SIM7600G-H 4G Modem User Guide

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

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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.

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Export GPIOs and Start Modem (Manual Test)

# 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

---

Verify Modem

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)

---

Unlock SIM PIN and Disable PIN Lock

# 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

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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.

# 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

# 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

---

Automatic Boot Script

Create the connection script:

sudo nano /usr/local/bin/sim7600-connect.sh

#!/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

sudo chmod +x /usr/local/bin/sim7600-connect.sh

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Create Systemd Service

sudo nano /etc/systemd/system/sim7600-init.service

[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

sudo systemctl daemon-reload
sudo systemctl enable sim7600-init.service

# Disable ModemManager (conflicts with direct QMI usage)
sudo systemctl disable ModemManager

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Toggle LTE Manually

Create a script to turn LTE off when using WiFi:

sudo nano /usr/local/bin/lte-off.sh

#!/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."

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

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Test Connection

# 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

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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