On Thu, Sep 15, 2011 at 09:45:33PM +0100, Peter Maydell wrote:
> On 15 September 2011 21:29, Gleb Natapov <g...@redhat.com> wrote:
> > 16650A is not a device. ISA card it resides on is a device.
>
> The 16550A is an encapsulated set of functionality with some
> well defined interfaces ("I provide a set of memory mapped
> registers", "I have an output gpio line (irq)"), which we
> need to be able to compose into other things (lots of models
> use a 16550A one way or another, not just the ISA serial card),
> connect up (ie connect that irq to an appropriate interrupt
> controller, map the registers in system memory or under ISA
> or whatever), and configure (eg specify the backend chardev).
>
> I don't think there's any difference at all between that
> and (say) the NE2000 PCI model, which also is encapsulated
> functionality with well defined interfaces that we need to
> be able to compose and connect and configure. We should be
> using the same implementation and abstractions for both
> cases.
>
IDE is another such device (it was ISA later converted to PCI).
As far as I understand your view of UART is the same as mine.
It is not a whole device, but only a part of it.
> (Note the analogy to hardware: a 16550A chip is a well
> specified encapsulated set of functionality with some
> electrical, timing, etc restrictions on its use. The
> only difference between that and an ISA card is that the
> ISA card happens to be physically manufactured so that an
> end user can plug it, unplug it and wave it around.)
>
> -- PMM
--
Gleb.
