X-Post from r/linux: An electrical engineers opinion on the Librem 5

I don’t think he misunderstood. He actually raised a serious concern and tried to show the only way out which he saw - and that is optimizing firmware.

And the powerconsumption is surely not exaggerated. Radio emission costs a lot of energy - I always wondered how they managed to keep the consumption so low. Perhaps you remember early cell-phones? They had a battery back attached, which you would carry with you like a suitcase :slight_smile:

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As far as I know, Purism had not work on modem firmware, they use proprietary software provided with the hardware.

The redditer says:

I suspect Purism employees have spent most of their time getting the modem firmware and RF-fronted SW into a functional state. There was a blog post somewhere where a Purism employee brought up a call over the air (OTA). I can’t find it but that was by far the most important milestone of their effort. Getting past RACH and acquiring a base-station OTA is huge in the industry.

Yeah trip about this too. But i think he means that purisms firmware team is using the closed blob firmware from the vendor.
And with that figures out to get it in a working state on the librem 5, which acknowledge as important milestone, and then try to power optimise it with the parameters the closed blob and the librem 5 firmware gives them.

I don’t think he misunderstood that purism has no access to the binary blob. He seam to knowledge about the topic.


Exactly! It was a very pleasant read on reddit for once :slight_smile: When all is said and done it will be interesting to learn how many decisions regarding these considerations came down to economic reasons. Well, we are in the “first generation” stage and, as it goes, I wish more for those who come after me :slight_smile:


I understand his concern but I am not sure if all of his assumptions are accurate.

First, his point is that IoT devices are not power optimized. I am not sure if this is the case as IoT is more than just vending machines but also battery powered toys and all kind of things. I would rather say that IoT is power optimized but for a different use case. It is supposed to be very power efficient while idling around and waiting for either some user or sensor input and then send a short burst of data (or getting triggered by a control instance). He is probably write that in general IoT modems are not optimized for a low power usage while transferring huge amounts of data (which is the consumer / our use case). Somehow proving this it the part Gemalto writes about their card in the public datasheet:

IoT Optimized Power Management
An advanced power management system delivers fast shut down and
wake up capabilities helping while an intelligent single-sided design
improves heat dissipation and extends battery power making it ideal for
remote applications with wide temperature ranges.

His second assumption is that Gemalto and Broadmobi are actually the modem manufacturers. I am not sure if this is the case. They for sure design and manufacture the card but not necessarily the IC within the card (which is the real modem). The whole mobile modem market is owned by a couple of large companies (the ones he names in his post) and mostly their modems are used internally in such cards. A quick search for the Broadmobi card brought up the FCC page for their card (here) and the pictures of the card without the metal cap looks like if they use a Qualcomm modem (MDM9607). This is still an IoT optimized modem but from Qualcomm and not some smaller company (so maybe its optimized for power similar to the consumer modem versions). Similar Gemalto has a press release stating:

Based on the latest long life LTE chipset from Qualcomm Technologies, the PLS8 delivers industry-leading LTE multiband support for seamless connectivity to the fastest networks worldwide.

Especially with the second point I am not sure if his conclusions about the reception and power hold. For example his point on interoperability. He is right that the big modem manufactures test a lot, but since I assume that at least the Broadmobi card uses a Qualcomm modem I believe this is the case for this modem.

An other point he raises is the SNR and that he does not believe that its a problem of the antenna placement. He is right that the plastic back does not interfere strongly with any antenna in the case. But in Todds disassembly video he says that the antennas are currently taped to the metal frame and it looks like they are in between the frame and the battery. And this is certainly a non ideal placement and surely can degrade the SNR. So maybe Todd is right and the reception issues can be fixed in placing the antennas directly below the plastic back. I am also not sure if I agree with him that IoT devices always have a good radio channel (and so a high SNR) and do not need to focus on low SNR situations. A lot of the applications for IoT are also very remote where the maximum distance to the base station plays a big role (thats why they often do not use LTE but systems like LoRa). But IoT is really just a buzz word and not well defined, so its hard to argue with facts here.

I also agree with Torrone, Pursim did not work on the mobile communication part except picking the modem cards, extending the modem manager software for gnome (but for the actuall interface to the card and not the mobile part, thats all handled in the m.2 card/modem IC) and placing/picking/designing the antennas. I do not think they have any influence on the points mentioned by the redditer accept choosing different cards. I also think he overestimates Purisms influence on the firmware. If I understood correctly the firmware is stored in the m.2 card and not somewhere accessible.

And thats the main issue, I am not sure if Purism has actually a chance to select different cards meaning non IoT cards. Most consumer modems are not sold as m.2 cards but only as chips (and often combined with the main CPU). If I remember the thread about alternative m.2 cards correctly, nearly all options mentioned there where cards very similar to the PLS8 or BM818. So if Purism (and us) want exchangeable cards for the mobile connection with the binary blob completely separated form the main CPU, there might not be an other option than what we have now. And that means we have to live (or stay with Android and the likes) with potential drawbacks like higher power consumption / bad reception. But maybe the drawbacks are not as bad as he believes.

But hey, maybe someone finds a m.2 LTE customer/smartphone grade card. In this case we just swap all our cards and the problems are solved, thats the advantage of the modular approach :slight_smile:

As a footnote, I am also a electrical engineer and work in the mobile communication domain in research. I do hardware (RF) and system design (signal processing…). So my background seems to be very similar to the redditer.

I would answer on reddit, but I do not have an account…

edit: added a Gemalto statement about using Qualcomm chips


I think that’s not quite correct. The choice of usable modems was narrowed down by

  • voice call capability
  • ability to run without runtime-loaded firmware (blobs)

But as I understand it, Purism is not just using M.2 cards “as available on the market”. They are working with the manufacturers to make changes and improvements to the firmware and drivers.


For getting rid of the runtime firmware we invested significantly in a custom firmware that the manufacturer made specifically for our use case.

And here, I believe, comes into play what Todd calls leverage: Very much depending on the order quantities, we might see improvements in several areas. Security, energy management, customizability, even openness.
I’m not suggesting we’ll see a fully free firmware any time soon (too many patents etc.), but to me at least it would not sound unreasonable to have an open firmware that embeds some IP cores. Maybe not, I don’t want to wake false hope :wink:

The point is, they do work with the manufacturers and the more leverage they have, the “better” the firmware will become.


I think the custom firmware part is about the WiFi card and not the mobile communication card (LTE). They certainly work with Redpine on the WiFi card (as can be seen in the librem5 source repos) but I have not seen anything about a collaboration with Gemalto or Broadmobi. Maybe @nicole.faerber or someone else form Pursim can comment on that.

edit: if they work on the firmware for the LTE modem (especially in the firmware part the redditer talks about) they do not only have to collaborate with Gemalto/Broadmobi but also with Qualcomm which might be a harder task (speaking of leverage compared to their overall business size).


I am also an Electrical Engineer who works with pre-release integrated circuits on a daily basis. When I ordered this phone from Purism, I pretty much expected the phone to be released in its current state (although expecting better communications from Purism). The task that Purism has taken-on is almost unbelievable in scope. I didn’t expect complete success, just a worthy step in the right direction. With that being said, the article does accurately point out the areas that I predicted (and that any EE would predict) when it comes to the technical challenges of releasing an open sourced smart phone which is (despite a successful fundraising campaign) still relatively unfunded.

As the business model for the Librem 5 is unique, so will the development process of it need to be unique. If you set out to build a low-volume (relatively home made) car, the first model would most likely not resemble something made by Ford or Nissan. There might even be some valid reason to put something that looks like a Prius engine in to a flatbed truck. But we’ve got to start somewhere and Purism has made very reasonable engineering choices, given the available hardware and the stated goals of the project.

From an engineering perspective, if the reception/transmission range of the phone is limited to some degree, that is more of something to expect Purism to fix in a future release, especially if the limitations are the result of limitations of the modem which Purism only purchases and can’t actually fix it themselves. The same goes for any heat-related issues that are outside of Purism’s control for the same reasons. But the need for heat pipes does worry me. When low power is a primary goal, the idea should be to avoid generating heat, not simply to properly vent it. But maybe there is no choice for now with this, given the current state of this model.

Purism needs to make inroads on all fronts. Maybe the Librem 5 will be the cause of some IC manufacturers to take Purism more seriously when it comes to Purism’s next phone model. They need to believe that millions of their chips will sell in to these open sourced smart phones, while weighing how to deal with Purism’s expectations of ‘no firmware blobs’. Maybe an IC manufacturer will develop something that is ideally suited to match Purism’s market. But they need to see a market first. Someone has to start selling open sourced phones first, before chip manufacturers decide to build products that are optimized to sell in to that market. It’s the question of: what comes first, the chicken or the egg? So Purism puts a stake in the ground and says something like ‘we start right here and now’. They’ve got a lot of catching up to do to equal Samsung. But you’ve got to start somewhere.

It is my opinion that anyone who expects the Librem 5 to equal a Samsumg phone plus respecting your privacy and control over your own phone, will be greatly disappointed. I would love to be proven wrong about this. I think that we can expect some kind of a smart phone that fully respects our privacy, with room for technical improvements. That is worth more than seven hundred dollars to me as a first effort.


Yes you are right. I didn’t want to imply that. Just bad wording from me. I meant that purism is working with the interface of the blob contained on the m.2 module. Which is what the fsf counts as equal to a hardware API when it is not updateable (as far as i understood).

So i think the meaning is purism is working with the interface of the m.2 module, which was described by the editor as work on the firmware and lead to confusion.

Otherwise my impressions is the same as @tommes. Firmeware work with WiFI modules i heard of but not for modem modules. That seamed to me more like that they found a chip, the gemalto ones, they liked, but it was only available as bga or mPCIe so they needed to get it on a m.2 module. Which is a custom job but probably done without or very small need for firmware changes. But i might be totaly wrong here.


This brings even more hope for IoT m.2 modem optimisations for mobile use, since it’s been already installed in these tablets. I know that these tablets gonna have a limited space use (at one location - not searching for towers often) compared to cell phones, but at least there isalready some work done at least for power consumption if not both

Though, it’s not shipping with L5 and probably won’t be an option.
At least we can ask -
@nicole.faerber @todd-weaver @joao.azevedo @mladen,
Is Quectel EM06 m.2 modem in consideration at all, by the time evergreen batch is rolling out?


Within Quectel_EM06_Hardware_Design_V1.0. is noted: “EM06 series module (EM06-E/EM06-J/EM06-A*/EM06-LA*) contains Telematics version and Data-only version. Telematics version supports voice and data functions, while Data-only version only supports data function. “*” means under development.”

u/parakeetfour wrote:

Otherwise, a laptop on a WiFi connection with VoIP (and a VPN) will be objectively more useful.


Or a Purism Librem 5 without SIM card. It is still smaller than most laptop computers. That’s my use case, btw. In my country, anonymous SIM cards are practically outlawed, therefore I have no interest in having one. I will just not use the Librem 5 modem.

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Thank you @tommes for pointing out that Purism is using Qualcomm tech and isn’t doing firmware development. I used some of your points in posting a rebuttal on r/linux, but it seems to have been ignored.

In case anyone needs further proof that the BroadMobi BM818 is based on a Qualcomm cellular baseband, see this post by Angus Ainslie:

Here is the link to the press release about the Gemalto PLS8 which says that it uses a Qualcomm cellular baseband:


In that case you might see whether Purism will supply without a modem (unlikely for an agreed price for backer or preorder, but maybe in the future) and/or you should remove the modem once the phone arrives.

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I believe I read somewhere that optionally you could choose between a SIM and a micro SD or 2 micro SD if you didn’t want / need the SIM

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You did but I think it was just someone’s future fantasy, not functionality available now. Maybe this: Primary drive: Dual SD cards in RAID 0

So you can take the modem out but you can’t realistically use that M.2 slot for anything else. (That’s not the SIM slot though, which is different but related.)

You can take out the M.2 card that holds the cellular modem, and put in something else, but that M.2 slot is probably only wired for USB (not PCIe), and it also might involve changing some code in the kernel to allow it. This is a question for the Purism engineers to answer.


No, that’s a different idea to what was in my head… I vaguely feel like it was maybe something Todd said in one of TLG’s videos… I’m skimming them now to try and find it shrug if I was wrong, thank you kieren and amosbatto for clearing up the complexities for me

edit: just re-watched the video and he didn’t mention it where I thought he did, so I now have no idea where the idea got into my head :stuck_out_tongue:


@tommes, here are two links to information about MDM9607.LE.2.2 modem firmware that IMO are worth of mentioning (as you already pointed out):

And IZat is probably there as part of Qualcomm® Trusted Execution Environment.

Just need to wait some news from Purism about these issues. I think it’s really too complex for us.
If there are some issues some people can probably help them. This planet is big and some smart people help other for create an open source world and increase privacy :wink: