LAN91C100FD datasheet(51/79 Pages) SMSC

51 / 79 page

FEAST Fast Ethernet Controller with Full Duplex Capability

SMSC DS – LAN91C100FD Rev. D

Page 51

Rev. 10/14/2002

PRELIMINARY

In this case, the transmit interrupt service routine can find the next packet number to be serviced by

reading the TX DONE PACKET NUMBER at the FIFO PORTS register. This eliminates the need for the

driver to keep a list of packet numbers being transmitted. The numbers are queued by the LAN91C100FD

and provided back to the CPU as their transmission completes.

One interrupt per sequence of packets: Enable TX EMPTY INT and TX INT, set AUTO RELEASE=1.

TX EMPTY INT is generated only after transmitting the last packet in the FIFO.

TX INT will be set on a fatal transmit error allowing the CPU to know that the transmit process has

stopped and therefore the FIFO will not be emptied.

This mode has the advantage of a smaller CPU overhead, and faster memory de-allocation. Note that

when AUTO RELEASE=1 the CPU is not provided with the packet numbers that completed

successfully.

Note:

The pointer register is shared by any process accessing the LAN91C100FD memory. In order to allow

processes to be interruptable, the interrupting process is responsible for reading the pointer value before

modifying it, saving it, and restoring it before returning from the interrupt.

Typically there would be three processes using the pointer:

Transmit loading (sometimes interrupt driven)

Receive unloading (interrupt driven)

Transmit Status reading (interrupt driven).

1) and 3) also share the usage of the Packet Number Register. Therefore saving and restoring the PNR is

also required from interrupt service routines.

LAN91C100FD Datasheet(PDF) 51 Page - SMSC Corporation