Use cellular modems with VintageNet

This module is not intended to be called directly but via calls to VintageNet. Here's a typical example:

VintageNet.configure(
  "ppp0",
  %{
    type: VintageNetMobile,
    vintage_net_mobile: %{
      modem: VintageNetMobile.Modem.QuectelBG96,
      service_providers: [%{apn: "super"}]
    }
  }
)

The :modem key should be set to your modem implementation. Cellular modems tend to be very similar. If vintage_net_mobile doesn't support your modem, see the customizing section. It may just be a copy/paste away. See your modem module for modem-specific options. The following keys are supported by all modems:

• :service_providers - This is a list of service provider information
• :chatscript_additions - This is a string (technically iodata) for custom modem initialization.

The :service_providers key should be set to information provided by each of your service providers. It is common that this is a list of one item. Circumstances may require you to list more than one, though. Additionally, modem implementations may require more or less information depending on their implementation. (It's possible to hard-code the service provider in the modem implementation. In that case, this key isn't used and should be set to an empty list. This is useful when your cellular modem provides instructions that magically work and the AT commands that they give are confusing.)

Information for each service provider is a map with some or all of the following fields:

• :apn (required) - e.g., "access_point_name"
• :usage (optional) - :eps_bearer (LTE) or :pdp (UMTS/GPRS)

Your service provider should provide you with the information that you need to connect. Often it is just an APN. The Gnome project provides a database of service provider information that may also be useful.

Here's an example with a service provider list:

  %{
    type: VintageNetMobile,
    modem: your_modem,
    vintage_net_mobile: %{
      service_providers: [
        %{apn: "wireless.twilio.com"}
      ],
      chatscript_additions: "OK AT"
    }
  }

Custom modems

VintageNetMobile allows you add custom modem implementations if the built-in ones don't work for you. See the VintageNetMobile.Modem behaviour.

In order to implement a modem, you will need:

1. Instructions for connecting to the modem via your Linux. Sometimes this involves usb_modeswitch or knowing which serial ports the modem exposes.
2. Example chat scripts. These are lists of AT commands and their expected responses for configuring the service provider and entering PPP mode.
3. (Optional) Instructions for checking the signal strength when connected.

One strategy is to see if there's an existing modem that looks similar to yours and modify it.