On 22 August 2018 at 08:36, Martin Schroeder <mkschreder...@googlemail.com> wrote: > Thanks Peter. > > I have set it up such that master device has qemu_irq array which it > initializes using qdev_init_gpio_out with number of gpio lines going > out and slave device calls qdev_init_gpio_in with a callback that > should be called when irq is raised. Then I connect them together at > higher level using qdev_connect_gpio_out as you said. Then master > calls qemu_set_irq with 1 or 0 depending on whether the gpio is high > or low. > > This works, but not as I would expect. The handler that I supply to > the init_gpio_in is only being called very infrequently - perhaps once > every 50 toggles on the gpio pin. I need to make sure that it gets > called every time master device calls qemu_set_irq. > > What's the mechanism behind this behavior and how can I deliver gpio > change to the slave?
The mechanism is pretty simple -- a qemu_irq is really a pointer to a small struct that has a function pointer in it. Initializing a gpio in is just setting up the struct and function pointer. Connecting them is passing the qemu_irq pointer to the source. Calling qemu_set_irq() simply calls the function pointer. (You can step through in a debugger from the qemu_set_irq call through to the target function call if you like -- it's not very much code.) This can fail in the sense that if you don't wire it up right then nothing happens when you call qemu_set_irq() (because you didn't give the source device the right qemu_irq or you didn't give it one at all), but it shouldn't be able to fail unreliably and only call the destination handler some of the time. thanks -- PMM
