lan91c100 Standard Microsystems Corp., lan91c100 Datasheet - Page 65

• Manufacturer Part Number: lan91c100
• Description: Feast ? Ast Ethernet Controller
• Manufacturer: Standard Microsystems Corp.

AUTO RELEASE - When set, successful
transmit packets are not written into completion
FIFO,
automatically.
1)
set AUTO RELEASE=0.
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.
LAN91C100 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 DONE PACKET
NUMBER at the FIFO PORTS register.
eliminates the need for the driver to keep a list
of packet numbers being transmitted.
numbers are queued by the LAN91C100 and
provided back to the CPU as their transmission
completes.
2)
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.
One interrupt per packet: enable TX INT,
One interrupt per sequence of packets:
and
their
memory
The software driver
is
released
This
The
The
65
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 LAN91C100 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)
2)
3)
1) and 3) also share the usage of the Packet
Number
restoring the PNR is also required from interrupt
service routines.
Transmit
driven)
Receive unloading (interrupt driven)
Transmit Status reading (interrupt driven).
Register.
loading
Therefore
(sometimes
saving
interrupt
and