riscy
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Re: Ethernet stuff

To: riscy@pyramid.com
Subject: Re: Ethernet stuff
From: Drew Eckhardt <drew@hazelrah.cs.Colorado.EDU>
Date: Thu, 08 Jul 1993 02:59:15 -0600
In-reply-to: Your message of "Thu, 08 Jul 1993 09:42:46 +0200." <9307080742.AA14336@resi.waldorf-gmbh.de>
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
    > Depending on how bad the ISA bus interface stuff gets, it might be
    > worth the trouble to just "oem" an ISA card. :-()
    
    Does "oem" mean some sort of reverse engineering or simply to buy them ?

Original Equipment Manufacturer - ie : do what everyone else did, 
and clone National Semi 8390 eval boards... 
    
    > I haven't costed the following out, and it occurs in no particular
    > order, but here goes: a simple on-board 16-bit ethernet would have the
    > following major items (8-bit might save some glue logic and a SRAM,
    > but it would not be a major cost savings, so why no throw it in...)

Getting rid of the SRAM gets messy - the 8390 wants to be a 
busmaster (address space is 64K, although a 32 bit address with static
upper 16 bits can be generated if the two DMA channels are combined 
together), and uses it's busmastering capabilities to handle off-chip
ring buffers.  The SRAM lets the NS sample implementation be a bus
master like it wants, means we don't have to figure out how to get 
it busmastering on our 32 bit bus (the NS 8390 is only 16 bits wide),
and means we don't need to gurantee a 9us DMA latency...
    
    I like to see ethernet on board. People can leave the sockets empty
    if want.

Agreed.  However, how are you going to socket pulse transformers, the 
DC->DC convertor, etc?  IMHO, this is a good argument for propriety
slots on the low speed bus! 

        A large number of users want SCSI, Ethernet.
        
        A few users don't want SCSI, Ethernet, etc.

Leaving empty sockets on some boards will reduce the cost for these
people.  However, sockets still cost money, as does the realestate
lost to the sockets, so it's an imperfect solution.  

        A few users want more Ethernets, more serial ports, etc.

With the current implementation of ethernet on the mainboard, 
serial ports on the mainboard, etc. we have to tell people 
"want more, buy an ISA card" which will probably be more expensive
than what we can do (List price on a dumb BOCA multiport serial
card (16550) is about $250, even at half that it's outrageous).

Having the SCSI, ethernet, serial ports, etc. on daughter cards 
on the propriety bus would keep everybody happy and solve all these
problems.

Also : 

- Bigger circuits (ie, ethernet) eat space on cheaper 2-layer
        boards rather than the expensive mainboard.

- If we use the left rear of the motherboard (adjacent to the ISA
        slots) for the bus, everything is next to a hole in the 
        case and our connector mounting problems disappear.

- Since nobody with one of these cards won't be using the feature,
        we can surface mount things, eliminating the cost of 
        sockets. 
    
    > - 2 8kx8 or 32kx8 SRAM for packet buffering (some controllers use
    >  DRAM, but most use SRAM)

You don't have to refresh DRAM, and for an 8K chip the price difference
won't be that noticeable.

    > - DC_DC converter module
    
    Please correct me if I'm wrong: What other supplies do
    we need than +5, -12 and +12 ? All these come out of
    a standard PC power supply.

15V.

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