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List:       freebsd-hackers
Subject:    Re: diskless hardware *design* suggestions
From:       Don Yuniskis <dgy () rtd ! com>
Date:       1997-05-31 21:13:56
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It seems that Michael Smith said:
> Don Yuniskis stands accused of saying:
> >     I'm hacking together an SC400 (486/66 PC on a chip) based design
> > and would like that design to serve double duty as the core of an
> > FBSD-based diskless system (e.g., a small X-terminal).
> 
> Hey, neat.  What VGA CRTC were you planning on using?

Haven't yet decided since that would be a daughterboard,
anyway.  BTW, the SC400 includes support for direct drive
of an LCD display, etc.  It *could* be kludged to drive
a CRT with a small effort...

> >     Unfortunately, none of the x86 MCU's are particularly
> > tolerant of external bus masters.  And, sharing memory tends to
> > clutter these designs quickly.  So, DMA is the only *painless*
> > way to interface to the core.
> 
> DMA is not common with NICs.  Shared memory (usually controlled by 
> the NIC) and programmed I/O are the norm.

Yes.  Those NIC's that support DMA tend to be bus-mastering
themselves -- hence my problem!

> >     As such, are there any good suggestions for NIC's that would
> > fit well in this architecture?  Preferably fast ethernet?  Very
> > high integration is desirable to keep the size of the box down to
> > a minimum (i.e. PC/104 form factor).
> 
> There aren't a great number of fast ethernet chipsets, and even fewer
> designed for tight ISA-style integration.  There is, however, a
> plethora of 10Mbps chipsets that might suit; consider the Crystal
> CS89x0, SMC 91cxx, NatSemi 83c90x etc.
> 
> Depending on the actual situation, you may find that the AMD PC-Net or
> Intel 825xx parts are suitable too. would strongly suggest chasing the
> SMC and NatSemi websites for details on any potential 100Mbps parts.

AMD's devices that are interesting all want to be bus masters.
Some of SMC's newer parts are somewhat appealing (10Base*
devices with integrated RAM, etc.).  Still no clear cut "winners",
though...  it's unfortunate that all the [34]86 MCU's have either
missing DRAM controllers or poor/nonexistent support for
bus mastering (obviously because they would have to drive the bus
back *into* the MCU core...)

thx!
--don

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