Re: [Qemu-devel] [PATCH 3/3] target-xtensa: xtfpga: support noMMU cores

[Max Filippov]

On Mon, Sep 28, 2015 at 12:59 AM, Peter Crosthwaite
<address@hidden> wrote:
> On Sun, Sep 27, 2015 at 2:48 PM, Max Filippov <address@hidden> wrote:
>> On Mon, Sep 28, 2015 at 12:28 AM, Peter Crosthwaite
>> <address@hidden> wrote:
>>> To clarify, can you tell me the QEMU command line difference between
>>> MMU and noMMU?
>>
>> There is no difference. You specify -cpu without full MMU -- you get
>> noMMU address space layout.
>
> Ok but I think this is what we want to avoid. Using -cpu to switch up
> the board/SoC architecture. The address space layout is SoC level (and
> in your case a bitstream constitutes and entire SoC). There's a
> lengthy discussion on this here:
>
> http://lists.gnu.org/archive/html/qemu-devel/2013-11/msg03979.html
>
> going back and forth from that point in the thread. Your hardware
> model is more accurate that what was proposed by OP in that thread,
> but it is good to keep the interfaces consistent with other machine
> models.

The message by the link says:

  As Andreas says, we need to model real actual hardware,
  not some abstraction that kind of matches the kernel's
  abstractions.

Changing address space layout according to CPU type is what happens
in actual hardware. There are no user-controllable settings that would
allow mismatching address space layout and CPU type on XTFPGA
boards. There's also no SoC level mentioned in the developer guides
for the corresponding boards. So I'm not sure what you're proposing to do.

-- 
Thanks.
-- Max