Re: [PATCH v35 00/13] QEMU AVR 8 bit cores

[Philippe Mathieu-Daudé]

Hi Michael, Joaquin.

Michael: Joaquin asked at the KVM Forum how he can start contributing to 
QEMU, having an electronic background, and being custom the the AVR 
microprocessor. I told him about your ongoing work. Joaquin is 
interested in adding a new board to QEMU, and the Arduino would be his 
board of choice.

Joaquin: This is the series I was tell you about. This series will 
likely be merged during the 5.0 development window. It lacks a real 
hardware model. Michael and Sarah didn't wrote one because they focus on 
the architecture part, which is enough for them (to test that AVR GCC).

See below for more comments about the codebase organization.

On 10/29/19 10:24 PM, Michael Rolnik wrote:
> This series of patches adds 8bit AVR cores to QEMU.
> All instruction, except BREAK/DES/SPM/SPMX, are implemented. Not fully tested 
> yet.
> However I was able to execute simple code with functions. e.g fibonacci 
> calculation.
> This series of patches include a non real, sample board.
> No fuses support yet. PC is set to 0 at reset.
>
> the patches include the following
> 1. just a basic 8bit AVR CPU, without instruction decoding or translation
> 2. CPU features which allow define the following 8bit AVR cores
>       avr1
>       avr2 avr25
>       avr3 avr31 avr35
>       avr4
>       avr5 avr51
>       avr6
>       xmega2 xmega4 xmega5 xmega6 xmega7
> 3. a definition of sample machine with SRAM, FLASH and CPU which allows to 
> execute simple code
> 4. encoding for all AVR instructions
> 5. interrupt handling
> 6. helpers for IN, OUT, SLEEP, WBR & unsupported instructions
> 7. a decoder which given an opcode decides what istruction it is
> 8. translation of AVR instruction into TCG
> 9. all features together
[...]

>   MAINTAINERS                      |    9 +
>   arch_init.c                      |    2 +
>   configure                        |    7 +
>   default-configs/avr-softmmu.mak  |    5 +
>   gdb-xml/avr-cpu.xml              |   49 +

The part under hw/avr/ is the 'board' part.

You can take a AVR cpu, glue it with peripherals (mapping blocks and 
wiring IRQ), put it on a PCB ('board') and connect external devices.

You get a QEMU machine. You can load a ELF program directly to memory 
and execute it, or you can load a firmware from ROM/flash.

>   hw/Kconfig                       |    1 + >   hw/avr/Kconfig                  
>  |    6 +
>   hw/avr/Makefile.objs             |    1 +
>   hw/avr/sample.c                  |  282 +++
>   hw/char/Kconfig                  |    3 +
>   hw/char/Makefile.objs            |    1 +
>   hw/char/avr_usart.c              |  324 ++++
>   hw/misc/Kconfig                  |    3 +
>   hw/misc/Makefile.objs            |    2 +
>   hw/misc/avr_mask.c               |  112 ++
>   hw/timer/Kconfig                 |    3 +
>   hw/timer/Makefile.objs           |    2 +
>   hw/timer/avr_timer16.c           |  605 ++++++
>   include/disas/dis-asm.h          |    6 +
>   include/hw/char/avr_usart.h      |   97 +
>   include/hw/misc/avr_mask.h       |   47 +
>   include/hw/timer/avr_timer16.h   |   97 +
>   include/sysemu/arch_init.h       |    1 +
>   qapi/machine.json                |    3 +-

The files under target/avr/ are the architecture part.
Michael and Sarah run the GCC test suite on this, so this part should be 
quite correct and you shouldn't worry about looking here, except if some 
instruction behaves incorrectly. I strongly suggest you to stay focused 
with the files under hw/ and include/hw/.

>   target/avr/Makefile.objs         |   33 +
>   target/avr/cpu-param.h           |   37 +
>   target/avr/cpu-qom.h             |   54 +
>   target/avr/cpu.c                 |  576 ++++++
>   target/avr/cpu.h                 |  253 +++
>   target/avr/gdbstub.c             |   85 +
>   target/avr/helper.c              |  354 ++++
>   target/avr/helper.h              |   29 +
>   target/avr/insn.decode           |  175 ++
>   target/avr/machine.c             |  121 ++
>   target/avr/translate.c           | 3028 ++++++++++++++++++++++++++++++
>   tests/Makefile.include           |    2 +
>   tests/acceptance/machine_avr6.py |   36 +
>   tests/boot-serial-test.c         |   10 +
>   tests/machine-none-test.c        |    1 +
>   39 files changed, 6461 insertions(+), 1 deletion(-)

Hope this helps a bit to start looking at QEMU.

You are welcome to ask any question on this list or on IRC.

Regards,

Phil.