't able to swing normally between GND
and VDD on broken MCUs. I suspect something bad occurred inside the MCU,
but it's strange it happened on three different boards with three
different MCUs.
Could it be ESD?
Or maybe some ground loops, for example if you have connected the J-Link probe to a desktop PC (or in general a PC not isolated from mains) and your boards are somewhat connected to mains or earth ground too.
Note that laptops with the charger plugged in are not perflectly isolated from mains either. I've experienced noise problems in several occasions
with JTAG probes connected to laptops with the charger plugged in. The
noise disappeared just by unplugging the charger.
Un bel giorno pozz digitò:
Or maybe some ground loops, for example if you have connected the J-Link >>> probe to a desktop PC (or in general a PC not isolated from mains) and your >>> boards are somewhat connected to mains or earth ground too.
Yes, I use a desktop PC connected to mains and the boards are supplied
from an AC/DC connected to mains too.
Is this a problematic scenario?
Normally it shouldn't be, but it also depends on what the board does. If it contains some power stages running at high frequency, it is quite common (especially if the EMI filtering is subpar) that switching currents can
pass through the AC/DC power supply and create problems.
If this keeps happening, try using a laptop isolated from mains and see if
it helps.
If this keeps happening, try using a laptop isolated from mains and see if >> it helps.
I hate laptop as development machine, I will try some USB and/or
debugger isolator. However I imaging the problem would arise with oscilloscope, UART/USB converter and so on.
Un bel giorno pozz digitò:
Or maybe some ground loops, for example if you have connected the J-Link >>> probe to a desktop PC (or in general a PC not isolated from mains) and your >>> boards are somewhat connected to mains or earth ground too.
Yes, I use a desktop PC connected to mains and the boards are supplied
from an AC/DC connected to mains too.
Is this a problematic scenario?
Normally it shouldn't be, but it also depends on what the board does. If it contains some power stages running at high frequency, it is quite common (especially if the EMI filtering is subpar) that switching currents can
pass through the AC/DC power supply and create problems.
If this keeps happening, try using a laptop isolated from mains and see if
it helps.
On 24/06/2022 16:42, dalai lamah wrote:
Un bel giorno pozz digitò:
Or maybe some ground loops, for example if you have connected the
J-Link
probe to a desktop PC (or in general a PC not isolated from mains)
and your
boards are somewhat connected to mains or earth ground too.
Yes, I use a desktop PC connected to mains and the boards are supplied
from an AC/DC connected to mains too.
Is this a problematic scenario?
Normally it shouldn't be, but it also depends on what the board does.
If it
contains some power stages running at high frequency, it is quite common
(especially if the EMI filtering is subpar) that switching currents can
pass through the AC/DC power supply and create problems.
If this keeps happening, try using a laptop isolated from mains and
see if
it helps.
Another trick is to make sure you have a separate ground connection
between the board and the PC before attaching the JTAG. A wire from the board ground to the PC's case is usually fine.
Il 24/06/2022 14:15, David Brown ha scritto:
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on), short-circuits
when trying to use an oscilloscope probe with clumsy fingers, etc. If
you have access to an X-Ray machine, you might be able to get some idea
about what happened.
I admit I don't have professional workbench with anti-static writ strap
band and so on, but I worked for many years without these kind of
problems. It's strange I encountered so many problems concentrated in a
few weeks.
I will understand the problem of ground loops.
On 2022-06-24 pozz wrote in comp.arch.embedded:
Il 24/06/2022 14:15, David Brown ha scritto:
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on), short-circuits
when trying to use an oscilloscope probe with clumsy fingers, etc. If
you have access to an X-Ray machine, you might be able to get some idea
about what happened.
I admit I don't have professional workbench with anti-static writ strap
band and so on, but I worked for many years without these kind of
problems. It's strange I encountered so many problems concentrated in a
few weeks.
I will understand the problem of ground loops.
Anti-static measures will not help for any of the problems David
describes. But they will prevent damage from ESD. Which could also be a source for your problem.
Has the weather been very dry in those problem weeks? Or did you change
your floor or did you get new shoes?
My experience with ESD damage is that it is often subtle - it leads to long-term reliability issues, rather than outright failures. So the
production department at my company is extremely careful about ESD. Up
in the development department, we can be a bit laxer as long as the
devices are not going to customers (or at least, not going further than
the customers' development departments).
I can't remember ever having a
failure that I could definitely attribute to ESD damage in my lab, while
I have definitely solved reliability problems by extra ground connections.
Mind you, I would still avoid woollen slippers on a nylon carpet!
On 2022-06-24 David Brown wrote in comp.arch.embedded:
My experience with ESD damage is that it is often subtle - it leads to
long-term reliability issues, rather than outright failures. So the
True, only large discharges will have an immediate effect. And you will probably have felt the spark.
production department at my company is extremely careful about ESD. Up
Same here. Conductive floors and no access in certain areas without conductive shoes or conductive straps in normal shoes.
in the development department, we can be a bit laxer as long as the
devices are not going to customers (or at least, not going further than
the customers' development departments).
Also very recognizable. ;-)
We do have ESD matts on most work tables, but wrist straps are seldomly
worn. Floors on development are not conductive, but not static as well.
Have never felt a discharge on touching stuff there.
I can't remember ever having a
failure that I could definitely attribute to ESD damage in my lab, while
I have definitely solved reliability problems by extra ground connections.
I think I had such an incident in my home office before I changed the
floor. With certain footware on the old floor I'd spark all over the
place in dry conditions. Irritating and not good for the equipment.
Mind you, I would still avoid woollen slippers on a nylon carpet!
Laminate flooring and some plastic shoe soles are also a no-no.
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on), short-circuits
when trying to use an oscilloscope probe with clumsy fingers, etc. If
you have access to an X-Ray machine, you might be able to get some idea
about what happened.
I admit I don't have professional workbench with anti-static writ strap
band and so on, but I worked for many years without these kind of
problems. It's strange I encountered so many problems concentrated in a
few weeks.
I will understand the problem of ground loops.
On 24/06/2022 16:42, dalai lamah wrote:
Un bel giorno pozz digitò:
Or maybe some ground loops, for example if you have connected the
J-Link
probe to a desktop PC (or in general a PC not isolated from mains)
and your
boards are somewhat connected to mains or earth ground too.
Yes, I use a desktop PC connected to mains and the boards are supplied
from an AC/DC connected to mains too.
Is this a problematic scenario?
Normally it shouldn't be, but it also depends on what the board does.
If it
contains some power stages running at high frequency, it is quite common
(especially if the EMI filtering is subpar) that switching currents can
pass through the AC/DC power supply and create problems.
If this keeps happening, try using a laptop isolated from mains and
see if
it helps.
Another trick is to make sure you have a separate ground connection
between the board and the PC before attaching the JTAG. A wire from the board ground to the PC's case is usually fine.
On 2022-06-24 pozz wrote in comp.arch.embedded:
Il 24/06/2022 14:15, David Brown ha scritto:
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on), short-circuits
when trying to use an oscilloscope probe with clumsy fingers, etc. If
you have access to an X-Ray machine, you might be able to get some idea
about what happened.
I admit I don't have professional workbench with anti-static writ strap
band and so on, but I worked for many years without these kind of
problems. It's strange I encountered so many problems concentrated in a
few weeks.
I will understand the problem of ground loops.
Anti-static measures will not help for any of the problems David
describes. But they will prevent damage from ESD. Which could also be a source for your problem.
Has the weather been very dry in those problem weeks? Or did you change
your floor or did you get new shoes?
Il 24/06/2022 20:29, Stef ha scritto:
On 2022-06-24 pozz wrote in comp.arch.embedded:
Il 24/06/2022 14:15, David Brown ha scritto:
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on), short-circuits >>>> when trying to use an oscilloscope probe with clumsy fingers, etc. If >>>> you have access to an X-Ray machine, you might be able to get some idea >>>> about what happened.
I admit I don't have professional workbench with anti-static writ strap
band and so on, but I worked for many years without these kind of
problems. It's strange I encountered so many problems concentrated in a
few weeks.
I will understand the problem of ground loops.
Anti-static measures will not help for any of the problems David
describes. But they will prevent damage from ESD. Which could also be a
source for your problem.
Has the weather been very dry in those problem weeks? Or did you change
your floor or did you get new shoes?
Very dry? On the contrary, now and here we have humid air at least
respect other periods of the year.
No change in floor or shoes.
On Fri, 24 Jun 2022 16:25:55 +0200, pozz wrote:
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on), short-circuits
when trying to use an oscilloscope probe with clumsy fingers, etc. If
you have access to an X-Ray machine, you might be able to get some idea
about what happened.
I admit I don't have professional workbench with anti-static writ strap
band and so on, but I worked for many years without these kind of
problems. It's strange I encountered so many problems concentrated in a
few weeks.
I will understand the problem of ground loops.
Take the exact setup and before plugging the debugger measure the voltage between the CPU board ground and the debugger ground with a multi meter
in AC mode. My guess is that you have stray AC (mains) voltage on either
side (by Y-caps in a PSU or just capacitive coupling over the transformer
to the DC side GND). These stray voltages often reach 50% of AC voltage,
in you case probably 60V-AC. When you plug the connector they might
easily kill a CPU port.
Il 24/06/2022 18:26, David Brown ha scritto:
On 24/06/2022 16:42, dalai lamah wrote:
Un bel giorno pozz digitò:
Or maybe some ground loops, for example if you have connected the
J-Link
probe to a desktop PC (or in general a PC not isolated from mains)
and your
boards are somewhat connected to mains or earth ground too.
Yes, I use a desktop PC connected to mains and the boards are supplied >>>> from an AC/DC connected to mains too.
Is this a problematic scenario?
Normally it shouldn't be, but it also depends on what the board does.
If it
contains some power stages running at high frequency, it is quite common >>> (especially if the EMI filtering is subpar) that switching currents can
pass through the AC/DC power supply and create problems.
If this keeps happening, try using a laptop isolated from mains and
see if
it helps.
Another trick is to make sure you have a separate ground connection
between the board and the PC before attaching the JTAG. A wire from
the board ground to the PC's case is usually fine.
Sorry I don't follow very well these arguments.
You say to have a separate ground connection between the board and the
PC, but you suggest to connect a wire between them. It seems
contradictory to me.
What do you mean with board ground? GND, the reference voltage for 3.3V
of the MCU?
Usually I work on boards with only one low-voltage power
supply input (12Vdc, plus and minus) that is down-scaled to 3.3V by a
DC/DC switching regulator. There isn't an *earth* connection on the
board. Mounting holes are connected to GND, but most of the time, the
board is not mounted on my bench.
Il 26/06/2022 16:25, Reinhardt Behm ha scritto:
On Fri, 24 Jun 2022 16:25:55 +0200, pozz wrote:
Of course you could always have had damage from ground loops, spikes
when plugging the debugger in and out (if power is on),
short-circuits when trying to use an oscilloscope probe with clumsy
fingers, etc. If you have access to an X-Ray machine, you might be
able to get some idea about what happened.
I admit I don't have professional workbench with anti-static writ
strap band and so on, but I worked for many years without these kind
of problems. It's strange I encountered so many problems concentrated
in a few weeks.
I will understand the problem of ground loops.
Take the exact setup and before plugging the debugger measure the
voltage between the CPU board ground and the debugger ground with a
multi meter in AC mode. My guess is that you have stray AC (mains)
voltage on either side (by Y-caps in a PSU or just capacitive coupling
over the transformer to the DC side GND). These stray voltages often
reach 50% of AC voltage, in you case probably 60V-AC. When you plug the
connector they might easily kill a CPU port.
I made the measure you suggested and I found around 20Vac between
debugger GND and board GND *before* plugging them.
After adding a good wire connection between PC metallic case (near a
mounting screw) and board GND, the Vac measured goes near to zero.
Could it be this the cause of issues I observed? I will continue with
this connection and see.
Thank you for your suggestions.
On Mon, 27 Jun 2022 10:07:37 +0200, pozz wrote:
Il 26/06/2022 16:25, Reinhardt Behm ha scritto:
On Fri, 24 Jun 2022 16:25:55 +0200, pozz wrote:
Of course you could always have had damage from ground loops, spikes >>>>> when plugging the debugger in and out (if power is on),
short-circuits when trying to use an oscilloscope probe with clumsy
fingers, etc. If you have access to an X-Ray machine, you might be >>>>> able to get some idea about what happened.
I admit I don't have professional workbench with anti-static writ
strap band and so on, but I worked for many years without these kind
of problems. It's strange I encountered so many problems concentrated
in a few weeks.
I will understand the problem of ground loops.
Take the exact setup and before plugging the debugger measure the
voltage between the CPU board ground and the debugger ground with a
multi meter in AC mode. My guess is that you have stray AC (mains)
voltage on either side (by Y-caps in a PSU or just capacitive coupling
over the transformer to the DC side GND). These stray voltages often
reach 50% of AC voltage, in you case probably 60V-AC. When you plug the
connector they might easily kill a CPU port.
I made the measure you suggested and I found around 20Vac between
debugger GND and board GND *before* plugging them.
After adding a good wire connection between PC metallic case (near a
mounting screw) and board GND, the Vac measured goes near to zero.
Could it be this the cause of issues I observed? I will continue with
this connection and see.
Thank you for your suggestions.
It could not only be, it will be. Imagine you plug the connector, GND is
not contacted first, then the CPU pin sees 20V-AC. That means +20V*sqrt(2) relative to CPU-GND and -20V*sqrt(2). That is far out of spec. It will
kill the pin.
I had something similar. A colleague had used a 2 wire extension cord for
a soldering station, so no earth connection. I did not know this and
killed the reset input of my controller. When I found out this I
understood why we had several cases of non-functioning boards. The two
wire extension cord was 2$ cheaper than a 3 wire cored. the cost of this "saving" was several 100$.
Anyway in my case the power cord of my PC is connected to a UPS and the
AC/DC that powers the board is connected to earth connection of the grid.
Working with two wires power cords is risky and I learned that in the past.
However this isn't the case now, both PC and board have a good 3-wires
power connection, but there's a 20Vac voltage between the grounds.
On 2022-06-27 pozz wrote in comp.arch.embedded:
Anyway in my case the power cord of my PC is connected to a UPS and the
AC/DC that powers the board is connected to earth connection of the grid.
Working with two wires power cords is risky and I learned that in the past. >>
However this isn't the case now, both PC and board have a good 3-wires
power connection, but there's a 20Vac voltage between the grounds.
With both grounded, there cannot be a 20VAC voltage between the grounds. (unless there is an extreme amount of current ofcourse, but that will
not be the case)
Your PC is a standard desktop?
Then the 0V is connected to the earth
connection of the power plug. This is not the case if you have a laptop.
The supply will have an earth connection, but the DC output is floating.
Your AC/DC probably has a similar construction as a laptop supply: Earth connection on the power plug and a floating DC output.
That there still is a measurable voltage is because of capacitive
coupling in the AC/DC between AC input and DC output (assuming PC is
really grounded). The voltage you measure depends on the impedance of
that coupling and the impedance of your meter.
Just measured 0V to earth on a few supplies here with a volt meter with
input impedance of > 10 MOhm / < 100 pF:
Recent 150W lab supply: 15 mVAC
Old analog 2x40W supply: CH1: 15VAC, CH2: 5 VAC
Recent 10W switching wall wart: 90VAC
Tried to measure short circuit currents as well, but that was not very reliable as I don't have an AC uA meter here. Currents are too small.
As the current is very low, this should give no problems. There could be
a small surge if you just happen to connect at the peak of that AC
voltage. But the capacitance behind that should be very low, otherwise
the voltage/current measurements should be different. (Haven't drawn out
the resulting schematic and the consequences though).
So you could do a current measurement between the grounds. I would
expect less than 0.1 mA AC there.
But with an isolated supply there also is a chance of static (DC)
buildup. Depending an the capacity to earth this could give and ESD
discharge on connection.
So all this may not be your problem, but connecting an additional earth between PC and your supply will not hurt anyway. And it has the (small) possibility of solvng your problem.
Il 28/06/2022 11:23, Stef ha scritto:
On 2022-06-27 pozz wrote in comp.arch.embedded:
Anyway in my case the power cord of my PC is connected to a UPS and the
AC/DC that powers the board is connected to earth connection of the grid. >>>
Working with two wires power cords is risky and I learned that in the past. >>>
However this isn't the case now, both PC and board have a good 3-wires
power connection, but there's a 20Vac voltage between the grounds.
With both grounded, there cannot be a 20VAC voltage between the grounds.
(unless there is an extreme amount of current ofcourse, but that will
not be the case)
The PSU of desktop PC and AC/DC of board are connected to the earth conductor, i.e. I'm using 3-wires power cord.
But their separate GND aren't connected.
Your PC is a standard desktop?
Yes.
Then the 0V is connected to the earth
connection of the power plug. This is not the case if you have a laptop.
The supply will have an earth connection, but the DC output is floating.
No, it's a desktop PC, not a laptop.
I don't know why I have 20Vac between GND of J-Link and board.
Maybe the problem is in the UPS that has some failure.
Your AC/DC probably has a similar construction as a laptop supply: Earth
connection on the power plug and a floating DC output.
Yes, but I connect GND (0V of DC output) to earth.
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