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from: @(#)ec.4 8.1 (Berkeley) 6/5/93
.Dd February 5, 2019 .Dt EC 4 vax .Os .Sh NAME .Nm ec .Nd 3Com 10 Mb/s Ethernet interface .Sh SYNOPSIS .Cd "ec0 at uba0 csr 161000 vector ecrint eccollide ecxint flags 0" .Sh DESCRIPTION NOTE: This driver has not been ported from x 4.4 yet.
p The .Nm ec interface provides access to a 10 Mb/s Ethernet network through a 3Com controller.
p The hardware has 32 kilobytes of dual-ported memory on the .Tn UNIBUS . This memory is used for internal buffering by the board, and the interface code reads the buffer contents directly through the .Tn UNIBUS . The address of this memory is given in the .Ar flags field in the configuration file. The first interface normally has its memory at UNIBUS address 0.
p Each of the host's network addresses is specified at boot time with an .Dv SIOCSIFADDR .Xr ioctl 2 . The .Nm ec interface employs the address resolution protocol described in .Xr arp 4 to dynamically map between Internet and Ethernet addresses on the local network.
p The interface software implements an exponential backoff algorithm when notified of a collision on the cable. This algorithm uses a 16-bit mask and the .Tn VAX-11 Ns 's interval timer in calculating a series of random backoff values. The algorithm is as follows: l -enum -offset indent t Initialize the mask to be all 1's. t If the mask is zero, 16 retries have been made and we give up. t Shift the mask left one bit and formulate a backoff by masking the interval timer with the smaller of the complement of this mask and a 5-bit mask, resulting in a pseudo-random number between 0 and 31. This produces the number of slot times to delay, where a slot is 51 microseconds. t Use the value calculated in step 3 to delay before retransmitting the packet. The delay is done in a software busy loop. .El .Sh DIAGNOSTICS l -diag t ec%d: send error. After 16 retransmissions using the exponential backoff algorithm described above, the packet was dropped. t ec%d: input error (offset=%d). The hardware indicated an error in reading a packet off the cable or an illegally sized packet. The buffer offset value is printed for debugging purposes. t ec%d: can't handle af%d. The interface was handed a message with addresses formatted in an unsuitable address family; the packet was dropped. .El .Sh SEE ALSO .Xr arp 4 , .Xr inet 4 , .Xr netintro 4 .Sh HISTORY The .Nm driver appeared in x 4.2 . .Sh BUGS The hardware is not capable of talking to itself. The software implements local sending and broadcast by sending such packets to the loop interface. This is a kludge.
p Backoff delays are done in a software busy loop. This can degrade the system if the network experiences frequent collisions.
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