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<h1>Librem 5 Dogwood Update</h1>
<p><b>Summary:</b><br>
We are almost at the end of the Dogwood board verification and
have found and fixed a number of issues with the initial
Dogwood boards. We believe we will be able to complete testing
and start shipping Dogwood phones out within a few weeks. We
have also been working on Evergreen in parallel to procure the
remaining components we need for mass production.</p>
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<p>We know the community is eager to hear any updates we might
have about the Librem 5. Like with our <a
href="https://puri.sm/posts/librem-5-birch-shipping-update-delay-of-just-a-few-days/">Birch</a>
and <a
href="https://puri.sm/posts/librem-5-chestnut-hardware-changes/">Chestnut</a>
updates, we are trying our best to give you correct
information for each batch with a reasonable level of
confidence without venturing into speculation or guesses.
This is especially important when it comes to reporting
hardware updates as it can take time and iterations to trace
down a problem into the component or mistake that caused it
and often first guesses for a root cause prove to be
incorrect.</p>
<p>Like everyone else we have been impacted by the COVID-19
pandemic and back in February we published an overall <a
href="https://puri.sm/posts/coronavirus-delays/">shipping
update</a> based on the best information we had at the
time including dates for Dogwood:</p>
<hr>
<ul>
<li>End of March: Librem 5 Dogwood internal hardware
revision for the Purism team</li>
<li>End of April: Librem 5 Dogwood batch for customer
pre-orders</li>
</ul>
<hr>
<p><a
href="https://social.librem.one/@purism/103968824971000879">We
started receiving the internal Dogwood hardware revision</a>
a bit later than expected in April and started the work to
test and verify the changes. As we mentioned in our <a
href="https://puri.sm/posts/breaking-ground/">Breaking
Ground</a> post, the Librem 5 is an entirely new phone
built from the ground up and that means significantly more
testing and tweaking than with an off-the-shelf design.
Unlike with Birch and Chestnut batches, which only had minor
tweaks on the previous batch based on problems we uncovered
during testing, Dogwood represented a much larger change–a
CPU flip to the other side of the PCB to help with heat
dissipation–that meant a full redesign of the PCB layout.</p>
<figure> <img
src="https://puri.sm/wp-content/uploads/2020/05/20200512_081030-1024x768.jpg"
alt="Dogwood PCB CPU side up"> <figcaption>Dogwood PCB
CPU side up</figcaption> </figure>
<p>We knew it would take longer to test Dogwood compared to
Birch and Chestnut and budgeted extra weeks for the tests
assuming we didn’t come across any major issues. Once
testing was complete we would apply any fixes and then send
out the remaining Dogwood batch to customers. Like with
Birch and Chestnut we wanted to bring you along for the ride
and give you updates as we have them, but up until now there
honestly hasn’t been all that much to report except that the
testing was in progress. This kind of testing of every
component in a long checklist is tedious work and is only
interrupted with a bit of excitement when something doesn’t
work as expected and you must drop everything to figure out
why.</p>
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<h2>Dogwood Hardware Fixes</h2>
<p>It's been about a month since we started that verification
and as expected we did find some issues with the initial
Dogwood boards. Overall the glitches we found have been minor
from a design and fix perspective such as an incorrect MOS FET
transistor part and a minor mistake in the CPU power supply,
but were glitches which resulted in odd and sometimes much
larger problems in the functionality of the device ranging
from damaging the USB section of the CPU in one case and
disabling an entire I2C bus in another! It’s taken more time
than expected to trace through these problems and then apply
and test fixes especially in the case of the CPU since it
required reworks in the PCB that were difficult to make on the
existing boards and new CPUs.</p>
<figure> <img
src="https://puri.sm/wp-content/uploads/2020/05/20200512_081019-1024x768.jpg"
alt="Dogwood PCB CPU side down"> <figcaption>Dogwood PCB
CPU side down</figcaption> </figure>
<p>Another system we have been looking into since Birch is GNSS
(aka GPS). GNSS is a pretty delicate thing, the GNSS satellite
signals are so weak, it’s like trying to spot an 80W light
bulb in orbit (that’s about the energy equivalent). What is
received on the ground here on earth is usually below the
noise level of the antenna and takes pretty significant signal
processing to get data from it. This means that the GNSS
antenna signal path must be pretty close to perfect.</p>
<p>Besides this with Chestnut we discovered that ST Micro, the
manufacturer of the TESEO LIV3 GNSS multi constellation
receiver we are using in the L5, silently changed the
recommendations for the antenna input electronics design. Now
in Dogwood we see that GNSS reception still wasn’t great so we
went back to suppliers and the drawing board, applied some
more changes and are now finally getting a fix!</p>
<p>Of course, <em>now</em> is the time to apply all of these
fixes, <em>before</em> we go into mass production. As you
might expect, changes are much more complicated with larger
volumes, which is why we chose the public small batch approach
to begin with and invited you to come along with us for this
ride. At this point we have successfully verified almost all
of the components with only a handful left to go and we feel
we are pretty close to being able to greenlight the remaining
Dogwood PCB production within a week so we can start shipping
a few weeks after that. While this has been going on we have
also been working in parallel on Evergreen to complete
procurement of the components we’ll need for mass production.</p>
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<h2>What's Next</h2>
<p>Now that we are almost to the end of Dogwood hardware
verification, soon we will be able to shift focus from
testing individual components on a PCB to evaluating Dogwood
and the CPU flip in particular as a whole. We know many
people are curious about the impact of the CPU flip on heat
dissipation and we intend to publish more detailed analysis
soon in a future update.</p>
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