
	TRW PC 2000 Ethernet Driver For MIT-CMU PC/IP.

The files in this directory are a driver for the TRW PC 2000 Ethernet
board for IBM PC and PC/AT class machines.  The driver supports all
of the normal PC/IP applications, including "netwatch".

The PC 2000 board is a high performance Ethernet adaptor.  Its
features include:
	-  Intel 82586 LAN controller.
	-  128K or 256K of on-board memory.
	-  Standard AUI (15 pin) and Cheapernet net interfaces.
	-  8 and 16 bit wide buss interface.
	-  Board memory accessible through a memory window or through
	   I/O ports (8 or 16 bit wide) with auto-incrementing memory
	   addresses.
	-  Optional Intel 80186 on-board processor.

The board and driver are well suited to heavy traffic conditions with
closely spaced packets.  For most applications, the on-board buffers
can hold up to 73 full-sized received packets.  For netwatch, the
number of packets awaiting software processing can exceed 1100.
(This is in addition to netwatch's own 512 packet buffers.)

Since the 82586 can send packets with nearly the minimum legal
interframe spacing, use of chaining could swamp other machines with
slower interfaces.  To avoid this problem, the driver avoids use of
the 82586's transmit chaining capability.

The driver uses 128K of board memory.  Board memory access is by I/O
ports.  The board memory is never mapped into PC memory to avoid
potential conflicts with other hardware (in particular EGA display
controllers or EMS memory.)

The driver is intended to be compiled using the following tools:
	Polytron PVCS (optional)
	Polytron Polymake (other "makes" may be used with appropriate
			   revisions of the makefile.)
        Microsoft Macro Assembler version 4, 5, or 5.1.
	Microsoft C, version 5.

There is one particularly unusual characteristic of the driver worthy
of special mention: Each time the driver starts, it performs a time
domain reflectometer (TDR) check on the network.  This has not yet
been found to cause any problems -- typically other nodes perceive
the TDR signal as a mal-formed error packet.  However, on broadband
networks, the TDR function sometimes indicates a failure when none
really exists.  To override the TDR check, the driver uses the
transmit DMA value in the customized configuration.  (The driver does
not use DMA, so the transmit DMA setting is otherwise unused.)  If
the transmit DMA is set to zero, the TDR check will be performed.  If
set to non-zero, the TDR check will be bypassed.
