make a serviceDefn for wwan

modules/cdc-ncm/wwan.nix

@@ -0,0 +1,47 @@
+{
+  liminix
+, usb-modeswitch
+, ppp
+, lib
+, svc
+}:
+{ apn, username, password, authType }:
+let
+  inherit (liminix.services) oneshot;
+  authTypeNum = if authType == "pap" then "1" else "2";
+  chat = lib.escapeShellArgs [
+    # Your usb modem thing might present as a tty that you run PPP
+    # over, or as a network device ("ndis" or "ncm"). The latter
+    # kind is to be preferred, at least in principle, because it's
+    # faster.  This initialization sequence works for the Huawei
+    # E3372, and took much swearing: the error messages are *awful*
+    "" "AT"
+    "OK" "ATZ"
+    # create PDP context
+    "OK" "AT+CGDCONT=1,\"IP\",\"${apn}\""
+    # activate PDP context
+    "OK"  "AT+CGACT=1,1"
+    # setup username and password per requirements of sim provider.
+    # (caret is special to chat, so needs escaping in AT commands)
+    "OK"  "AT\\^AUTHDATA=1,${authTypeNum},\"\",\"${password}\",\"${username}\""
+    # start the thing (I am choosing to read this as "NDIS DialUP")
+    "OK" "AT\\^NDISDUP=1,1"
+  ];
+  modemConfig = oneshot {
+    name = "modem-configure";
+    # this is currently only going to work if there is one
+    # modem only plugged in, it is plugged in already at boot,
+    # and nothing else is providing a USB tty.
+    # https://stackoverflow.com/questions/5477882/how-to-i-detect-whether-a-tty-belonging-to-a-gsm-3g-modem-is-a-data-or-control-p
+    up = ''
+      sleep 2
+      ${usb-modeswitch}/bin/usb_modeswitch -v 12d1 -p 14fe --huawei-new-mode
+      sleep 5
+      ${ppp}/bin/chat -s -v ${chat}  0<>/dev/ttyUSB0 1>&0
+    '';
+    down = "chat -v '' ATZ OK  </dev/ttyUSB0 >&0";
+  };
+in svc.network.link.build {
+  ifname = "wwan0";
+  dependencies = [ modemConfig ];
+}