On 29 September 2015 at 11:34, Max Filippov <jcmvb...@gmail.com> wrote: > On Mon, Sep 28, 2015 at 12:59 AM, Peter Crosthwaite > <crosthwaitepe...@gmail.com> wrote: >> On Sun, Sep 27, 2015 at 2:48 PM, Max Filippov <jcmvb...@gmail.com> wrote: >>> On Mon, Sep 28, 2015 at 12:28 AM, Peter Crosthwaite >>> <crosthwaitepe...@gmail.com> 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.
I think this should clearly be different machine models (possibly implemented using different SoC models). This isn't a CPU-dependent thing at all, it's just your dev tools are hiding "change the devices and other board/soc level things" behind a CPU-type dropdown, which it can get away with because the whole implementation is in a single FPGA. Compare vexpress-a9 vs vexpress-a15 (which are modelling hardware with a daughterboard with CPU and devices on it, which is sort of analogous I think). thanks -- PMM
