qemu-rpi-gpio 0.3

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

Wait a little time, I'm pushing to pip :)

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