On Mon, Sep 28, 2015 at 12:28 AM, Peter Crosthwaite <crosthwaitepe...@gmail.com> wrote: > On Sun, Sep 27, 2015 at 12:01 PM, Max Filippov <jcmvb...@gmail.com> wrote: >> On Sun, Sep 27, 2015 at 9:43 PM, Peter Crosthwaite >> <crosthwaitepe...@gmail.com> wrote: >>> On Sun, Sep 27, 2015 at 11:13 AM, Max Filippov <jcmvb...@gmail.com> wrote: >>>> On Sun, Sep 27, 2015 at 8:38 PM, Peter Crosthwaite >>>>>> + mmu = xtensa_option_enabled(env->config, XTENSA_OPTION_MMU); >>>>> >>>>> This looks backwards, the board should be in charge of itself and the >>>>> CPU config, rather than spying on the CPU setup to rewire the board. >>>> >>>> Well, it's an FPGA board and all connections are a part of bitstream. >>>> It's generated that way, I'm just following the specification here. >>>> >>> >>> OK, but the xtensa-CPU is not the bitstream, this board is. What >>> exactly is the user interface for switching between MMU and no-MMU? >> >> Actually they both are. The user interface is a dropbox in the processor >> generator software where user chooses memory management option. >> Once it (and a bunch of other parameters) is chosen the bitstream with >> CPU and peripherals can be generated. >> >>> With the major changes of address layout, the no-MMU variation should >>> be a set of new boards or a machine level parameterisation (i.e. QOM >>> property of the machine). It needs to be user-visible as different on >>> the machine level. >> >> Why? The layouts are hard-coded based on MMU presence anyway. > > So this really means that MMUness is board level property, not a CPU > level property.
CPU is primary, because one can generate RTL for CPU only. If a whole FPGA bitstream is generated, address space layout will be chosen in accordance with MMU presence in CPU. > 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. There are no noMMU cores in the QEMU mainline ATM, but there are cpu3400, dsp3400, lx106 and de108 in the xtensa-cores branch of my tree ( https://github.com/OSLL/qemu-xtensa/commits/xtensa-cores ). -- Thanks. -- Max
