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

[Thomas Huth]

On 23/01/2023 19.07, Matwey V. Kornilov 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?

It's doable on some targets, e.g. m68k. avr seems to be working, too:

- You can specify a CPU with the "-cpu" command line option
  (use "-cpu help" for a list)

- You can specify a RAM region with the "-m" command line option
  (it will be created at address 0)

- You can load some code with the "loader" device
  (see "-device loader,help" for information how to use it)

For example:

wget 
https://github.com/seharris/qemu-avr-tests/raw/master/free-rtos/Demo/AVR_ATMega2560_GCC/demo.elf

$ ./qemu-system-avr -M none -cpu avr6-avr-cpu -m 512 -d in_asm \
  -device loader,file=demo.elf 2>&1 | head -n 15
----------------
IN:
0x00000000:  JMP       0x110

----------------
IN:
0x00000110:  EOR       r1, r1
0x00000112:  OUT       $63, r1
0x00000114:  LDI       r28, 255
0x00000116:  LDI       r29, 33
0x00000118:  OUT       $62, r29
0x0000011a:  OUT       $61, r28
0x0000011c:  LDI       r16, 0
0x0000011e:  OUT       $60, r16
0x00000120:  LDI       r17, 2

... of course you might also want to attach an avr GDB to QEMU to interact 
with the code, but I don't have such a GDB here right now, so no way to 
check whether that's working here or not.

 HTH,
  Thomas