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From: Ajay Garg <ajaygargnsit@gmail.com>
Date: Mon, 9 Apr 2018 23:32:57 +0530
Message-ID: <CAHP4M8WLXqvCVGxVyaTiCQbwcJVXEPCnRL1DTzzNZq1Cbu0v1w@mail.gmail.com>
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Subject: Re: [Qemu-devel] [Qemu-arm] Use of -machine when running via
 qemu-system-arm
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-arm <qemu-arm@nongnu.org>, QEMU Developers <qemu-devel@nongnu.org>

Thanks a ton Peter, that cleared things up a great deal !!!
Thanks again for the quick help !!


Thanks and Regards,
Ajay

On Mon, Apr 9, 2018 at 11:17 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 9 April 2018 at 18:41, Ajay Garg <ajaygargnsit@gmail.com> wrote:
>> Hi Peter.
>>
>> The link is pretty good, just that I am a complete noob.
>>
>> Maybe a more concrete example on the following, clearly specifying why
>> things work on x86 without the need of -machine flag, will make things
>> crystal clear :
>>
>> Because ARM systems differ so much and in fundamental ways, typically
>> operating system or firmware images intended to run on one machine
>> will not run at all on any other. This is often surprising for new
>> users who are used to the x86 world where every system looks like a
>> standard PC. (Once the kernel has booted, most userspace software
>> cares much less about the detail of the hardware.)
>
> For instance, on x86 you can always find the UART for serial
> output at IO port 0x3f8, and it's always an 8250 or compatible.
> On Arm, the memory address where the UART is will be likely
> different for every board. And once you know the address of the
> UART, each SoC likely may well have its own implementation,
> which has different registers that do different things.
> And there's no way to probe for what's there -- you have to
> know in advance. So you can't even usefully print bootup
> messages without knowing what you're running on.
>
> thanks
> -- PMM