[Testannounce] Librem 5 Dogwood Update

Fri May 15 14:15:33 PDT 2020

  Librem 5 Dogwood Update

*Summary:*
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.

We know the community is eager to hear any updates we might have about
the Librem 5. Like with our Birch
<https://puri.sm/posts/librem-5-birch-shipping-update-delay-of-just-a-few-days/>
and Chestnut <https://puri.sm/posts/librem-5-chestnut-hardware-changes/>
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.

Like everyone else we have been impacted by the COVID-19 pandemic and
back in February we published an overall shipping update
<https://puri.sm/posts/coronavirus-delays/> based on the best
information we had at the time including dates for Dogwood:

------------------------------------------------------------------------

  * End of March: Librem 5 Dogwood internal hardware revision for the
    Purism team
  * End of April: Librem 5 Dogwood batch for customer pre-orders

------------------------------------------------------------------------

We started receiving the internal Dogwood hardware revision
<https://social.librem.one/@purism/103968824971000879> a bit later than
expected in April and started the work to test and verify the changes.
As we mentioned in our Breaking Ground
<https://puri.sm/posts/breaking-ground/> 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.

Dogwood PCB CPU side up Dogwood PCB CPU side up

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.

    Dogwood Hardware Fixes

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.

Dogwood PCB CPU side down Dogwood PCB CPU side down

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.

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!

Of course, /now/ is the time to apply all of these fixes, /before/ 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.

    What's Next

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.

Purism

Thanking you for your support,
— the Purism team (feedback at puri.sm)

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