[Qemu-devel] implementing ARM926EJ-S support

[Qemu-devel] implementing ARM926EJ-S support

[Alessandro]

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Hi all!
I am an experencied QEMU user.
Although I am a good C/C++ programmer, I have only theoretic/basic knowledge 
about virtual machines programming.
For study, I'm thinking to write a simple VM that can simulate an ARM SoC based 
on ARM926EJ-S core.

I have basically two choice: 

1- build all from scratch, full-simulating core and peripherals;
2- modify a pre-existing VM with ARM architecture support(QEMU).

Second option can be a viable way? 

Thanks in advance

IT

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Re: [Qemu-devel] implementing ARM926EJ-S support

[Peter Maydell]

On 2 May 2011 02:53, Alessandro <hyperboreus2002@yahoo.it> wrote:
> For study, I'm thinking to write a simple VM that can simulate an ARM SoC
> based on ARM926EJ-S core.
>
> I have basically two choice:
>
> 1- build all from scratch, full-simulating core and peripherals;
> 2- modify a pre-existing VM with ARM architecture support(QEMU).
>
> Second option can be a viable way?

QEMU already implements an ARM926 model, so all you'd have to
implement would be the peripheral models for whatever SoC
you had in mind. That sounds much easier to me :-)

-- PMM

Re: [Qemu-devel] implementing ARM926EJ-S support

[Alessandro]

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Thanks for your reply, Peter. :-)
Thanks for giving me good news.

According to what you say, would be better to pick QEMU source code, adding some 
peripherals and enjoy. 

ARM core-related code appears to be located (mainly)under ARM directory; 
peripherals-related files should be located under "machine" dir.

I still have some questions about QEMU ARM926 support: 

1- What standard extensions are supported? e.g Jazelle.

2- Sometimes, SoC includes "inusual"(and _poorly_ documented) hardware: ISP, 
video Coproc, and so on.
This increase significantly the final complexity of project. What are the 
"guidelines" to follow? What must be implemented, and what could be safely 
ignored?

Eventually, any indication - references to (official)docs included - would be 
appreciated. :-)

IT




________________________________
Da: Peter Maydell <peter.maydell@linaro.org>
A: Alessandro <hyperboreus2002@yahoo.it>
Cc: qemu-devel@nongnu.org
Inviato: Lun 2 maggio 2011, 10:04:18
Oggetto: Re: [Qemu-devel] implementing ARM926EJ-S support

On 2 May 2011 02:53, Alessandro <hyperboreus2002@yahoo.it> wrote:
> For study, I'm thinking to write a simple VM that can simulate an ARM SoC
> based on ARM926EJ-S core.
>
> I have basically two choice:
>
> 1- build all from scratch, full-simulating core and peripherals;
> 2- modify a pre-existing VM with ARM architecture support(QEMU).
>
> Second option can be a viable way?

QEMU already implements an ARM926 model, so all you'd have to
implement would be the peripheral models for whatever SoC
you had in mind. That sounds much easier to me :-)

-- PMM

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Re: [Qemu-devel] implementing ARM926EJ-S support

[Peter Maydell]

On 2 May 2011 13:46, Alessandro <hyperboreus2002@yahoo.it> wrote:
> ARM core-related code appears to be located (mainly)under ARM directory;
> peripherals-related files should be located under "machine" dir.

I'm not sure what source tree you're looking at. Code for ARM core
as a target is in target-arm/. Device models are in hw/. (tcg/arm
is support for emulating other CPUs on an ARM host, so not relevant
for you.)

> I still have some questions about QEMU ARM926 support:
>
> 1- What standard extensions are supported? e.g Jazelle.

We don't support Jazelle. We don't implement the TCMs (in the same
way we don't implement caches). We probably don't get all the
device-specific cp15 registers right. (None of that is likely to be
of any practical importance.) I can't see anything else missing from
a quick scan.

The rough rule of thumb for support is "if Linux uses it it's almost
certainly supported; otherwise it might be missing or broken" :-)

> 2- Sometimes, SoC includes "inusual"(and _poorly_ documented) hardware: ISP,
> video Coproc, and so on.
> This increase significantly the final complexity of project. What are the
> "guidelines" to follow? What must be implemented, and what could be safely
> ignored?

Well, if you're just doing things for your own amusement you can
implement or leave out what you like. For things to be included
in QEMU my personal opinion (I don't have a veto or anything) would
be that the question is whether there's any benefit to the new
SoC model that the existing ones don't provide -- is it some
common piece of hardware that a lot of people own and might want
to use a model of, for example? If you pass that hurdle then there
is presumably an OS and set of applications that run on the real
hardware, and the minimum level of peripheral support would be
"enough to run that".

What SoC are you planning to model? I assume you have one in
mind since you were specific about wanting the ARM926 rather
than a more recent ARM core...

-- PMM

Re: [Qemu-devel] implementing ARM926EJ-S support

[Антон Кочков]

Alessandro, I think you can try add support for one of the Qualcomm
MSM6100, MSM6125, MSM6225, MSM6245, MSM6250, MSM6255A, MSM6260,
MSM6275, MSM6280, MSM6300, MSM6500, MSM6800;
Of course, if you dont know yet which you want.

Best regards,
Anton Kochkov.




On Tue, May 3, 2011 at 01:04, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 2 May 2011 13:46, Alessandro <hyperboreus2002@yahoo.it> wrote:
>> ARM core-related code appears to be located (mainly)under ARM directory;
>> peripherals-related files should be located under "machine" dir.
>
> I'm not sure what source tree you're looking at. Code for ARM core
> as a target is in target-arm/. Device models are in hw/. (tcg/arm
> is support for emulating other CPUs on an ARM host, so not relevant
> for you.)
>
>> I still have some questions about QEMU ARM926 support:
>>
>> 1- What standard extensions are supported? e.g Jazelle.
>
> We don't support Jazelle. We don't implement the TCMs (in the same
> way we don't implement caches). We probably don't get all the
> device-specific cp15 registers right. (None of that is likely to be
> of any practical importance.) I can't see anything else missing from
> a quick scan.
>
> The rough rule of thumb for support is "if Linux uses it it's almost
> certainly supported; otherwise it might be missing or broken" :-)
>
>> 2- Sometimes, SoC includes "inusual"(and _poorly_ documented) hardware: ISP,
>> video Coproc, and so on.
>> This increase significantly the final complexity of project. What are the
>> "guidelines" to follow? What must be implemented, and what could be safely
>> ignored?
>
> Well, if you're just doing things for your own amusement you can
> implement or leave out what you like. For things to be included
> in QEMU my personal opinion (I don't have a veto or anything) would
> be that the question is whether there's any benefit to the new
> SoC model that the existing ones don't provide -- is it some
> common piece of hardware that a lot of people own and might want
> to use a model of, for example? If you pass that hurdle then there
> is presumably an OS and set of applications that run on the real
> hardware, and the minimum level of peripheral support would be
> "enough to run that".
>
> What SoC are you planning to model? I assume you have one in
> mind since you were specific about wanting the ARM926 rather
> than a more recent ARM core...
>
> -- PMM
>
>

Re: [Qemu-devel] implementing ARM926EJ-S support

[Alessandro]

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> I'm not sure what source tree you're looking at. Code for ARM core
> as a target is in target-arm/. 

Exactly that.


> We don't support Jazelle. We don't implement the TCMs (in the same
> way we don't implement caches). We probably don't get all the
> device-specific cp15 registers right. (None of that is likely to be
> of any practical importance.)

 I have noticed that fully-simulating TCMs could be very difficult too.
My first trouble - for now - is: I can not distinguish beetween _CRITICAL_ 
features(that must be implemented) and _OPTIONAL_ features which can be omitted 
for simplicity.

> What SoC are you planning to model? I assume you have one in
> mind since you were specific about wanting the ARM926 rather
> than a more recent ARM core...

I was originally thinking to TI-DM365: as you can see, this SoC includes several 
_inusual_ peripherals, other than main core ARM926.

Linux runs on it: https://linuxlink.timesys.com/dev_center/dm365

IT

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Re: [Qemu-devel] implementing ARM926EJ-S support

[Alessandro]

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Hi, Anton.
Your proposal is also interesting :-)

It is well-documented hardware?

IT




________________________________
Da: Антон Кочков <anton.kochkov@gmail.com>
A: Peter Maydell <peter.maydell@linaro.org>
Cc: Alessandro <hyperboreus2002@yahoo.it>; qemu-devel@nongnu.org
Inviato: Mar 3 maggio 2011, 00:04:13
Oggetto: Re: [Qemu-devel] implementing ARM926EJ-S support

Alessandro, I think you can try add support for one of the Qualcomm
MSM6100, MSM6125, MSM6225, MSM6245, MSM6250, MSM6255A, MSM6260,
MSM6275, MSM6280, MSM6300, MSM6500, MSM6800;
Of course, if you dont know yet which you want.

Best regards,
Anton Kochkov.




On Tue, May 3, 2011 at 01:04, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 2 May 2011 13:46, Alessandro <hyperboreus2002@yahoo.it> wrote:
>> ARM core-related code appears to be located (mainly)under ARM directory;
>> peripherals-related files should be located under "machine" dir.
>
> I'm not sure what source tree you're looking at. Code for ARM core
> as a target is in target-arm/. Device models are in hw/. (tcg/arm
> is support for emulating other CPUs on an ARM host, so not relevant
> for you.)
>
>> I still have some questions about QEMU ARM926 support:
>>
>> 1- What standard extensions are supported? e.g Jazelle.
>
> We don't support Jazelle. We don't implement the TCMs (in the same
> way we don't implement caches). We probably don't get all the
> device-specific cp15 registers right. (None of that is likely to be
> of any practical importance.) I can't see anything else missing from
> a quick scan.
>
> The rough rule of thumb for support is "if Linux uses it it's almost
> certainly supported; otherwise it might be missing or broken" :-)
>
>> 2- Sometimes, SoC includes "inusual"(and _poorly_ documented) hardware: ISP,
>> video Coproc, and so on.
>> This increase significantly the final complexity of project. What are the
>> "guidelines" to follow? What must be implemented, and what could be safely
>> ignored?
>
> Well, if you're just doing things for your own amusement you can
> implement or leave out what you like. For things to be included
> in QEMU my personal opinion (I don't have a veto or anything) would
> be that the question is whether there's any benefit to the new
> SoC model that the existing ones don't provide -- is it some
> common piece of hardware that a lot of people own and might want
> to use a model of, for example? If you pass that hurdle then there
> is presumably an OS and set of applications that run on the real
> hardware, and the minimum level of peripheral support would be
> "enough to run that".
>
> What SoC are you planning to model? I assume you have one in
> mind since you were specific about wanting the ARM926 rather
> than a more recent ARM core...
>
> -- PMM
>
>

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Re: [Qemu-devel] implementing ARM926EJ-S support

[Andreas Färber]

Hi,

Am 03.05.2011 um 14:56 schrieb Alessandro:

>> What SoC are you planning to model? I assume you have one in
>> mind since you were specific about wanting the ARM926 rather
>> than a more recent ARM core...
>>
>
> I was originally thinking to TI-DM365: as you can see, this SoC  
> includes several _inusual_ peripherals, other than main core ARM926.
>
> Linux runs on it: https://linuxlink.timesys.com/dev_center/dm365

Have you checked if some QEMU fork already emulates the Leopardboard  
365? [1]
At least the BeagleBoard is available somewhere, not sure about the  
other animals.

Andreas

[1] http://designsomething.org/leopardboard/default.aspx

Re: [Qemu-devel] implementing ARM926EJ-S support

[Peter Maydell]

On 8 May 2011 16:39, Andreas Färber <andreas.faerber@web.de> wrote:
> Have you checked if some QEMU fork already emulates the Leopardboard 365?

> At least the BeagleBoard is available somewhere, not sure about the other
> animals.

Beagle is a different SoC (OMAP3). I have a patchstack with omap3
support in qemu-linaro that I need to clean up and submit for review.
There might be some other tree with leopard support, of course.

-- PMM