Re: What is the purpose for "none" machine?

[Thomas Huth]

On 23/01/2023 21.03, Peter Maydell wrote:
> On Mon, 23 Jan 2023 at 18:07, Matwey V. Kornilov
> <matwey.kornilov@gmail.com> wrote:
> > пн, 23 янв. 2023 г. в 21:02, Peter Maydell <peter.maydell@linaro.org>:
> > > On Mon, 23 Jan 2023 at 17:36, Matwey V. Kornilov
> > > <matwey.kornilov@gmail.com> wrote:
> > > > I am playing with qemu-system-avr currently.
> > > > I see that there is an "empty machine" called "none" in
> > > >
> > > >       qemu-system-avr -M help
> > > >
> > > > list.
> > > >
> > > > Is it a real thing? I am failed to run any code with "none" machine.
> > >
> > > It is mostly for the benefit of management layer code (eg libvirt)
> > > that wants to probe capabilities of QEMU[*], and secondarily used
> > > in some of QEMU's own test suite.  The 'none' machine has no CPU,
> > > no devices and no RAM, which is why you can't run any code on it.
> >
> > Thanks for the explanation. Is there a way to manually add CPU, RAM
> > and other devices in the command line if 'none' is used?
>
> For a CPU and RAM, for some architectures where there is hotplug
> CPU and hotplug RAM support that might be possible (definitely
> not for AVR!) but I'm not sure if it's supported as an intended
> use case. For other devices, generally not.

Some people really only need a plain machine with CPU and RAM for testing 
instructions. So I've improved the "none" machine a couple of years ago to 
be used as plain instruction set simulator, see:

 https://gitlab.com/qemu-project/qemu/-/commit/3964ec6c0b49e4c2fa3e48f

(that way we were able to get rid of the "dummy" m68k machine which had 
exactly the same purpose). It seems to be working with avr, too.

 Thomas