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

[Max Filippov]

On Thu, Oct 1, 2015 at 9:06 PM, Peter Crosthwaite
<address@hidden> wrote:
> On Wed, Sep 30, 2015 at 3:42 PM, Max Filippov <address@hidden> wrote:
>> On Thu, Oct 1, 2015 at 1:23 AM, Peter Crosthwaite
>> <address@hidden> wrote:
>>> On Wed, Sep 30, 2015 at 3:07 PM, Max Filippov <address@hidden> wrote:
>>>> On Thu, Oct 1, 2015 at 12:02 AM, Peter Crosthwaite
>>>> <address@hidden> wrote:
>>>>> Which makes MMU vs noMMU a board level property, not a CPU property.
>>>>> It should appear in QEMU as such.
>>>>
>>>> Ok, one last try: can this property be queried from the selected CPU
>>>> and passed to SoC initialization code?
>>>
>>> No, what I am trying to say is go the other way round. The property is
>>> on the SoC, and it is used to select the CPU type.
>>
>> This is not what happens in reality. In reality the MMU type is the
>> CPU property.
>> A set of CPU properties comes from the outside along with the CPU name, and
>> that's the only possible set of properties for this name.
>> XTFPGA bitstream build scripts lay out its address space based on MMU
>> type of the selected CPU.
>>
>> So let's make XTFPGA an SoC with a property that selects its address space
>> layout. The machine (lx60/lx200/ml605/kc705) is configured with a CPU,
>
> So lx60/lx200 sound like isolated FPGA chips (Virtex 4 lx60?) while
> ml605/kc705 are commonly available fully-featured FPGA dev boards.

Actually they're all fully-featured FPGA dev boards, from different times.
lx60 and lx200 boards were produced by Avnet (yes, Virtex 4 based),
ml605 and kc705 are from Xilinx.

> Is lx60 short for a particular board featuring this part or is it more 
> abstract?

Less memory, smaller onboard FLASH, different audio subsystem (not
currently modeled).

>> it
>> queries MMU type from it and instantiates XTFPGA SoC with proper address
>> space. That seems to be closest to what happens in reality.
>
> What is your intended user command lines? E.g. how do I boot with
> ml605 no-mmu and then with mmu.

'-M ml605 -cpu de108' will boot noMMU variant (de108 is not in the mainline yet,
can be seen in the https://github.com/OSLL/qemu-xtensa/commits/xtensa-cores),
'-M ml605 -cpu dc233c' will boot full MMU variant, as de108 doesn't
have full MMU
and dc233c does.

-- 
Thanks.
-- Max