Re: [Qemu-devel] [PATCH v3 1/1] nios2: Add Altera JTAG UART emulation

[Bystricky, Juro]

> >> [...]
> >>
> >>>>> +static uint64_t altera_juart_read(void *opaque, hwaddr addr,
> unsigned
> >>>> int size)
> >>>>> +{
> >>>>> +    AlteraJUARTState *s = opaque;
> >>>>> +    uint32_t r;
> >>>>> +
> >>>>> +    addr >>= 2;
> >>>>
> >>>> Hmmmmm, how will unaligned read from one of these registers be handled
> >>>> on real HW ? ie. read from address 0x3 ? What about writes ?
> >>>>
> >>>
> >>> there is no reading/writing going on via "addr".
> >>> This just maps the hw address into register number, where registers are
> >> at
> >>> 4 bytes boundaries (so they are aligned as needed) but indexed as
> >> 1,2,3....
> >>> (Pretty common code in other drivers.)
> >>> But will redo the code anyway so there are no shifts.
> >>
> >> This doesn't answer my question at all. How does real hardware behave if
> >> you read from unaligned address in the register space , ie. offset 0x3 ?
> >>
> >
> > Not sure I understand the question here. Which "real hardware" are we
> talking about?
> 
> By real hardware I mean real Nios2 system ...
> 
> > If "real hardware" contains MMU or MPU then an exception is generated on
> misalign access.
> 
> Is this handled here or not ?
> 

Sorry, I am not sure I understand the question.
Exceptions are handled by interrupt controller.
This code for JTAG UART does not have any misaligned accesses.