91C94 Datasheet, PDF (68/120 Pages) SMSC Corporation – ISA/PCMCIA SINGLE CHIP ETHERNET CONTROLLER WITH RAM

TYPICAL FLOW OF EVENTS FOR RECEIVE
S/W DRIVER
CSMA/CD SIDE
1 ENABLE RECEPTION - By setting the RXEN
bit.
2
A packet is received with matching address.
Memory is requested from MMU. A packet
number is assigned to it. Additional memory
is requested if more pages are needed.
3
The internal DMA logic generates sequential
addresses and writes the receive words into
memory. The MMU does the sequential to
physical address translation. If overrun,
packet is dropped and memory is released.
4
When the end of packet is detected, the status
word is placed at the beginning of the receive
packet in memory. Byte count is placed at the
second word. If the CRC checks correctly the
packet number is written into the RX FIFO.
The RX FIFO being not empty causes RCV
INT (interrupt) to be set. If CRC is incorrect
the packet memory is released and no
interrupt will occur.
5 SERVICE INTERRUPT - Read the Interrupt
Status Register and determine if RCV INT is
set. The next receive packet is at receive area.
(Its packet number can be read from the FIFO
Ports Register). The software driver can
process the packet by accessing the RX area,
and can move it out to system memory if
desired. When processing is complete the
CPU issues the REMOVE AND RELEASE
FROM TOP OF RX command to have the
MMU free up the used memory and packet
number.
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