freebsd-dev/share/man/man4/man4.i386/rdp.4

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.\" Copyright (c) 1997 Joerg Wunsch
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.\" $Id: rdp.4,v 1.1.1.1 1998/12/21 12:43:35 j Exp $
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.\"
.\" " (emacs disconfusion)
.Dd December 21, 1998
.Dt RDP 4 i386
.Os
.Sh NAME
.Nm rdp
.Nd Ethernet driver for RealTek RTL 8002 pocket ethernet
.Sh SYNOPSIS
.Cd "device rdp0 at isa? port 0x378 net irq 7"
.Cd "device rdp0 at isa? port 0x378 net irq 7 flags 0x2"
.Sh DESCRIPTION
The
.Nm
device driver supports RealTek RTL 8002-based pocket ethernet adapters,
connected to a standard parallel port.
.Pp
These adapters seem to belong to the cheaper choices among pocket
ethernet adapters.  The RTL 8002 is the central part, containing an
interface to BNC and UTP (10 Mbit/s) media, as well as a host
interface that is designed to talk to standard parallel printer
adapters.  For the full ethernet adapter to work, it is completed by
an external RAM used as the Tx and Rx packet buffer (16 K x 4 for the
RTL 8002), and an EEPROM to hold the assigned ethernet hardware
address.  For the RTL 8002, the EEPROM can be either a standard 93C46
serial EEPROM (which seems to be a common choice), or a 74S288
parallel one.  The latter variant needs the device configuration flag
0x1 in order to work.
.Pp
Since standard printer adapters seem to vary wildly among their timing
requirements, there are currently two possible choices for the way
data are being exchanged between the pocket ethernet adapter and the
printer interface.  The default is the fastest mode the RTL 8002
supports.  If the printer adapter to use is particularly slow (which
can be noticed by watching the ethernet wire for crippled packets, or
by not seeing correclty received packets), the configuration flag 0x2
can be set in order to throttle down the
.Nm
driver.  Note that in fast mode, the data rate is assymetric, sending
is a little faster (up to two times) than receiving.  Rates like 150
KB/s for sending and 80 KB/s for receiving are common.  For slow mode,
both rates are about the same, and in the range of 50 KB/s through 70
KB/s.  As always, your mileage may vary.
.Pp
In case the adapter isn't recognized at boot-time, setting the
.Em bootverbose
flag
.Pq Ql Fl v
might help in diagnosing the reason.  Since the RTL 8002 requires
the availability of a working interrupt for the printer adapter (unlike
the
.Xr lpt 4
driver), the
.Nm
driver fails to attach if the ethernet adapter cannot assert an
interrupt at probe time.
.Pp
The RTL 8002 doesn't support (hardware) multicast.
.Pp
The
.Nm
driver internally sets a flag so it gets probed very early.  This way,
it is possible to configure both, an
.Nm
driver as well as an
.Xr lpt 4
driver into the same kernel.  If no RTL 8002 hardware is present, probing
will eventually detect the printer driver.
.Sh DIAGNOSTICS
.Pp
.Dl "rdp0: configured IRQ (7) cannot be asserted by device"
.Pp
The probe routine was unable to get the RTL 8002 asserting an interrupt
request through the printer adapter.
.Pp
.Dl "rdp0: failed to find a valid hardware address in EEPROM"
.Pp
Since there doesn't seem to be a standard place for storing the hardware
ethernet address within the EEPROM, the
.Nm
driver walks the entire (serial) EEPROM contents until it finds something
that looks like a valid ethernet hardware address, based on the IEEE's
OUI assignments.  This diagnostic tells the driver was unable to find
one.  Note: it might as well be the current adapter is one of the rare
examples with a 74S288 EEPROM, so
.Ql flags 0x1
should be tried.
.Pp
.Dl "rdp0: Device timeout"
.Pp
After initiating a packet transmission, the ethernet adapter didn't
return a notification of the (successful or failed) transmission.  The
hardware is likely to be wedged, and is being reset.
.Pp
.Sh SEE ALSO
.Xr lpt 4 ,
.Xr ifconfig 8
.Sh AUTHORS
This driver was written by
.ie t J\(:org Wunsch,
.el Joerg Wunsch,
based on RealTek's packet driver for the RTL 8002, as well as on some
description of the successor chip, RTL 8012, RealTek was gratefully
providing.
.Sh BUGS
There are certainly many of them.
.Pp
Since the
.Nm
driver wants to probe its hardware at boot-time, the adapter needs
to be present then in order to be detected.
.Pp
Only two out of the eight different speed modes RealTek's packet
driver could handle are implemented.  Thus there might be hardware
where even the current slow mode is too fast.
.Pp
There should be a DMA transfer test in the probe routine that figures
out the usable mode automatically.
.Pp
Abusing a standard printer interface for data exchange is error-prone.
Occasional stuck hardware shouldn't surprise too much, hopefully the
timeout routine will catch these cases.  Flood-pinging is a good
example of triggering this problem.  Likewise, albeit BPF is of course
supported, it's certainly a bad idea attempting to watch a crowded
ethernet wire using promiscuous mode.
.Pp
Since the RTL 8002 has only 4 KB of Rx buffer space (2 x 2 KB are used
as Tx buffers), the usual NFS deadlock with large packets arriving too
quickly could happen if a machine using the
.Nm
driver NFS-mounts some fast server with the standard NFS blocksize of
8 KB.  (Since NFS can only retransmit entire NFS packets, the same
packet will be retransmitted over and over again.)
.Pp
The heuristic to find out the ethernet hardware address from the
EEPROM sucks, but seems to be the only sensible generic way that
doesn't depend on the actual location in EEPROM.  RealTek's sample
driver placed it directly at address 0, other vendors picked something
like 15, with other junk in front of it that must not be confused with
a valid ethernet address.
.Pp
The driver should support the successor chip RTL 8012, which seems to
be available and used these days.  (The RTL 8002 is already somewhat
aged, around 1992/93.)  The RTL 8012 offers support for advanced
printer adapter hardware, like bidirectional SPP, or EPP, which could
speed up the transfers substantially.  The RTL 8012 also supports
hardware multicast, and has the ability to address 64 K x 4 packet
buffer RAM.
.Pp
The driver should be layered upon the ppc driver, instead of working
standalone, and should be available as a loadable module, so the
device probing can be deferred until the pocket ethernet adapter has
actually been attached.