IBM PowerPC 405GP User Manual page 567

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