[Coco] Fwd: IP packets on my coco

[John W. Linville]

On Thu, Jun 09, 2016 at 08:19:43PM -0500, RETRO Innovations wrote:
> On 6/9/2016 12:36 PM, John W. Linville wrote:
> > https://www.cirrus.com/jp/pubs/proDatasheet/CS8900A_F5.pdf
> > 
> >  From page 77:
> > 
> > 4.10.9  Basic I/O Mode Receive
> > 
> > I/O Mode receive operations occur in the following order (In this
> > example, interrupts are enabled to signal the presence of a valid
> > receive frame):
> > 
> > 1)  A frame is received by the CS8900A, triggering an enabled
> > interrupt.
> > 
> > <snip>
> > 
> > That looks fairly clear to me.  Is the datasheet wrong?
> I don't think it is wrong, but maybe it is incomplete.  Numerous developers
> in the 64 side have lamented the lack of IRQ capability in IO mode.  I will
> check to see where they got their information.

Well, it looks like the datasheet might be wrong...

Application Note 181 from Cirrus Logic says:

"Unsupported functions in 8 bit mode

- Interrupts are not supported. Polled mode must
  be used.

- The DMA engine only uses 16 bit memory ac-
  cesses and does not support 8 bit transfers.

- The packet page pointer has an auto increment
  feature that cannot be used in 8 bit mode.

- An EEPROM is not supported.  Most 8 bit de-
  signs should not require one and can eliminate
  the added cost."

And Application note 205 says:

"1) Application Note 181 says that interrupts are not supported
in 8-bit mode. Is this really true?

Yes, interrupts are NOT supported in 8-bit mode. They might appear
to work for a while but will eventually fail."

So apparently the 8-bit mode is a bit unreliable in the CS8900A?

With that said, the usefulness of interrupts for servicing an Ethernet
NIC on <2MHz CPU is debatable...

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.