# Fibocom FM350-GL 5G Modem Configuration Guide

Complete reference for configuring the Fibocom FM350-GL modem on Alpine Linux.

## Working Configuration

| Setting | Value |
|---------|-------|
| **Modem** | Fibocom FM350-GL |
| **USB ID** | 0e8d:7126 (Mode 40) |
| **AT Port** | /dev/ttyUSB1 |
| **Network Interface** | eth1 (RNDIS) |
| **APN** | internet (CYTA Cyprus) |

## AT Command Reference

### Sending AT Commands

The FM350-GL doesn't need `stty` configuration. Send commands directly:

```bash
# Pattern for sending AT commands
cat /dev/ttyUSB1 & CAT_PID=$!
sleep 0.3
echo -e 'YOUR_COMMAND\r' > /dev/ttyUSB1
sleep 2
kill $CAT_PID 2>/dev/null
```

### Essential Commands

| Command | Purpose | Example Response |
|---------|---------|------------------|
| `AT` | Test communication | `OK` |
| `AT+CGMI` | Manufacturer | `Fibocom Wireless Inc.` |
| `AT+CGMM` | Model | `FM350-GL` |
| `AT+CSQ` | Signal strength | `+CSQ: 7, 99` (7 = moderate) |
| `AT+CREG?` | Network registration | `+CREG: 0,1` (1 = registered) |
| `AT+CEREG?` | LTE/5G registration | `+CEREG: 0,1` |
| `AT+CCID` | SIM card ID | `+CCID: 893570...` |

### APN Configuration

```bash
# Set APN (CYTA Cyprus uses "internet")
echo -e 'AT+CGDCONT=1,"IP","internet"\r' > /dev/ttyUSB1

# Verify APN is set
echo -e 'AT+CGDCONT?\r' > /dev/ttyUSB1
# Response: +CGDCONT: 1,"IP","internet",""...
```

### Connection Management

```bash
# Activate PDP context (start data connection)
echo -e 'AT+CGACT=1,1\r' > /dev/ttyUSB1
# Response: +CGEV: ME PDN ACT 1, OK

# Get assigned IP address
echo -e 'AT+CGPADDR=1\r' > /dev/ttyUSB1
# Response: +CGPADDR: 1,"10.156.167.104",""

# Get full connection details (DNS, MTU)
echo -e 'AT+CGCONTRDP=1\r' > /dev/ttyUSB1
# Response includes DNS servers
```

### USB Mode Control

```bash
# Check current USB mode
echo -e 'AT+GTUSBMODE?\r' > /dev/ttyUSB1
# Response: +GTUSBMODE: 40

# Available modes
echo -e 'AT+GTUSBMODE=?\r' > /dev/ttyUSB1
# Response: +GTUSBMODE: (40,41)

# Switch modes (requires modem reset)
echo -e 'AT+GTUSBMODE=40\r' > /dev/ttyUSB1

# Reset modem
echo -e 'AT+CFUN=1,1\r' > /dev/ttyUSB1
```

## USB Modes

| Mode | USB Product ID | Description | AT Commands |
|------|----------------|-------------|-------------|
| 40 | 0e8d:7126 | RNDIS mode | ✅ Work on ttyUSB1 |
| 41 | 0e8d:7127 | Extended mode | ❌ Don't work |

**Important:** Stay in Mode 40 for reliable AT command access.

## Network Interface Configuration

### Why DHCP Doesn't Work

The RNDIS interface (`eth1`) does **not** provide DHCP. The modem manages the connection internally. You must:

1. Get the IP from the modem via `AT+CGPADDR=1`
2. Configure the interface manually

### Manual Configuration

```bash
# Get IP from modem (replace with actual value)
MODEM_IP="10.156.167.104"

# Configure interface
ip link set eth1 up
ip addr flush dev eth1
ip addr add $MODEM_IP/32 dev eth1
ip route add default dev eth1 metric 50

# Test
ping -c 3 8.8.8.8
```

## CYTA Cyprus Settings

| Setting | Value |
|---------|-------|
| APN | `internet` |
| DNS Primary | 195.14.130.220 |
| DNS Secondary | 195.14.154.100 |
| Network Name | Vodafone |

## Complete Connection Sequence

```bash
#!/bin/sh
# Full connection sequence for FM350-GL with CYTA SIM

AT_PORT="/dev/ttyUSB1"
APN="internet"

# 1. Configure APN
cat $AT_PORT & PID=$!; sleep 0.3
echo -e "AT+CGDCONT=1,\"IP\",\"$APN\"\r" > $AT_PORT
sleep 2; kill $PID 2>/dev/null

# 2. Activate connection
cat $AT_PORT & PID=$!; sleep 0.3
echo -e "AT+CGACT=1,1\r" > $AT_PORT
sleep 3; kill $PID 2>/dev/null

# 3. Get IP address
MODEM_IP=$(timeout 5 sh -c "
    cat $AT_PORT & PID=\$!
    sleep 0.3
    echo -e 'AT+CGPADDR=1\r' > $AT_PORT
    sleep 2
    kill \$PID 2>/dev/null
" 2>&1 | grep CGPADDR | grep -oE '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+' | head -1)

echo "Modem IP: $MODEM_IP"

# 4. Configure interface
ip link set eth1 up
ip addr flush dev eth1
ip addr add $MODEM_IP/32 dev eth1
ip route add default dev eth1 metric 50

# 5. Test
ping -c 3 8.8.8.8
```

## Troubleshooting

### AT Commands Not Responding

**Symptoms:** No response to AT commands on any port.

**Solutions:**
1. Check modem is in Mode 40: `lsusb | grep 7126`
2. If in Mode 41 (7127), AT commands won't work - need physical access to switch back
3. Try different ports: ttyUSB0, ttyUSB1, ttyUSB2

### ttyUSB3 Shows as Regular File

**Symptoms:** `ls -la /dev/ttyUSB3` shows `-rw-r--r--` instead of `crw-rw----`

**Fix:**
```bash
rm -f /dev/ttyUSB3
mknod /dev/ttyUSB3 c 188 3
chmod 660 /dev/ttyUSB3
chown root:dialout /dev/ttyUSB3
```

### stty Errors

**Symptoms:** `stty: /dev/ttyUSB1: cannot perform all requested operations`

**Solution:** Don't use `stty`. Send AT commands directly with `echo` and `cat`.

### No IP on eth1

**Symptoms:** `ip addr show eth1` shows no inet address after DHCP attempt.

**Solution:** RNDIS doesn't use DHCP. Configure IP manually from `AT+CGPADDR=1`.

### ModemManager Not Detecting Modem

**Note:** ModemManager doesn't work well with this modem in RNDIS mode. Use AT commands directly instead.

### Signal Strength Interpretation

| CSQ Value | dBm | Quality |
|-----------|-----|---------|
| 0 | -113 or less | No signal |
| 1-9 | -111 to -95 | Poor |
| 10-14 | -93 to -85 | Fair |
| 15-19 | -83 to -75 | Good |
| 20-30 | -73 to -53 | Excellent |
| 31 | -51 or better | Excellent |
| 99 | Unknown | - |

## Kernel Modules

These modules should be loaded for MBIM/QMI support (optional):

```bash
modprobe cdc-wdm
modprobe cdc_mbim
modprobe qmi_wwan
modprobe cdc_ncm

# Verify
lsmod | grep -E '(cdc|qmi)'
```

## Files on Device

| Path | Purpose |
|------|---------|
| `/usr/local/bin/connect-5g.sh` | Auto-connection script |
| `/etc/init.d/5g-router` | OpenRC service |
| `/var/log/5g-router.log` | Connection log |
| `/etc/iptables/rules.v4` | Firewall/NAT rules |

## Service Management

```bash
# Check status
service 5g-router status

# Restart connection
service 5g-router restart

# View logs
tail -f /var/log/5g-router.log

# Check if enabled at boot
rc-update show | grep 5g-router
```