SIM7080G Pico Library

A C++17 library for the Raspberry Pi Pico that drives a SIMCom SIM7080G LTE Cat-M / NB-IoT modem over UART via AT commands.

Built from a real GPS/LTE car-tracker project. The library covers the full connectivity lifecycle: modem startup, network attachment, PDP context activation, MQTT publish/subscribe, and TLS certificate upload to modem flash.

Features

Interrupt-driven UART receive buffer with unsolicited result code (URC) dispatch
AT command helper that waits for final results (OK, ERROR, +CME, +CMS) instead of returning on partial response substrings
Prompt/payload command helper for MQTT, HTTP body upload, SMS, TCP sends and modem file uploads
Basic modem identity commands (ATI, CGMI, CGMM, CGMR, CGSN, GCAP)
SIM identity/status helpers (CPIN, CIMI, CCID, optional PIN unlock)
LTE Cat-M / NB-IoT mode selection and full network attachment sequence (SIM PIN check, signal quality, GPRS attachment polling, APN, PDP context)
3GPP PDP helpers (CGATT, CGDCONT, CGACT, CGPADDR, CGAUTH)
App Network helpers (CNCFG, CNACT, typed CNACT? state)
MQTT configure, connect (with retry), publish, subscribe, unsubscribe, state and disconnect
HTTP(S) command wrappers (SHCONF, SHSSL, SHCONN, SHBOD, SHREQ, length-based SHREAD)
TLS file upload and SSL context configuration (CFS*, CSSLCFG)
GNSS power/start/info parsing and wait-for-fix helper (CGNS*)
SMS text-mode send/list/read/delete helpers
Thin TCP/UDP wrappers for the CA* command family
Power, reboot, slow-clock, PSM and eDRX wrappers
Battery status reading (charge state, level %, voltage)
Comprehensive AT+CPSI? response parser — handles GSM and LTE variants, missing fields represented via std::optional
Modular CMake build: three static libraries (at_commands → sim7080g → app)

Hardware

Pin Defaults

Signal	GPIO	Note
Modem UART TX	GP0	Pico → modem RXD
Modem UART RX	GP1	Modem TXD → Pico
Modem power key	GP14	2.5 s active-high pulse to boot module
Debug stdio TX	GP4	UART1 — connect to your debug probe/USB
Debug stdio RX	GP5	UART1
LED	GP25	Onboard Pico LED

All modem pins are configurable through SIM7080GConfig before calling sim7080g_init(config).

Wiring

Pico                    SIM7080G breakout
────────────────        ──────────────────
GP0  (UART0 TX) ──────► RXD
GP1  (UART0 RX) ◄────── TXD
GP14 (GPIO OUT) ──────► PWRKEY
3V3             ──────► VCC    (verify your breakout — some require 4.2 V / 5 V)
GND             ──────  GND

Dependencies

Dependency	Version	How
Raspberry Pi Pico SDK	≥ 2.1.0	Set `PICO_SDK_PATH` or use the VS Code extension
nlohmann/json	3.x	Single-header bundled in `json/json.hpp`

Build

git clone https://github.com/BRobin55/sim7080g_showcase
cd sim7080g_showcase

cmake -S . -B build -DPICO_BOARD=pico
cmake --build build --parallel

Flash build/sim7080g_showcase.uf2 to your Pico (hold BOOTSEL while connecting USB).

If the Pico SDK is not on PATH, pass -DPICO_SDK_PATH=/path/to/pico-sdk to the first cmake command or set the environment variable PICO_SDK_PATH.

Repository Layout

sim7080g_showcase/
├── sim7080g/                   # Modem library  (libsim7080g.a)
│   ├── SIM7080G.h/.cpp         #   UART init, IRQ buffer, URC dispatch
│   ├── AT.h/.cpp               #   AT command send/receive with timeout
│   ├── Network.h/.cpp          #   High-level network lifecycle
│   ├── MQTT.h/.cpp             #   MQTT helpers (config, connect, pub, sub)
│   ├── FileSystem.h/.cpp       #   TLS credential file upload
│   └── at_commands/            # Low-level AT wrappers  (libat_commands.a)
│       ├── basic.h/.cpp        #   AT / ATE / ATI / CGMI / CGSN / GCAP
│       ├── battery.h/.cpp      #   AT+CBC  — battery status
│       ├── file_system.h/.cpp  #   AT+CFSTERM / CFSINIT / CFSWFILE
│       ├── gnss.h/.cpp         #   AT+CGNSPWR / CGNSINF / starts / waitForFix
│       ├── http.h/.cpp         #   AT+SHCONF / SHBOD / SHREQ / SHREAD / SHDISC
│       ├── mqtt.h/.cpp         #   AT+SMCONF / SMSSL / SMCONN / SMPUB / SMSUB / SMDISC
│       ├── network.h/.cpp      #   AT+CFUN / CNMP / CMNB / CPIN / CGATT / CPSI / CNACT / CNCFG
│       ├── parser.h/.cpp       #   quoted CSV and response-line helpers
│       ├── pdp.h/.cpp          #   AT+CGATT / CGDCONT / CGACT / CGPADDR / CGAUTH
│       ├── power.h/.cpp        #   boot probe, power cycle, PSM/eDRX, reboot
│       ├── sim.h/.cpp          #   CPIN / CIMI / CCID / CNUM
│       ├── sms.h/.cpp          #   CMGF / CMGS / CMGL / CMGR / CMGD
│       ├── ssl.h/.cpp          #   CSSLCFG generic SSL context helpers
│       └── tcp_udp.h/.cpp      #   CA* thin TCP/UDP wrappers
├── json/                       # JSON payload helper  (libjson.a)
│   ├── json.hpp                #   nlohmann/json (bundled single-header)
│   ├── j.h                     #   createMqttPayload declaration
│   └── json.cpp                #   Payload builder
├── sim7080g_showcase.cpp        # Example application
└── CMakeLists.txt

Dependency order: at_commands ← sim7080g ← application

Quick Start

1 — Initialize the modem

#include "SIM7080G.h"
#include "power.h"

// Default config: UART0, GP0/GP1, power key GP14, 115200 baud
sim7080g_init();

// Register a handler for unsolicited result codes (e.g. MQTT messages)
sim7080g_set_urc_handler([](const std::string &line) {
    if (line.find("+SMSUB:") != std::string::npos)
        printf("MQTT message: %s\n", line.c_str());
});

check_start(); // probe, power-cycle if needed, retry up to 10×

2 — Attach to LTE Cat-M

#include "Network.h"

set_network(LTE_ONLY, CAT_M);   // AT+CNMP / AT+CMNB
check_network();                 // SIM PIN, signal, GPRS, APN, PDP activate

3 — Connect and publish via MQTT

#include "MQTT.h"
#include "json/j.h"

MqttConnectionConfig cfg;
cfg.host      = "your-broker.example.com";
cfg.port      = "1883";
cfg.client_id = "pico-001";
cfg.use_tls   = false;

mqttSetUpAndConnect(cfg);   // configure + connect, up to 10 retries

std::string payload = createMqttPayload(STATE, "online", cfg.client_id);
// → {"type":"state","data":"online","device_id":"pico-001"}

mqttPublishMessage("device/pico-001/state", payload);
mqttSubscribeToTopic("device/pico-001/cmd");

4 — Drive the URC loop

while (true) {
    process_uart_messages(); // dispatch any buffered URC lines
    sleep_ms(100);
}

TLS / mTLS

The SIM7080G stores TLS material in its own flash. The library uploads it over AT commands using AT+CFSWFILE.

Credential headers are excluded from version control by .gitignore. Use sim7080g/ssl_files/credentials.example.h as the template:

// credentials.h  (never commit this file)
static const unsigned char root_ca[]    = { /* DER bytes */ };
static const size_t        root_ca_len  = sizeof(root_ca);

static const unsigned char client_cert[]    = { /* DER bytes */ };
static const size_t        client_cert_len  = sizeof(client_cert);

static const unsigned char private_key[]    = { /* DER bytes */ };
static const size_t        private_key_len  = sizeof(private_key);

Then pass them to loadSSLFiles():

#include "FileSystem.h"
#include "ssl_files/credentials.h"

SIM7080GTlsCredentials creds;
creds.root_ca          = root_ca;
creds.root_ca_size     = root_ca_len;
creds.client_cert      = client_cert;
creds.client_cert_size = client_cert_len;
creds.private_key      = private_key;
creds.private_key_size = private_key_len;

loadSSLFiles(creds);

Set kUseTls = true and point MqttConnectionConfig::port at 8883 (or your broker's TLS port).

Showcase Application

sim7080g_showcase.cpp walks through the complete workflow end-to-end. Edit the constants at the top before flashing:

constexpr char kMqttHost[]       = "broker.example.com"; // ← your broker
constexpr char kMqttPort[]       = "1883";
constexpr char kMqttClientId[]   = "pico-sim7080g-demo";
constexpr char kPublishTopic[]   = "sim7080g/demo/state";
constexpr char kSubscribeTopic[] = "sim7080g/demo/config";
constexpr bool kUseTls           = false;

Flow:

stdio_init_all() — debug output on UART1 (GP4/GP5)
LED blink — visible boot indicator
sim7080g_init() + check_start() — probe modem, power-cycle if silent
get_battery_status() — log charge state and voltage
Safety gate: exits early if kMqttHost still contains example.com
set_network(LTE_ONLY, CAT_M) — configure radio
check_network() — wait for attachment and activate PDP
mqttSetUpAndConnect() — connect to broker
Publish {"type":"state","data":"online",...}
mqttSubscribeToTopic() — listen for inbound commands
Main loop: process_uart_messages() every 3 s dispatches URC lines

Expected serial output (115200 baud on GP4/GP5):

Start
Charge Status: 0
Battery Level: 87%
Voltage: 4102 mV
AT+CNMP=38 -> OK
AT+CMNB=1 -> OK
...
AT+SMCONN -> OK
AT+SMPUB="sim7080g/demo/state",... -> OK
AT+SMSUB="sim7080g/demo/config",0 -> OK

SIM7080G Configuration Reference

Key AT commands used by this library:

AT command	Purpose
`AT+CFUN`	Phone functionality (min / full / reset)
`AT+CNMP`	Preferred network mode (GSM / LTE / Auto)
`AT+CMNB`	Cat-M / NB-IoT selection
`AT+CPIN`	SIM PIN status / unlock
`AT+CSQ`	Signal quality report (RSSI / BER)
`AT+CGATT`	GPRS attachment status
`AT+CGDCONT`	3GPP PDP context configuration
`AT+CGACT`	3GPP PDP context activation
`AT+CGPADDR`	Read PDP address
`AT+CPSI`	UE system information (operator, band, RSRP)
`AT+CGNAPN`	Read network-provided APN
`AT+CNCFG`	PDP context configuration
`AT+CNACT`	Application network activation
`AT+SHCONF`	HTTP parameter configuration
`AT+SHBOD`	HTTP request body upload
`AT+SHREQ`	HTTP request
`AT+SHREAD`	HTTP response read
`AT+SMCONF`	MQTT parameter configuration
`AT+SMCONN`	MQTT connect
`AT+SMPUB`	MQTT publish
`AT+SMSUB`	MQTT subscribe
`AT+SMDISC`	MQTT disconnect
`AT+CSSLCFG`	SSL/TLS parameter configuration
`AT+SMSSL`	Bind SSL context to MQTT
`AT+CFSINIT`	Initialize modem file system buffer
`AT+CFSWFILE`	Write file to modem flash
`AT+CGNSPWR`	GNSS power
`AT+CGNSINF`	GNSS fix/status information
`AT+CMGF`	SMS format
`AT+CMGS`	SMS text send
`AT+CAOPEN`	TCP/UDP open
`AT+CASEND`	TCP/UDP send
`AT+CBC`	Battery and charge status
`AT+CPOWD`	Power down modem
`AT+CREBOOT`	Reboot modem
`AT+CSCLK`	Slow clock / sleep configuration
`AT+CPSMS`	3GPP Power Saving Mode
`AT+CEDRXS`	eDRX configuration

Full AT command reference: SIM7080G AT Command Manual

What Is Not Included

Unit tests with a mocked UART transport
Production reconnect / exponential-backoff state machine
Watchdog / health-monitor integration
Complete voice, FTP, CoAP, SIM Toolkit or vendor-special command coverage

License

MIT — see LICENSE.

Name		Name	Last commit message	Last commit date
Latest commit History 1 Commit
.vscode		.vscode
json		json
sim7080g		sim7080g
.gitignore		.gitignore
CMakeLists.txt		CMakeLists.txt
LICENSE		LICENSE
README.md		README.md
SECURITY.md		SECURITY.md
pico_sdk_import.cmake		pico_sdk_import.cmake
sim7080g_showcase.cpp		sim7080g_showcase.cpp

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Repository files navigation

SIM7080G Pico Library

Features

Hardware

Pin Defaults

Wiring

Dependencies

Build

Repository Layout

Quick Start

1 — Initialize the modem

2 — Attach to LTE Cat-M

3 — Connect and publish via MQTT

4 — Drive the URC loop

TLS / mTLS

Showcase Application

SIM7080G Configuration Reference

What Is Not Included

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SIM7080G Pico Library

Features

Hardware

Pin Defaults

Wiring

Dependencies

Build

Repository Layout

Quick Start

1 — Initialize the modem

2 — Attach to LTE Cat-M

3 — Connect and publish via MQTT

4 — Drive the URC loop

TLS / mTLS

Showcase Application

SIM7080G Configuration Reference

What Is Not Included

License

About

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