Tips-&-Tricks.md

@@ -212,7 +212,10 @@ To get modem information:
 
 * Using the command: `mmcli -m any` will display information on all modems installed on the device, in the case of the Librem 5, there is only one.
 
-But you can also search by modem number, to do that:
+Likewise to get SIM information, you can use the command: `mmcli -i any`
+That will show you your IMSI, among other pieces of information.
+
+But you can also search explicitly to get modem indexes and SIM indexes.
 
 * Firstly, `mmcli -L`
 to list the modems. For example, gives: /org/freedesktop/ModemManager1/Modem/**1**
@@ -222,9 +225,64 @@ to list the modems. For example, gives: /org/freedesktop/ModemManager1/Modem/**1
 * You can also check what mobile network you are on with `mmcli -m M | grep operator`. The operator id comprises three digits for the Mobile Country Code (MCC) followed by two or three digits for the Mobile Network Code (MNC).
 * The output for the SIM index looks like: SIM | dbus path: /org/freedesktop/ModemManager1/SIM/**1** - so the SIM index is 1.
 * Finally, `mmcli -i S` where S is replaced with the SIM index.
-That will show you your IMSI, among other pieces of information.
 * `-i` and `-m` are abbreviated forms of `--sim` and `--modem` respectively.
 
+## Executing an AT command on the modem
+
+There are two ways of doing this.
+
+Method A:
+
+`mmcli` can execute an AT command for you but Modem Manager has to be in "debug" mode for that to work. So:
+
+change the ExecStart line in the file `/lib/systemd/system/ModemManager.service` by adding
+`--debug` so that the line looks like this:
+
+`ExecStart=/usr/sbin/ModemManager --debug`
+
+After that, run the following commands to make the change take effect:
+
+```
+sudo systemctl daemon-reload
+sudo systemctl restart ModemManager.service
+```
+
+Then Modem Manager should be running in debug mode, and you can execute an AT command on the modem e.g.
+
+`sudo mmcli -m any --command=ATI`
+
+The `ATI` command is useful to identify the make and model of modem e.g. what variant of the Broadmobi 818 you have.
+
+This approach has the advantage that if you want to execute the same command more than once, you can repeat the command in the shell.
+
+It is _recommended_ that you take Modem Manager out of debug mode once you have finished i.e. revert the change to the file that you edited above and re-execute the two `systemctl` commands.
+
+Method B:
+
+You can communicate directly with the modem. This involves installing a program like `minicom`, so do that first:
+
+`sudo apt install minicom`
+
+Then `mmcli -m any | grep ttyUSB`
+
+The output will look like:
+```
+ |    ports: cdc-wdm0 (qmi), ttyUSB0 (qcdm), ttyUSB1 (at), ttyUSB2 (at),
+ |           ttyUSB3 (at), wwan0 (net)
+```
+
+Pick any `ttyUSBn` device that is followed by `(at)` e.g. in the above output 1, 2 and 3 are good to use.
+
+`sudo minicom -D /dev/ttyUSBn`
+
+Type Ctrl/A and then E in order to enable local echo.
+
+Type your AT command(s) e.g.
+
+`ATI`
+
+Type Ctrl/A and then X in order to exit from `minicom`.
+
 ## Mobile Country Reference Data
 
 * Reference data for APNs (used to access the internet on the mobile network) is stored in the directory `/usr/share/mobile-broadband-provider-info`