Mikrotik wAP R (RBwAPR-2nD) SIM card support

I'm looking into a device with LTE support and ran across the Mikrotik wAP R. A very similar device is already supported, and the miniPCIe LTE card I have claims to have linux support via a standard driver.

What I'm wondering about is how the SIM card slot on this device works and how it interfaces with the LTE card. If it's even supported, how do you use it to authenticate a wireless connection? What interface is it? How does it show up to the OS?

Hm,I think it is connected to LTE card via traces

Looks like you're right. According to Wikipedia, part of the electrical interface for mini PCIe:

SIM card for GSM and WCDMA applications (UIM signals on spec.).

And reading the technical docs for my wireless card (a Sierra Wireless AirPrime MC73xx),

The module supports one SIM (Subscriber Identity Module) (1.8 V or 3 V)...The SIM pins provide the connections necessary to interface to a SIM socket located on the host device. Voltage levels over this interface comply with 3GPP standards.

In case anyone's curious, here's the MiniPCIe/SIM pinout:

Name Pin Description SIM contact number Notes
USIM_PWR 8 SIM voltage 1 Power supply for SIM
USIM_DATA 10 Data I/O 7 Bi-directional SIM data line
USIM_CLK 12 Serial clock 3 Serial clock for SIM data
USIM_RST 14 Reset 2 Active low SIM reset
USIM_GND Ground 5 USIM_GND is common to module ground

TL;DR: Motherboards supporting LTE cards wire SIM card pins directly to the LTE card over Mini PCIe reserved for a SIM card connection.
In order to use these cards, your motherboard needs a SIM connector, or you need to wire it up some other way. This probably explains LTE cards I saw for sale that said "For Dell only;" they must have used non-standard pins.

So then SIM slot is a non-worry but PCI needs to be enabled and most likely some GPIO compared to standard wAP.

I can take a look at GPL patch I got couple of days ago,If this board is even there

AFAIK, the Sierra Wireless cards with Dell branding have some non-standard firmware in them. I've been advised that re-flashing them can be a pain. Based on that, I chose to purchase a new Sierra Wireless module from an authorized component supplier.

The only "gotcha" might be if there is a SIM switch that needs a GPIO level to either enable the SIM connection, or to switch between two (such as on the PCEngines dual-SIM boards).

Edit: The OpenWRT support for wireless cards is reasonably good. QMI would be the first I would try. (Linux_QMI_SDK_04_00_13_Customer_Release_Note_Rev2_0.pdf confirms that the EM/MC73xx support QMI) https://openwrt.org/docs/guide-user/network/wan/wwan/ltedongle is a good starting point.

Exactly,that is what I mentioned.
Altough since this only has one PCIE slot and it is primary for LTE it possibly could not require anything special.
I looked into GPL but there are only wAP,wAPG and wAP LTE.
What names do you find in Resources and Routerboard windows in Winbox?

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wAP R and RBwAPR-2nD, respectively.