CE Pro May 2023 - 20

Networking+Home Control
HDMI CORNER by DPL Labs
Link Training Testing for
Cables Gets Underway
LINK TRAINING is a support
feature that is now included
in the new HDMI 2.1a
specification. We reported
on this back in July 2020's
CE Pro (page 24) to provide
some base for this new
feature and how it can offer
a way for cables to adapt to
lower data rates. It is used
to keep digital video systems
functional without the fear
of going into the dark due
to any cable inconsistencies
in performance. It is a direct
feedback system between a
source and a display device.
Fig. 1 depicts a flow chart on
how this works.
The process begins at
LTS:1. Here a determination
is made on whether
the signal is Legacy TMDS
or Current FRL. If TMDS is
determined, an interrupt
occurs and diverts to Legacy
TMDS. If not, then Link
Training moves into action
at LTS:2 and prepares the
system to start Link Training.
Arriving at LTS:3 initiates
the Link Training Process.
Here a series of patterns and
report flags are used to judge
signal performance. If signal
performance will not satisfy
the source and display's negotiated
resolution data rate,
LTS:3 reports this to LTS:4.
LST:4 then reduces the data
rate in an effort to satisfy the
negotiated EDID between
the source and display.
After all decisions have
20 | CE Pro May 2023
been made, LTS:3 reports to
LTS:P (Pass). If signal integrity
cannot be overcome, Link
Training will take the signal
and force it to low-quality
legacy TMDS LTS: L. The
process is now complete.
This is all good, except for
the fact that the customer
must be satisfied with a
lower-quality video that
they may have paid for in
their so-called state-of-theart
system. Link Training
cannot be turned off. What
determine each cable's published
transmission data rate
performance limits, similar to
the way Link Training does.
This took almost two years
to build, test, debug and
complete. DPL is proud to
say we have completed this
important new addition to
the 48G Reference Standard
Platform and have entered
into service this month.
How is it done? The process
entails a series of calculations
within the digital
This process gets repeated
over a predetermined
number of runs establishing
a pattern of consistency. If
the cable under test passes
this process, then a monitoring
process is initiated
watching for any breaches
to the signal's eye-opening.
Now with this new set of
numbers, DPL can calculate
a set of limits guaranteeing
the cable's published transmission
bit rate throughput,
thereby eliminating the
The graphic illustrates a flow chart on the interface's feedback process between a source
and a display device.
it is, is what you get.
Since the announcement
of Link Training, DPL
Labs has put a considerable
amount of effort into
building an additional test
application to its 70+ existing
test functions residing
in DPL Labs' 48G Reference
Standard Platform. It will
video signal's Eye Diagram.
Here our new instrumentation
team ran hundreds of
scenarios pushing the test
limits to near-perfect accuracy.
By incremental stress
mapping each eye diagram
the instrument determines
the cable's maximum transmission
data rate.
need for Link Training to
reduce video performance
due to cable integrity. This
will provide peace of mind
for your customers.
JEFF BOCCACCIO,
president of DPL Labs, can
be reached at info@dpllabs.
com, or visit dpllabs.com.
cepro.com
http://www.dpllabs.com http://www.cepro.com
CE Pro May 2023

Table of Contents for the Digital Edition of CE Pro May 2023
