Re: [Qemu-devel] [RFC] qapi: command category to stimulate high-level machine devices

[Stefan Hajnoczi]

On Mon, Jun 04, 2018 at 05:14:25PM -0500, Eric Blake wrote:
> On 06/01/2018 10:16 PM, Steffen Görtz wrote:
> > From: Steffen Goertz <address@hidden>
> > 
> > Add a new category "stimulate" to host commands that
> > act upon high-level devices associated with machines/boards.
> > 
> > This is patch is part of an effort to add support for BBC:microbit
> > educational computer to QEMU.
> > 
> > The microbit board, as many other microcontroller boards,
> > contains typical trivial (digital) input and output options such as buttons 
> > and LEDs,
> > but also more sophiscated possibilities such as analog inputs and
> 
> s/sophiscated/sophisticated/
> 
> > complex dedicated sensor ICs that are connected to the microbit machine
> > by means of inter-ic bus (i2c).
> > These devices interact with peripheral devices of the microcontroller
> > in use, for example with the GPIO peripheral of the used NRF51.
> > 
> > One aim of our efforts is to create a user interface that models the
> > look and feel of the physical microbit board and lets the user interact
> > with its inputs and provide feedback on its outsputs.
> 
> s/outsputs/outputs/
> 
> > 
> > For this it is necessary to transmit user inputs such as the pressing of a
> > button to the machine.
> > In return, when the state of an output is changed on the machine, this
> > change needs to be reflected in the user interface.
> > 
> > At the moment, there are only a few QMP commands that provide user input to 
> > the
> > machine, eg. send-keys, input-button. These commands require very
> > high-level concepts, which are not really suitable for applications that
> > microcontrollers are typically used in in.
> > 
> > This RFC is meant to start a discussion on how to provide stimuli to
> > low-complex inputs and outputs typically found in embedded
> > microcontroller applications. To the best of my knowledge, there are
> > currently no examples of how to provide such stimuli to either SoC
> > device peripheral or machine level concepts like pushbuttons and LEDs.
> > 
> > To my understanding, the following concepts/apis are needed:
> > - QMP commands to send stimuli to machine level concepts like
> > pushbuttons
> > - Machine level devices that receive these stimuli and act as an adapter
> > to manipulate the associated SoC peripheral devices
> > - For outputs, machine level devices are needed that observe changes in
> > SoC peripherals and emit QMP events that clients can receive
> > 
> > This patch adds a new qmp command "buttons-set-state" to update the
> > push-down state of arbitrarily identified buttons (string identifier).
> 
> An arbitrary string has the most flexibility, but also the least
> discoverability.  Is there any way to enumerate which strings are valid,
> and/or make the button names an enum instead of an open-coded string?

The button names could defined by an enum.

Which button names are valid with a particular machine type can't be
expressed in the schema AFAIK.

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