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EN/SC (was: NetBSD 8.0 on a Mac LC III)

On Oct 10, 2018, at 2:16 PM, David Riley <david%the-rileys.net@localhost> wrote:
>> I have an Asante EN/SC and could help with testing of that, too,
>> though I'm not aware of any drivers for it (Linux or NetBSD).  And
>> the lack of documentation would likely be a problem.
> Mostly I'm interested in seeing what's inside. If you've the inclination to take it apart and photograph the innards, that would be a help; the rest of it, I was going to reverse engineer from the Mac driver, because I have a copy of MacNosyII and know what to do with it. :-)  If the innards contain some reasonably standard processor, I'd love to be able to dump the firmware for reverse engineering as well (I also have a copy of IDA Pro).

OK, I actually ended up acquiring one from a friend who lives nearby. Opening it up, it looks like it doesn't have a CPU at all; it's a few GALs, some 74xxx buffers and registers, a DP83902 ("ST-NIC", pretty common on Mac Ethernet cards) Ethernet controller, 32K of RAM and a 27C256 EPROM.  Most likely, the EPROM drives a state machine controlled through the registers and the GALs to wrap the DP83902 interface (and, probably, the RAM) in a SCSI veneer.

That explains the performance; the data transfer speed is probably reasonable in the data blocks, but the register accesses have got to be punishing (SCSI doesn't provide for particularly speedy transaction turnaround times because it's meant to give the slowest devices time to respond).

In any case, I'd still be interested in working on an EN/SC driver assuming it's not unreasonable to wrap an existing DP83902 driver around SCSI accesses in NetBSD.  But if I'm developing something new to provide Ethernet access to older machines, it probably makes more sense to start with a higher level control strategy to minimize the transactions, so backwards compatibility doesn't really make sense here.  Plus, I'd be insane to try to directly replicate the register set of the DP83902 just for compatibility with older drivers.

- Dave

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