Re: Qemu API documentation

["Alex Bennée" <alex.bennee@linaro.org>]

Priyamvad Acharya <priyamvad.agnisys@gmail.com> writes:

> Thanks John and Peter for guiding me, but still it will be hard to
> understand from source code for a newbie.
>
> I basically want to implement a trivial device for arm architecture which
> basically contains register for read/write operation with a program.So what
> are the references?

I would look at hw/misc/unimp.c as a useful template for implementing a
new device. Many boards instantiate the unimp devices for areas of SoC's
that are not yet implemented ;-) 

>
> I am providing pointers about my device which I am trying to implement:
>  - I am implementing a device which will be attached to *versatilepb*
> board, that board has* ARM926 CPU*.
> - My device name is "*soc*" , whose description is in *qemu/hw/misc/soc.c*
> file attached below.
> - I have written below line to make my device available to qemu in
> *qemu/hw/misc/Makefile.objs*.
>
>> *$ common-obj-$(CONFIG_SOC) += soc.o *
>>
> - I added following lines in *qemu/hw/arm/versatilepb.c* to attach my
> device to board.
>
>>
>> *#define DES_BASEADDR        0x101f5000*
>>
>>
>>
>> *    soc=qdev_create(NULL, "soc");// +    qdev_init_nofail(soc);// +
>> sysbus_mmio_map(SYS_BUS_DEVICE(soc), 0, DES_BASEADDR);// +*
>>
>
> - Run below commands to build my device
>
>> *$ make distclean*
>> *$ make -j8 -C build *
>>
>
> - Run below command to run a bare metal program on device.
>
>> *$ ./qemu-system-arm -M versatilepb -nographic -kernel
>> /lhome/priyamvad/debian_qemu_arm32/c_application/DES/des_demo.elf*
>>
>
> -I get following output in terminal shown below
>
>>
>>
>> *[priyamvad@predator arm-softmmu]$ ./qemu-system-arm -M versatilepb
>> -nographic -kernel
>> /lhome/priyamvad/debian_qemu_arm32/c_application/DES/des_demo.elf
>> qemu-system-arm: Unknown device 'soc' for default sysbusAborted (core
>> dumped)*
>>
>
> -Here des_demo.elf is our *bare metal program* executable for *arm(926ej-s)*
> processor.
>
> So how to resolve below issue to run executable
>
>>
>>
>> *[priyamvad@predator arm-softmmu]$ ./qemu-system-arm -M versatilepb
>> -nographic -kernel
>> /lhome/priyamvad/debian_qemu_arm32/c_application/DES/des_demo.elf
>> qemu-system-arm: Unknown device 'soc' for default sysbusAborted (core
>> dumped)*
>>
>
> test.s,test.ld,startup.S,Makefile,des_demo.c are files required for bare
>> metal program
>>
>
> References:
>
> https://devkail.wordpress.com/2014/12/16/emulation-of-des-encryption-device-in-qemu/
>
> Thanks,
> Priyamvad
>
> On Thu, 19 Mar 2020 at 01:19, John Snow <jsnow@redhat.com> wrote:
>
>>
>>
>> On 3/18/20 7:09 AM, Peter Maydell wrote:
>> > On Wed, 18 Mar 2020 at 09:55, Priyamvad Acharya
>> > <priyamvad.agnisys@gmail.com> wrote:
>> >>
>> >> Hello developer community,
>> >>
>> >> I am working on implementing a custom device in Qemu, so to implement
>> it I need documentation of functions which are used to emulate a hardware
>> model in Qemu.
>> >>
>> >> What are the references to get it ?
>> >
>> > QEMU has very little documentation of its internals;
>> > the usual practice is to figure things out by
>> > reading the source code. What we do have is in
>> > docs/devel. There are also often documentation comments
>> > for specific functions in the include files where
>> > those functions are declared, which form the API
>> > documentation for them.
>> >
>>
>> ^ Unfortunately true. One thing you can do is try to pick an existing
>> device that's close to yours -- some donor PCI, USB etc device and start
>> using that as a reference.
>>
>> If you can share (broad) details of what device you are trying to
>> implement, we might be able to point you to relevant examples to use as
>> a reference.
>>
>> --js
>>
>>


-- 
Alex Bennée