K3 Swapping the 3G modem for a 4G modem

[wishindo]

With the sunset of 3G in the USA in 4ish months as-of posting, I was thinking about my Kindle Keyboard that has 3G. Surely I could just replace the modem with a 4G capable one, and have the Kindle continue to function as-intended^1 by Amazon, theoretically.

To do so, I would have to find a modem that meets the following specifications:

• 4G-capable
• Mini-PCIe full-length form-factor^2
• USB/UART connectivity^3
• Usable with only 1 antenna

Drivers could be a problem though, I don't know how Linux handles cellular modems - whether it's one universal driver per interface or if they're device specific.

Anyone have any input?

^1 - When I say as-intended, I mean as a stock unit works currently in terms of downloading books and browsing Amazon and Wikipedia.
^2 - A half-length card in an adapter could work, but would need an antenna extension cable.
^3 - Spec pulled from page 11 of the DTP-600W datasheet. I don't know which interface is used by the kindle, but a modem supporting both shouldn't be a problem, interface-wise at least.

[wishindo]

After sleeping on this, I've realized a critical flaw in my thinking - who says Amazon will keep paying for the current SIM after 3G is shutdown? So I'll probably need to do a SIM swap as well.

Also, I've come up with an alternative scheme - replace the 3G modem with a USB flash drive for extra storage (4GB is tiny nowadays) using a mini-PCIe to USB 2.0 adapter/riser like in this picture. Though how exactly would it be mounted in the filesystem is unknown to me currently.

[wishindo]

So I looked into the device a bit, saw it had an fstab file. For extra storage, would it be as simple as modifying fstab to mount the extra storage in /mnt/us/documents? I figured there'd be more hoops to go through, what with USB Mass Storage mode of the Kindle... Hope I'm not jinxing it though.

Granted, I don't have any storage hardware right now to test with, but it is on order and set to arrive by Oct 18 (2021-10-18). When it arrives and I've had time to experiment with it, I'll make a new thread. This thread will be for modem swapping.

Modem swapping may happen Soon™ after Halloween (2021-10-31) as I don't want to sink too much of one paycheck into these shenanigans.

[Quoth]

You'd need a lot of software changes to support any change, even if replacement HW is compatible. A newer Kobo or Kindle with WiFi and a phone as a WiFi hotspot if you have no broadband is a simple 100% working solution.

The existing SIM may or may not work with Amazon's 4G suppliers and they could end the service or terminate your SIM anyway. The service only gives very limited Internet access here. Little was ever free (Amazon Shop & Wikipedia) and also expiring certs are an HTTPS issue.

I have a 3G only DXG, and though in Ireland there is no date at all for ending 3G, and 2G (GSM) may still work (Smart meters and burglar alarms use 2G and 3G), the DXG is essentially junk. The Wifi based KK3 is a little better as it will render KF8 ebooks. The 2.5.8 and DX, KK2 and DXG only do very basic KF7 ebooks.

[katadelos]

Cool project!

Originally Posted by wishindo

Drivers could be a problem though, I don't know how Linux handles cellular modems - whether it's one universal driver per interface or if they're device specific.

I've noticed that many USB/PCI-e 3G modules use the "option" kernel module (which tends to be included on both 3G/WiFi only Kindle variants. No idea about 4G modules but you might struggle to find one which has a kernel module available for the ancient kernel version used on the K3.

Originally Posted by wishindo

Also, I've come up with an alternative scheme - replace the 3G modem with a USB flash drive for extra storage (4GB is tiny nowadays) using a mini-PCIe to USB 2.0 adapter/riser like in this picture. Though how exactly would it be mounted in the filesystem is unknown to me currently.

This could present a problems - looks like the USB port on that card is surface mounted so you probably won't be able to replace the back of the case of the Kindle without cutting a hole? Using a Mini-PCIe to SD adapter might be a better option. The hardware should be detected automatically and you should be able manually mount it over SSH if it's ext3 formatted (Kindles lack support for ext4 and quite a few ext3 features).

Shouldn't be massively difficult to adapt the upstart userstore scripts to present the storage over USB mass storage mode assuming that things work in the first place -this wiki page is a good overview of the method used to achieve this on pre-PW4 Kindles.

Originally Posted by Quoth

... and also expiring certs are an HTTPS issue.

It's likely that this issue could be worked around by extracting the cert bundle and/or keystore from a more recent device and transplanting it to the older device - I've not got round to trying this on one of my older Kindles yet though.

[erikhoudini]

Would probably be more feasible to use a Pi Zero and rework the button and screen than it would be to reverse engineer the software to accept a new sim