NAME

le — AMD 7990, 79C90, 79C960, 79C970 LANCE Ethernet interface driver

SYNOPSIS

DESCRIPTION

The le interface provides access to a Ethernet network via the AMD Am7990 and Am79C90 (CMOS, pin-compatible) LANCE (Local Area Network Controller - Ethernet) chip set.

The le driver also supports PCnet-PCI cards based on the AMD 79c970 chipset, which is a single-chip implementation of a LANCE chip and PCI bus interface.

Each of the host's network addresses is specified at boot time with an SIOCSIFADDR ioctl(2). The le interface employs the Address Resolution Protocol (ARP) described in arp(4) to dynamically map between Internet and Ethernet addresses on the local network.

Selective reception of multicast Ethernet frames is provided by a 64-bit mask; multicast destination addresses are hashed to a bit entry using the Ethernet CRC function.

The use of “trailer” encapsulation to minimize copying data on input and output is supported by the interface but offers no advantage on systems with large page sizes. The use of trailers is automatically negotiated with ARP. This negotiation may be disabled, on a per-interface basis, with ifconfig(8).

HARDWARE

DIAGNOSTICS

le%d: overflow

More packets came in from the Ethernet than there was space in the receive buffers. Packets were missed.

le%d: receive buffer error

Ran out of buffer space, packet dropped.

le%d: lost carrier

The Ethernet carrier disappeared during an attempt to transmit. It will finish transmitting the current packet, but will not automatically retry transmission if there is a collision.

le%d: excessive collisions, tdr %d

Ethernet extremely busy or jammed, outbound packets dropped after 16 attempts to retransmit.

TDR is “Time Domain Reflectometry”. The LANCE TDR value is an internal counter of the interval between the start of a transmission and the occurrence of a collision. This value can be used to determine the distance from the Ethernet tap to the point on the Ethernet cable that is shorted or open (unterminated).

le%d: dropping chained buffer

Packet didn't fit into a single receive buffer, packet dropped. Since the le driver allocates buffers large enough to receive the maximum size Ethernet packet, this means some other station on the LAN transmitted a packet larger than allowed by the Ethernet standard.

le%d: transmit buffer error

LANCE ran out of buffer before finishing the transmission of a packet. If this error occurs, the driver software has a bug.

le%d: underflow

LANCE ran out of buffer before finishing the transmission of a packet. If this error occurs, the driver software has a bug.

le%d: controller failed to initialize

Driver failed to start the AM7990 LANCE. This is potentially a hardware failure.

le%d: memory error

RAM failed to respond within the timeout when the LANCE wanted to read or write it. This is potentially a hardware failure.

le%d: receiver disabled

The LANCE receiver was turned off due to an error.

le%d: transmitter disabled

The LANCE transmitter was turned off due to an error.

SEE ALSO

arp(4), ifmedia(4), inet(4), intro(4), mca(4), ifconfig(8)

Am79C90 - CMOS Local Area Network Controller for Ethernet, 17881, May 1994, Advanced Micro Devices.

HISTORY

The pmax le driver is derived from a le driver that first appeared in 4.4BSD. Support for multiple bus attachments first appeared in NetBSD 1.2.

The Amiga le interface first appeared in NetBSD 1.0

The Ariadne Ethernet card first appeared with the Amiga ae interface in NetBSD 1.1 and was converted to the Amiga le interface in NetBSD 1.3

BUGS

The Am7990 Revision C chips have a bug which causes garbage to be inserted in front of the received packet occasionally. The work-around is to ignore packets with an invalid destination address (garbage will usually not match), by double-checking the destination address of every packet in the driver. This work-around is enabled with the LANCE_REVC_BUG kernel option.

When LANCE_REVC_BUG is enabled, the le driver executes one or two calls to an inline Ethernet address comparison function for every received packet. On the mc68000 it is exactly eight instructions of 16 bits each. There is one comparison for each unicast packet, and two comparisons for each broadcast packet.

In summary, the cost of the LANCE_REVC_BUG option is:

1. loss of multicast support, and
2. eight extra CPU instructions per received packet, sometimes sixteen, depending on both the processor, and the type of packet.

All sun3 systems are presumed to have this bad revision of the Am7990, until proven otherwise. Alas, the only way to prove what revision of the chip is in a particular system is inspection of the date code on the chip package, to compare against a list of what chip revisions were fabricated between which dates.

Alas, the Am7990 chip is so old that AMD has “de-archived” the production information about it; pending a search elsewhere, we don't know how to identify the revision C chip from the date codes.

On all pmax front-ends, performance is impaired by hardware which forces a software copy of packets to and from DMA buffers. The ioasic machines and the DECstation 3100 must copy packets to and from non-contiguous DMA buffers. The DECstation 5000/200 and the PMAD-AA must copy to and from an onboard SRAM DMA buffer. The CPU overhead is noticeable, but all machines can sustain full 10 Mb/s media speed.