m33mu

m33mu is an embedded microcontroller emulator for ARMv8-M Cortex-M33 targets. It is used to test, debug, and demonstrate firmware without any physical hardware.

It can run as:

• an interactive terminal UI with --tui
• a pure command-line emulator
• a tool inside automated tests and CI jobs

What It Does

• Emulates Cortex-M33 / ARMv8-M firmware with TrustZone awareness
• Runs firmware images directly from your host machine
• Supports debugging through a built-in GDB remote server
• Can load multiple images, including Secure and Non-secure firmware combinations
• Exposes UART, SPI flash, TPM, TA-100, ATECC608A, SE050, STSAFE-A120, and IoTSAFE modem+SIM secure-element paths, plus USB, Ethernet, and other target-specific peripherals
• Ships SoC profiles for STM32H5/U5/L5, NXP LPC55S69, MCXW71C, MCXN947, RW612 (with ELS/PKA crypto offload), Nordic nRF5340 / nRF54LM20, RP2350, and Microchip PIC32CK — see supported CPUs for the full list

Note: ATECC608A, SE050, and STSAFE-A120 simulation requires cargo (Rust toolchain) at build time. These features are automatically disabled if cargo is not found.

Documentation Index

• Getting started
• Supported CPUs
• Loading images
• Command-line usage
• Supported HSE simulators
• CI and automated testing

Example

Run the STM32H563 wolfSSL IoTSAFE mutual-TLS demo against the built-in modem+SIM emulator on USART3:

build/m33mu \
  --cpu stm32h563 \
  --uart-stdout \
  --expect-bkpt 0x42 \
  --timeout 20 \
  --iotsafe-uart:0x40004800:file=/tmp/m33mu-iotsafe-sim.bin \
  tests/firmware/test-stm32h563-wolfssl-iotsafe/app.bin

This exercises wolfSSL's 16-bit IoTSAFE _ex API path for SIM-backed certificate reads, RNG, ECC sign/verify, ECDH, and an end-to-end mTLS handshake.

Screenshots for TUI mode

m33mu TUI, stopped, stepping with GDB:

m33mu TUI, running in secure domain:

m33mu TUI, running in non-secure domain:

Reporting Issues

Please report issues to the GitHub issue tracker.

Include, if possible, a full capture using --capstone, a reproducer firmware image, and a clear explanation of how to reproduce the problem.

Copyright / License

Copyright (c) Daniele Lacamera 2025.

Released under AGPLv3. See LICENSE.