Figure 20-4 describes the software and hardware operations when receiving a typical packet.
Protocol Stack
Packet
t
11
The numbered steps are described as follows:
1. Software device driver initializes the receive buffer descriptors.
2. Software device driver
enables the
eOMMAe
to process a new packet.
3. A packet is received from the network (steps 2 and 3 can change
in
order).
4. The
eOMMAe
channel requests that MAL process a new packet.
5.
MAL fetches receive buffer information from the descriptor table.
6.
MAL writes the control word from the descriptor to the
eOMMAe
and initiates the data
transfer.
7.
The
eOMMAe
channel fills its FIFO storage.
8.
MAL stores the packet
in
system memory buffers pointed to
by
the descriptors.
9.
MAL reads status information from the
eOMMAe
and writes it to the buffer descriptors.
10. Software device driver is interrupted (if interrupt conditions are met) by the
eOMMAe
or
by the MAL end-of-buffer interrupt.
11
. The receive packet is passed to the protocol stack.
12. Software
clears the receive buffer descriptor positions allowing them to be used again.
Figure
20-4. Receive
Operation
Note: The description
in
Figure 20-4 is the general scheme for MAL operation
in
the software
environment. The device driver
should follow recommendations from "MAL Programming
Notes" on page
20-18.
20-6
PPC405GP
User's Manual Preliminary
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