How to Debug Embedded Designs with an Oscilloscope

Embedded designs consist of multiple
serial protocols and components that require deeper analysis. Learn how to
fully characterize your embedded or mixed-signal designs to find any errors
that could disrupt your device’s performance. Hi I’m Erin east with
Keysight and in this video you’ll learn how to test and debug your embedded
designs. This includes protocol triggering and decoding for I squared C,
SPI, UART/RS-232, I squared S, and USB PD, also known as USB power delivery. The
primary reason you should use an oscilloscope to debug and characterize
embedded serial buses is because of an oscilloscope’s inherent ability to
characterize the analog quality of the signal. It also allows you to time
correlate serial activity with other analog and digital i/o signals in your
design. Today’s embedded designs based on
microcontrollers and digital signal processors often include a combination
of real-world analog signals, digital i/o buses, and serial buses.
Although microcontrollers and DSPs are often thought of as simply digital
control and processing devices, most MCUs and DSPs today are mixed signal
devices. I squared C, SPI and UART/ RS-232 are often used for chip-to-chip
communication between MCUs and memory chips as well as other peripherals.
There are many helpful capabilities in the Infiniivision oscilloscopes that
allow you to debug easier and faster like the hardware based serial decoding
for responsiveness, the dual bus time interleave protocol lister display,
digital channels from mixed signal analysis, the ability to capture a long
time span of packets in detail with segmented memory, and a real time frame
error counter. You can test all buses in your embedded design and mixed signal
designs with the Infiniivision embedded software package. This also allows you to
perform pass/fail mask testing, frequency response analysis,
and enhance HDTV video triggering. I mentioned the hardware-based
decoding. this is contrary to the software decoding that you’ll find in
other oscilloscopes from other vendors. Because there’s a dedicated hardware
component for the serial decoding, you’re basically decoding in real time. There’s
no lag and responsiveness like what you would see with software decoding from
other vendors. Hardware decoding is significantly faster and this means that
you’re more likely to capture rare errors and random glitches. So let’s take
a look at the scope and how to set up serial decoding. This setup process is
generally the same for every type of serial bus. To start out of course you
have to probe on your device. Right now I’m probing on an I squared C bus and
it’s clock, but we see there’s no decoding on-screen and we don’t have a
stable trigger. First and foremost you have to tell the oscilloscope you want
to perform serial decoding. Cnce you have serial turned on, set the mode to
whichever bus type you’re decoding. Notice in the decoding bar the data is
in various colors and formats. If you hold down the mode button you can
see the meanings of each of those symbols, hex values, or colors. Next define
the signal that you’re trying to decode. In this case I mentioned we’re working
with a serial clock and the I squared C data. To enable the I squared C trigger
and decoding along with other embedded buses and analysis options you can
download the free trial of the embedded software package from the website linked
on screen or in the description. So now that we’re all set up to decode that
serial bus we have to set a stable trigger. To trigger on various events
within the bus, turn on the serial trigger and choose what to trigger on.
Depending on the trigger you select specify the address or the data that you
wish to analyze further and note that you can actually use the zone triggering
capability to isolate various parts of the serial bus as well. So now we have a
very stable trigger and can analyze the data in each packet. The lister allows
you to navigate through each packet or strings of packets with details on
timing, the address, and the data. If you have to further analyze specific trigger
events or packets the standard segmented memory
capability can be used to capture up to a thousand events. This can be done with
any serial mode including those on the digital MSO channels. So let’s look at
this 4-wire SPI decode with the trigger set on the MOSI and MISO data.
Using segmented memory we’ve captured 600 trigger events. By scrolling through
each event in the Lister or sidebar you can see the MOSI and MISO data. Each
click on the different Lister row or timestamp will show that specific
section of the data on-screen including the decode information. To learn more
about what segmented memory is and how to set it up
check out my What is Oscilloscope Segmented Memory video on our Keysight
Labs YouTube channel. Also remember that you can probe your mixed signal designs
as well and view both the digital and analog signals at the same time. Doing so
turns your oscilloscope into an MSO: a mixed signal oscilloscope. An MSO is a
hybrid test instrument that combines the measurement capabilities of a digital
storage oscilloscope, a DSO, with the important aspects of a logic analyzer or
serial protocol bus analyzer. This means that you can view up to 4 analog signals
and 16 digital signals simultaneously. And this is all being done in hardware,
so the update rate remains uncompromised. You’ll continue to see an incredibly
fast response of up to a million waveforms per second. On most other
oscilloscopes with software decoding turning on these digital channels will
cause your update rate to drop significantly causing you to miss
important signal events. And lastly you can also simultaneously analyze two
types of serial buses using the dual bus time interleaved decoding. To initiate
this you simply turn on two serial bus types when you’re setting up the serial
options. Set up each bus to the specified mode and set your trigger. With this you
can see if a bus is triggering the appropriate events in another bus or you
can view the timing of events between two buses. I also mentioned that the
embedded software package enables a few advanced analysis capabilities as well
such as mask testing, frequency response analysis, and
HDTV video triggering. If you need to validate the quality and stability of
your components or systems the mask testing capability can save you time and
provide pass/fail statistics almost instantly. Mask testing offers a fast and
easy way to test your signal to specified standards as well as the
ability to uncover unexpected signal anomalies such as glitches. Mask testing
on other oscilloscopes is usually based on software intensive processing
technology which tends to be slow. Much like the software decoding that you
learned about. With mask testing being performed in hardware on the
Infiniivision oscilloscopes you can test up to two hundred and seventy thousand
real-time waveform pass/fail tests per second. This makes your testing
throughput orders of magnitude faster than what you could achieve on other
oscilloscopes software mask testing. The creation of the mask is simple with the
auto mask function or the option to upload custom masks. You can also
download multi-region masks and setup based on your industry standards from
our website. Frequency response analysis or FRA is often a critical measurement
used to characterize the frequency response of a variety of today’s
electronic designs including passive filters, amplifier circuits, and negative
feedback networks in switch mode power supplies or the loop response. The
frequency domain measurement capability is achieved with a swept gain and phase
measurement versus frequency. This is also known as a bode plot. The Infiniivision oscilloscope uses the scope’s built-in waveform generator to simulate the
circuit under test at various frequency settings and then it captures the input
and output signals using two channels of the oscilloscope. At each test frequency
the scope measures, computes, and plots the gain logarithmically and the phase
linearly. And lastly whether you’re debugging consumer electronics with HDTV
or characterizing a design the enhanced HDTV video triggering and analysis
provides support for a variety of HDTV standards.
This enhanced video measurement capability supports a video IRE display
grid with cursor measurements performed in the video IRE units for NTSC and
PAL standards. In addition enhanced video analysis provides an array of additional
HDTV triggering standards that will help you speed up debug and characterization.
You can see how the plethora of embedded decodes and analysis capabilities enable
you to fully characterize your embedded and mixed signal designs. Using functions
like the segmented memory, the MSO options, and dual bus time interleaved
decoding you’re able to analyze various events simultaneously. Furthermore you
can analyze the other components of your embedded design such as the switch mode
power supply or any filters with the Keysight infiniivision exclusive
frequency response analysis capability. The unmatched hardware-based mask
testing and segmented memory capabilities allow you to dive even
deeper into the analysis. Download a free trial of the Infiniivision embedded
software package that goes with your oscilloscope and learn more about it by
checking out the link on screen or in the description. As always place any
questions in the comments section below and stay up to date with the latest
how-to videos by clicking subscribe on our YouTube channel and following us on
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