Raspberry Pi GPRS/GPS notes
===

I'm focusing on a SIM4320(A) chip:

* [Adafruit](https://www.adafruit.com/product/2687)
  - [simcom](https://cdn-shop.adafruit.com/datasheets/SIMCOM_SIM5320_ATC_EN_V2.02.pdf)
  - [sim4320 datasheet](https://www.tinyosshop.com/datasheet/SIM5320_Hardware+Design_V1.07.pdf)
* [DIYmall](https://www.amazon.com/gp/product/B06Y3N1BD6)
* [Arduino SIM5320A](https://www.amazon.com/gp/product/B01HNV3ZXC)

GPRS
---

| Raspberry Pi Pin | FONA Pin |
|---|---|
| 3.3v (1) | Vio (4) |
| GND (6) | GND (3) |
| TXD (8) | RX (6) |
| RXD (10) | TX (7) |

On the Raspberry Pi (RPi 3B+, Raspbian 2019-07-10 Buster)

```
sudo bash
apt-get update
apt-get install ppp screen minicom

# disable rpi serial interface so we can use it from FONA
#
echo 'enable_uart=1' >> /boot/config.txt

# setup ppp configuration
#
cat > /etc/ppp/peers/fona <<EOF
connect "/usr/sbin/chat -v -f /etc/chatscripts/gprs"
/dev/serial0
115200
noipdefault
usepeerdns
defaultroute
persist
noauth
nocrtscts
local
EOF
shutdown -r now
```

At this point, after reboot, I tested to make sure the serial connection was at least responding to `AT` commands:

```
sudo bash
minicom -c on -D /dev/serial0
AT
```

* The `AT` command should show up because the FONA should echo the commands
* The FONA should respond with `OK`

I **think** I only had to add the `enable_uart=1` in the `/boot/config.txt` and wire the serial connection
for this to work...

---

To setup a `ppp` connection, issuing:

```
pon fona
```

as root should work.

If there are troubles, look at `dmesg` and `/var/log/syslog` for clues as to what went wrong.

---

* After setup, I'm having trouble with `wwan0`. Doing `ifconfig wwan0 down` and then resetting the `ppp` connection
  (`poff fona ; pon fona`), I get internet connectivity.
* I have to physically hold down the 'on' button for 5s to turn on the GPRS and GPS functionality

GPS
---

I'm using an active antennae.

I've soldered the 'bias' bin on the 3G Fona module.

Note that I couldn't find any reference on Adafruit's site about soldering the 'bias' bridge.
I only found this information when looking at other users problems ([src](https://forum.core-electronics.com.au/t/adafruit-fona-gps-not-working/644/8)).
It turns out Adafruit does mention it in one of their PDF guides ([src](https://cdn-learn.adafruit.com/downloads/pdf/adafruit-fona-3g-cellular-gps-breakout.pdf)).

There is a USB connection to the FONA which is how, I believe, the `ttyUSB` interfaces are coming up.
The USB to serial connection can be used for the GPS information whereas the direct serial connection
is used for the GPRS modem.

* I was not getting a fix on the satellites until I soldered the 'bias' bridge on the FONA.
* I had to reseat the small GPS antennae connector
* Connect to serial interface via `/dev/ttyUSB3`
  - Note that `/dev/ttyUSB2` looks to be another viable candidate but maybe what goes on in `/dev/ttyUSB3` is mirrored
    in `/dev/ttyUSB2`
  - `/dev/ttyUSB0` and `/dev/ttyUSB1` show up when the FONA is powered on but I haven't been able to get any response
    when connecting via `minicom` to either of those interfaces
  - to connect from the command line `minicom -c on -D /dev/ttyUSB2` (8N1 115200, hardware flow control off)
* Turn on the GPS functionality by issuing `AT+CGPS=1`
* To poll every 3 seconds with full NMEA message output, issue `AT+CGPSINFOCFG=3,31`
  - Look for the `$GPRMC,...` line as that has the easiest to read lat/lon positions

See [NMEA sentence information](http://aprs.gids.nl/nmea/) and 

References
---

* [Initial State tutorial](https://github.com/initialstate/fona-raspberry-pi-3/wiki)
* [Adafruit FONA tethering tutorial](https://learn.adafruit.com/fona-tethering-to-raspberry-pi-or-beaglebone-black/overview)
* [Adafruit FONA 3G tutorial](https://learn.adafruit.com/adafruit-fona-3g-cellular-gps-breakout/overview)
* [Disabling serial port](https://www.cube-controls.com/2015/11/02/disable-serial-port-terminal-output-on-raspbian/)
* [Disable WiFi and Bluetooth](https://blog.sleeplessbeastie.eu/2018/12/31/how-to-disable-onboard-wifi-and-bluetooth-on-raspberry-pi-3/)
* [SO: How do I make serial work on ...](https://raspberrypi.stackexchange.com/questions/45570/how-do-i-make-serial-work-on-the-raspberry-pi3-pi3b-pizerow)
* [GPS - NMEA sentence information](http://aprs.gids.nl/nmea/)
* [NMEA-0183 messages: Overview](https://www.trimble.com/OEM_ReceiverHelp/V4.44/en/NMEA-0183messages_MessageOverview.html)
* [Adafruit picture of FONA (see soldered bridge with active antenaae)](https://cdn-learn.adafruit.com/assets/assets/000/027/349/original/adafruit_products_Fona_America_top_demo_ORIG.jpg?1440189319)
* [GH: Adafruit FONA Simcom 3G Breakout PCB](https://github.com/adafruit/Adafruit-FONA-SIMCOM-3G-Breakout-PCB)
* [Simcom SIM5320 AT command set](https://cdn-shop.adafruit.com/datasheets/SIMCOM_SIM5320_ATC_EN_V2.02.pdf)