Datasheet

____________________________________________________ DS34S101, DS34S102, DS34S104, DS34S108
Rev: 032609 77 of 198
10.6.11.13 CPU to Ethernet Flow
The Tx Ethernet interface polls the CPU-to-Ethernet queue for new packets waiting in the SDRAM to be processed.
If the queue level is greater than zero and no buffers from the payload-type machines are waiting in the Ethernet Tx
queue, the Tx Ethernet interface extracts the pointer and copies the relevant data from the SDRAM buffer to the
Ethernet MAC block. It then checks whether the CPU TX return queue is not full to return the pointer. If the return
queue is full, it keeps the pointer and does not poll the CPU-to-ETH queue until it succeeds in returning the pointer.
After returning the pointer to the CPU TX return queue for reuse, the Tx Ethernet interface is ready to take another
pointer from the CPU-to-ETH queue.
The CPU-to-Ethernet queue and the CPU Tx return queue can contain up to 32 pointers each. Section 11.4.6
describes the pool and queue registers.
Figure 10-56. CPU-to-Ethernet Flow
CPU TO ETH
QUEUE
CPU TX
RETURN
QUEUE
SDRAM
ETH MAC
LOOP CLOSED BY THE CPU
TX ETH
INTERFACE
TDMoP Block