[ECOS] Re: Port of 82559 ethernet driver for PC target (was: "RE: [ECOS] New bie Question!")

[Andrew Lunn <andrew.lunn@ascom.ch>]

> > Decide where to put the PCI memory window. Change the MMU to support
> > this. Also watch out for the new heap/malloc code. It may try to put a
> > heap on the PCI window. 
> 
> Well, Afaik there is no MMU involved in the 386-PC target. It uses a simple
> 32 bits flat model.
> 
> So I don't think there is no need to setup a PCI memory window. I think the
> 3 BAR are setup by the BIOS. I read:

Well, on the EBSA you have to tell the MMU not to use the read cache
or the write buffer for the memory in the PCI window. I presume the
same applies for the 386-PC?
 
> And for the heap/malloc things, I don't understand why there is a special
> malloc stuff. Why not regular memory pools?. And it seems there is need to
> set up a region in the memory layout. Why?

You need some memory for receive and transmit bufferes. These go into
the PCI window. On the EBSA you can only fiddle the cache for 1Mbyte
pages so 1Mbytes has been allocated to the PCI window. This is in real
RAM. I think to stop the new heap code trying to use this piece of
memory a section is placed on top of it. I've not looked at the
details, i just know it works somehow. Maybe Hugo or Jifl can
clarrify?
 
> As I understand how the 82559 works, when we want to send a packet, we have
> to write the adress of some structure in the SCB General Pointer register
> (offset 04h) and then a transmit command in the SCB command register. Is
> that right? If so, the adress we pass can just be anywhere in memory right?

It has to be in the PCI window and somewhere the DMA can get it. I
know in olden days the i386 hardware was limmited on where the DMA
could work. Does this apply? Its a long time since i've played with
this sort of thing.

        Andrew