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LAN91C110

FEAST Fast Ethernet Controller for PCMCIA and Generic 16-Bit Applications

SMSC -> Microchip 

FEAST Fast Ethernet Controller for PCMCIA and Generic 16-Bit Applications

Datasheet

1. One interrupt per packet: enable TX INT, set AUTO RELEASE=0. The software driver can find the

completion result in memory and process the interrupt one packet at a time. Depending on the

completion code the driver will take different actions. Note that the transmit process is working in

parallel and other transmissions might be taking place. The LAN91C110 is virtually queuing the

packet numbers and their status words.

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

reading the TX FIFO 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 LAN91C110

and provided back to the CPU as their transmission completes.

2. 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 LAN91C110 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:

1. Transmit loading (sometimes interrupt driven)

2. Receive unloading (interrupt driven)

3. 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.

SMSC LAN91C110 Rev. B

Page 47

DATASHEET

Revision 1.0 (11-04-08)

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