---
title: "Emulator and continuous integration"
---

# Emulator and continuous integration

Running and debugging the firmware image in QEMU for software-in-the-loop runs and continuous integration, how the emulated machine is chosen, and what the emulator does not model.

When no board is free, or in a CI pipeline, the firmware image can run in QEMU (`qemu-system-arm` 4.1 or later) on the engineer's machine: software-in-the-loop runs with semihosting output in the Debug Console, and debugging through QEMU's GDB stub.

## Run and debug

- **Run in Emulator** runs the active image in QEMU until it exits through semihosting, with its output in the Debug Console. In a launch configuration, **Run Firmware in Emulator** does the same.
- **Debug in Emulator**, or the snippet **Embedded: Debug Firmware in Emulator**, starts QEMU halted under its GDB stub, resets it through its monitor and debugs the image with GDB, with the same debug views as a session on a probe.

In `launch.json`, `"target": "emulator"` and an optional `"machine"` do the same, and a Cortex-Debug configuration with `servertype` `qemu` also runs:

```json
{
  "type": "ni-embedded",
  "request": "launch",
  "name": "Debug Firmware in Emulator",
  "target": "emulator",
  "machine": "netduinoplus2",
  "runToEntryPoint": "main"
}
```

## Which machine is used

The machine is chosen from what QEMU's own documentation states for the device and what the installed QEMU lists (`-machine help`): the STM32F405, F205, F100 and L475, two Stellaris parts and the nRF51.

**QEMU does not emulate the STM32F407.** Such a device gets a generic Cortex-M board, or a machine you name such as `netduinoplus2` (an STM32F405), only after you accept a message that its peripherals and memory map are not the chip's. The Debug Console repeats this when the session starts.

What the emulator does not model: the emulated chip's UART output is not shown, QEMU has no DWT (so the cycle stopwatch and benchmark counters report no counter), and there is no SWO or RTT.

## State

**Run in Emulator is verified against real QEMU 9.1.1** on macOS with a hand-built STM32F405 image of a few dozen bytes on the `netduinoplus2` machine: launch halted under the GDB stub, reset through its monitor, run to a semihosting exit. The machine choice is tested on recorded `-machine help` output of QEMU 9.1.1. **Debug in Emulator itself has not run with GDB in a verified audit.** Separately, debug sessions against QEMU 8.2.2's GDB stub with gdb-multiarch 15.1 on Linux were used to verify later views (memory windows, set-up scripts, ORTI, Heap and Stack, the buffer graph, the release comparison). Not verified: a real firmware image, QEMU on Windows, versions other than those named, and a CI pipeline running it.