Add SIM7600G-H LTE modem setup guide for Rock 5T

i18n/en/docusaurus-plugin-content-docs/current/rock5/rock5t/hardware-design/m2-b-key-sim7600g-h.md

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+---
+sidebar_position: 10
+---
+
+# M.2 B Key - SIM7600G-H LTE Setup
+
+**System:** Radxa Rock 5T · Ubuntu 24.04 · Kernel 6.1.115-3-rockchip  
+**Modem:** SimCom SIM7600G-H in M.2 B-Key slot  
+**Goal:** Automatic LTE connection on every boot
+
+---
+
+## 1. Identify GPIO Pins
+
+The SIM7600G-H is controlled via 4 GPIO pins of the RK3588.  
+The Linux GPIO number is calculated as: `Bank × 32 + Group × 8 + Bit`
+
+| Signal | GPIO Name | Calculation | Linux No. | Logic |
+|---|---|---|---|---|
+| `4G_PWREN` | GPIO2_B1 | 2×32 + 1×8 + 1 | **73** | Active-HIGH |
+| `4G_WAKE_ON_HOST` | GPIO2_B2 | 2×32 + 1×8 + 2 | **74** | Active-HIGH |
+| `4G_RESET#` | GPIO2_B3 | 2×32 + 1×8 + 3 | **75** | Active-LOW |
+| `4G_DISABLE#` | GPIO3_A6 | 3×32 + 0×8 + 6 | **102** | Active-LOW |
+
+:::caution
+`RESET#` and `W_DISABLE#` are Active-Low signals. A LOW level means reset active or RF disabled respectively. Setting these pins LOW will prevent the modem from starting.
+:::
+
+---
+
+## 2. Export GPIOs and Start Modem (Manual Test)
+
+```bash
+# Export GPIOs and set as output
+for pin in 73 74 75 102; do
+    echo $pin | sudo tee /sys/class/gpio/export
+    echo out | sudo tee /sys/class/gpio/gpio${pin}/direction
+done
+
+# Set clean initial state
+echo 0 | sudo tee /sys/class/gpio/gpio73/value   # Power OFF
+echo 1 | sudo tee /sys/class/gpio/gpio75/value   # RESET# HIGH (inactive)
+echo 1 | sudo tee /sys/class/gpio/gpio102/value  # W_DISABLE# HIGH (RF enabled)
+sleep 1
+
+# Power on
+echo 1 | sudo tee /sys/class/gpio/gpio73/value
+sleep 2
+
+# Send reset pulse
+echo 0 | sudo tee /sys/class/gpio/gpio75/value
+sleep 0.5
+echo 1 | sudo tee /sys/class/gpio/gpio75/value
+sleep 15
+
+# Modem should now appear
+lsusb | grep -i sim
+# Expected: ID 1e0e:9001 SimTech, Incorporated
+```
+
+---
+
+## 3. Verify Modem
+
+```bash
+mmcli -L
+mmcli -m 0
+```
+
+Expected output shows:
+- `model: SIMCOM_SIM7600G-H`
+- `state: locked` (SIM PIN required)
+- `ports: cdc-wdm0 (qmi), ttyUSB0..4, wwan0 (net)`
+
+---
+
+## 4. Unlock SIM PIN and Disable PIN Lock
+
+```bash
+# Install minicom
+sudo apt install minicom -y
+
+# Connect to AT command port
+sudo minicom -D /dev/ttyUSB2 -b 115200
+```
+
+In minicom, run the following AT commands:
+
+```
+AT+CPIN?           # → +CPIN: SIM PIN  (PIN required)
+AT+CPIN="1234"     # Enter your PIN
+AT+CPIN?           # → +CPIN: READY
+
+# Disable PIN lock permanently (recommended for embedded use)
+AT+CLCK="SC",0,"1234"
+
+# Check network
+AT+CSQ             # Signal strength (>10 = good)
+AT+CREG?           # → 0,1 = registered
+AT+COPS?           # Show network operator
+```
+
+---
+
+## 5. Solve APN Issue (Telekom Carrier Config)
+
+The modem ships with `carrier config: Commercial-DT`. The Deutsche Telekom network enforces `INTERNET.TELEKOM` as the only allowed APN. MVNOs running on the Telekom network (e.g. Congstar, Aldi Talk) must also use this APN.
+
+```bash
+# Install libqmi
+sudo apt install libqmi-utils -y
+
+# Set interface to raw_ip mode
+sudo ip link set wwan0 down
+echo 'Y' | sudo tee /sys/class/net/wwan0/qmi/raw_ip
+sudo ip link set wwan0 up
+
+# Create qmi-network configuration
+sudo nano /etc/qmi-network.conf
+```
+
+```
+APN=INTERNET.TELEKOM
+PROFILE=2
+```
+
+```bash
+# Test connection
+sudo qmi-network /dev/cdc-wdm0 start
+# → "Network started successfully"
+
+# Read IP from QMI
+sudo qmicli -d /dev/cdc-wdm0 --wds-get-current-settings
+```
+
+---
+
+## 6. Automatic Boot Script
+
+Create the connection script:
+
+```bash
+sudo nano /usr/local/bin/sim7600-connect.sh
+```
+
+```bash
+#!/bin/bash
+
+# GPIO Init — Power on modem
+for pin in 73 74 75 102; do
+    echo $pin > /sys/class/gpio/export 2>/dev/null
+    echo out > /sys/class/gpio/gpio${pin}/direction
+done
+echo 0 > /sys/class/gpio/gpio73/value   # Power off
+echo 1 > /sys/class/gpio/gpio75/value   # RESET# inactive
+echo 1 > /sys/class/gpio/gpio102/value  # RF enabled
+sleep 1
+echo 1 > /sys/class/gpio/gpio73/value   # Power on
+sleep 2
+echo 0 > /sys/class/gpio/gpio75/value   # Reset pulse
+sleep 0.5
+echo 1 > /sys/class/gpio/gpio75/value
+
+# Wait for USB modem to appear (max 30s)
+echo "Waiting for modem..."
+for i in $(seq 1 30); do
+    [ -c /dev/cdc-wdm0 ] && break
+    sleep 1
+done
+
+# Clean up old QMI state (prevents "PDH already exists" error)
+rm -f /tmp/qmi-network-state-cdc-wdm0
+
+# Prepare interface
+ip link set wwan0 down
+echo 'Y' > /sys/class/net/wwan0/qmi/raw_ip
+ip link set wwan0 up
+
+# Bring up connection
+qmi-network /dev/cdc-wdm0 stop 2>/dev/null
+sleep 1
+qmi-network /dev/cdc-wdm0 start
+sleep 3
+
+# Get IP address from QMI and configure interface
+IP=$(qmicli -d /dev/cdc-wdm0 --wds-get-current-settings 2>&1 \
+    | grep "IPv4 address" | awk '{print $NF}')
+DNS1=$(qmicli -d /dev/cdc-wdm0 --wds-get-current-settings 2>&1 \
+    | grep "IPv4 primary DNS" | awk '{print $NF}')
+DNS2=$(qmicli -d /dev/cdc-wdm0 --wds-get-current-settings 2>&1 \
+    | grep "IPv4 secondary DNS" | awk '{print $NF}')
+
+if [ -n "$IP" ]; then
+    ip addr flush dev wwan0
+    ip addr add ${IP}/32 dev wwan0
+    # No gateway needed for raw_ip point-to-point
+    ip route add default dev wwan0 metric 700
+    resolvectl dns wwan0 $DNS1 $DNS2 2>/dev/null
+    echo "LTE active: $IP"
+else
+    echo "ERROR: Failed to get IP address!"
+    exit 1
+fi
+```
+
+```bash
+sudo chmod +x /usr/local/bin/sim7600-connect.sh
+```
+
+---
+
+## 7. Create Systemd Service
+
+```bash
+sudo nano /etc/systemd/system/sim7600-init.service
+```
+
+```ini
+[Unit]
+Description=SIM7600 Modem Init and Connect
+After=sysinit.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/local/bin/sim7600-connect.sh
+
+[Install]
+WantedBy=multi-user.target
+```
+
+```bash
+sudo systemctl daemon-reload
+sudo systemctl enable sim7600-init.service
+
+# Disable ModemManager (conflicts with direct QMI usage)
+sudo systemctl disable ModemManager
+```
+
+---
+
+## 8. Toggle LTE Manually
+
+Create a script to turn LTE off when using WiFi:
+
+```bash
+sudo nano /usr/local/bin/lte-off.sh
+```
+
+```bash
+#!/bin/bash
+qmi-network /dev/cdc-wdm0 stop
+rm -f /tmp/qmi-network-state-cdc-wdm0
+ip addr flush dev wwan0
+ip link set wwan0 down
+echo 0 > /sys/class/gpio/gpio73/value
+echo "LTE off."
+```
+
+```bash
+sudo chmod +x /usr/local/bin/lte-off.sh
+
+# Usage:
+sudo lte-off.sh              # Turn LTE off, use WiFi
+sudo sim7600-connect.sh      # Turn LTE back on
+```
+
+---
+
+## 9. Test Connection
+
+```bash
+# After reboot or manual start:
+ip addr show wwan0          # IPv4 address must be visible
+ip route show               # default via wwan0 must be present
+ping -c 3 8.8.8.8           # Ping over LTE
+curl -s ifconfig.me         # Show public IP
+nmcli radio wifi off        # Disable WiFi — LTE only
+ping -c 3 google.com        # DNS test
+nmcli radio wifi on         # Re-enable WiFi
+```
+
+---
+
+## Troubleshooting
+
+| Problem | Cause | Solution |
+|---|---|---|
+| Modem not visible in `lsusb` | RESET# logic inverted (Active-Low!) | Keep gpio75 = HIGH during normal operation |
+| `unknown-apn` error | Telekom carrier config blocks custom APNs | Use `APN=INTERNET.TELEKOM` |
+| `PDH already exists` error | Stale state file in /tmp | `rm -f /tmp/qmi-network-state-cdc-wdm0` |
+| No IPv4 after connect | DHCP does not work in raw_ip mode | Set IP manually via `qmicli --wds-get-current-settings` |
+| Service fails at boot | ModemManager blocks cdc-wdm0 | Disable ModemManager via systemctl |