[Qemu-devel] Modeling a device controlled by combination of GPIO and UART

[Martin Schroeder]

I'd like to add a virtual device that is controlled by a couple of
GPIO pins on my controller (cortex-m4) and a serial port. I suppose I
can derive it from SSISlaveClass to make the new device a serial
slave.

But how do I connect GPIOs?

I want the slave device to be notified when guest firmware toggles a
gpio pin through the gpio driver which is an mmio device mapped into
the gpio memory area. So the GPIO driver currently keeps the state of
the pins internal to the driver. What I would like to do is somehow,
without requiring that the GPIO driver knows about the connected slave
device, deliver the notification of a gpio pin being toggled to the
slave device.

How does qemu implement this kind of thing?