sim7600-aws-mqtt

A portable C library for using SIMCom SIM7600 cellular modems with AWS IoT Core MQTT over the modem's native TLS stack. Two platform ports ship in the same repo: a generic STM32 HAL port (reference example on a Nucleo-F412ZG, family agnostic) and a Teensy 4.1 (Arduino) port.

Status

Pre release, version 0.0.1. The path to v0.1.0 is tracked in the Roadmap below.

What works today, locally verified:

• Platform agnostic AT command engine in C99 with host unit tests covering OK, ERROR, timeout, multi line response, and URC interleaved with a pending command.
• Generic STM32 HAL port, family agnostic. Freestanding subset of the core compiles cleanly under arm-none-eabi-gcc.
• Teensy 4.1 (Arduino) port. arduino-cli compile of the example sketch is clean.

Pending hardware bench verification:

• STM32 example on a Nucleo-F412ZG talks to a SIM7600G-H and prints AT -> OK on the ST-Link VCP at 115200.
• Teensy 4.1 example talks to a SIM7600G-H and prints AT -> OK on USB Serial at 115200.

Not yet implemented (path to v0.1.0):

• Cellular network registration plus APN bring up (M4).
• Native modem TLS plus AWS root CA, client cert, and key provisioning (M5).
• MQTT publish, subscribe, and exponential backoff reconnect (M6).
• End to end AWS IoT publisher example on both platforms (M7).
• CI plus the v0.1.0 release tag (M8).

Architecture

core/                  Platform agnostic C99
  sim7600_at           AT command engine, URC dispatch, line based parser
  sim7600_ringbuf      Single producer single consumer byte ring buffer
  sim7600_port.h       Platform interface contract (the only seam)

port/stm32_hal/        Generic STM32 HAL implementation, family agnostic
port/teensy/           Teensy 4.1 (Arduino) implementation, C++ shim with extern "C"

examples/              One example per platform
tests/                 Host gcc unit tests with a mock port
src/                   Arduino library entry; symlinks into core and port/teensy

The core compiles as C99 with no platform headers. It does not include any STM32 HAL header, any Arduino header, or any other platform header. The only seam is sim7600_port.h. The same core links unmodified against both ports.

Quick start

Teensy 4.1

brew install arduino-cli
arduino-cli config init
arduino-cli config add board_manager.additional_urls https://www.pjrc.com/teensy/package_teensy_index.json
arduino-cli core update-index
arduino-cli core install teensy:avr

git clone https://github.com/ankitvirdi4/sim7600-aws-mqtt
cd sim7600-aws-mqtt
arduino-cli compile --fqbn teensy:avr:teensy41 --library . examples/teensy41_aws_publisher
arduino-cli upload  --fqbn teensy:avr:teensy41 --port /dev/cu.usbmodem* examples/teensy41_aws_publisher

Wiring, USB type, and serial expectations are in examples/teensy41_aws_publisher/README.md.

On Apple Silicon Macs, the Teensy core ships x86_64 binaries that need Rosetta 2: softwareupdate --install-rosetta --agree-to-license.

STM32 (Nucleo-F412ZG via STM32CubeIDE)

1. STM32CubeIDE: New STM32 Project, Board Selector, NUCLEO-F412ZG, accept defaults.
2. Replace Core/Src/main.c with examples/stm32f412_nucleo_aws_publisher/Core/Src/main.c.
3. Add examples/stm32f412_nucleo_aws_publisher/Core/Inc/stm32_hal_glue.h.
4. Add core/ and port/stm32_hal/ to the project's include and source paths.
5. Build, flash, observe USART3 (the ST-Link VCP) at 115200 8N1.

Wiring, CubeMX configuration, and troubleshooting are in examples/stm32f412_nucleo_aws_publisher/README.md. Other STM32 families work with the same port code; the only family decision is one #include in stm32_hal_glue.h.

Roadmap

The library is being built milestone by milestone, with hardware verification at each step.

• M1, done: AT engine plus host tests.
• M2, code complete, hardware verification pending: STM32 port plus Nucleo-F412ZG echo example.
• M3, code complete, hardware verification pending: Teensy 4.1 port plus echo sketch.
• M4, next: cellular network registration plus APN bring up. Three UK as the reference carrier.
• M5: native modem TLS via AT+CSSLCFG and AT+CCERTDOWN; AWS root CA, client cert, and private key uploaded to modem flash.
• M6: MQTT publish, subscribe, and exponential backoff reconnect via AT+CMQTT*.
• M7: end to end AWS IoT publisher on both platforms, telemetry every 10 seconds.
• M8: GitHub Actions CI (host tests, multi family STM32 compile, Teensy compile) plus the v0.1.0 release tag.
• M9: announcement on Medium, Hackster, and r/embedded.

QoS 1 ships in v0.1.0 if M6 stays inside its time budget; otherwise it slips to v0.2.0 and the limitation is documented.

Repo layout

• core/ and port/ are the library proper.
• examples/ has one example project per platform.
• tests/ has host side unit tests with a mock port and a Makefile that runs them under host gcc and an arm cross compile sanity check.
• src/ is the Arduino library entry, populated by symlinks into core/ and port/teensy/. The same code is the canonical source; the symlinks just expose the Teensy slice in the layout arduino-cli and the Arduino IDE expect.
• docs/reference/ holds the SIM7600 AT command manual that the higher milestones will reference.
• CLAUDE.md is the working spec and house rules; read it first if you plan to contribute.

License

MIT, copyright (c) 2026 Ankit Virdi. See LICENSE.

Contributing

Issues and PRs welcome. The easiest contribution is hardware diversity: an additional STM32 board (any family covered by the generic HAL port), an additional Teensy variant, or a wiring photo for a board that is not yet documented. The next easiest is documentation; if a step in either example README is unclear or wrong, a short PR with a fix is the right answer.

For source changes please follow the conventions in CLAUDE.md.