qemu-rpi-gpio 0.4

Simulate GPIOs in qemu-based Raspberry PI

QEMU RPI GPIO

Simulate GPIO in qemu-based Raspberry Pi

How it works

The script (qemu-rpi-gpio) present in this repository interacts with qemu using the built-in qtest protocol.

Wrapping the protocol and interacting with the memory of the guest operating system, it can set or reset the various GPIOs.

Note: Vanilla qemu (5.1.93) will not handle GPIO interrupts, therefore loading /sys/class/gpio/gpio$N/direction and waiting for an interrupt will not do anything.

To enable interrupt support you'll need to download and compile this qemu fork.

Installation

You can install the script via pip with

pip install qemu-rpi-gpio

Prereqisites

You need socat, python3 and pexpect library to use this script.

These can be installed under ubuntu with:

sudo apt install python3-pexpect socat

To download raspbian images you'll need 7zip

sudo apt install p7zip-full

Setup

Download a raspbian image using

./qemu-pi-setup/setup.sh

After this operation, execute the script to load the unix socket and make it available to qemu

./qemu-rpi-gpio

You will be prompted to an interactive shell, you can find the commands available in the Interacting with gpios section.

In another terminal execute the ./qemu-pi-setup/run.sh script, this will execute a virtual raspberry pi and attach it to the gpio application.

If you close the raspberry pi you can reload the socket using the command reload in the qemu-rpi-gpio prompt.

Interacting with gpios

First of all, you need to export GPIOs in your guest Linux. In a shell on your raspberry pi do:

$ sudo su -
# echo 4 >/sys/class/gpio/export
# echo in >/sys/class/gpio/direction

The main commands in the qemu-rpi-gpio application are:

command	description	example
get $N	get the value of GPIO $N	get 4
set $N $V	set the value of GPIO $N to $V (1 or 0)	set 4 1

You can get the full list of commands using help

For instance, let us set the value of the pre-exported gpio 4

(gpio)> set 4 1

Now you can read the value of your gpio

# cat /sys/class/gpio/value
1

If we set it to zero, it will be immediately reflected in the guest system

(gpio)> set 4 0

# cat /sys/class/gpio/value
0