LAN9117 Datasheet, PDF (46/114 Pages) SMSC Corporation – HIGH PERFORMANCE SINGLE-CHIP 10/100 NON-PCI ETHERNET CONTROLLER

LAN9117
3.13.7 TRANSMITTER ERRORS
If the Transmitter Error (TXE) flag is asserted for any reason, the transmitter will continue operation. TX Error (TXE) will
be asserted under the following conditions:
• If the actual packet length count does not match the Packet Length field as defined in the TX command.
• Both TX command ‘A’ and TX command ‘B’ are required for each buffer in a given packet. TX command ‘B’ must
be identical for every buffer in a given packet. If the TX command ‘B’ words do not match, the Ethernet controller
will assert the Transmitter Error (TXE) flag.
• Host overrun of the TX data FIFO.
• Overrun of the TX status FIFO (unless TXSAO is enabled)
3.13.8 STOPPING AND STARTING THE TRANSMITTER
To halt the transmitter, the host must set the TX_STOP bit in the TX_CFG register. The transmitter will finish sending
the current frame (if there is a frame transmission in progress). When the transmitter has received the TX status for this
frame, it will clear the TX_STOP and TX_ON bits, and will pulse the TXSTOP_INT.
Once stopped, the host can optionally clear the TX status and TX data FIFOs. The host must re-enable the transmitter
by setting the TX_ON bit. If the there are frames pending in the TX data FIFO (i.e., TX data FIFO was not purged), the
transmission will resume with this data.
3.14 RX Data Path Operation
When an Ethernet Packet is received, the MIL first begins to transfer the RX data. This data is loaded into the RX data
FIFO. The RX data FIFO pointers are updated as data is written into the FIFO.
The last transfer from the MIL is the RX status word. The LAN9117 implements a separate FIFO for the RX status words.
The total available RX data and status queued in the RX FIFO can be read from the RX_FIFO_INF register. The host
may read any number of available RX status words before reading the RX data FIFO.
The host must use caution when reading the RX data and status. The host must never read more data than what is
available in the FIFOs. If this is attempted an underrun condition will occur. If this error occurs, the Ethernet controller
will assert the Receiver Error (RXE) interrupt. If an underrun condition occurs, a soft reset is required to regain host
synchronization.
A configurable beginning offset is supported in the LAN9117. The RX data Offset field in the RX_CFG register controls
the number of bytes that the beginning of the RX data buffer is shifted. The host can set an offset from 0-31 bytes. The
offset may be changed in between RX packets, but it must not be changed during an RX packet read.
The LAN9117 can be programmed to add padding at the end of a receive packet in the event that the end of the packet
does not align with the host burst boundary. This feature is necessary when the LAN9117 is operating in a system that
always performs multi-DWORD bursts. In such cases the LAN9117 must ensure that it can transfer data in multiples of
the Burst length regardless of the actual packet length. When configured to do so, the LAN9117 will add extra data at
the end of the packet to allow the host to perform the necessary number of reads so that the Burst length is not cut short.
Once a packet has been padded by the H/W, it is the responsibility of the host to interrogate the Packet length field in
the RX status and determine how much padding to discard at the end of the Packet.
It is possible to read multiple packets out of the RX data FIFO in one continuous stream. It should be noted that the
programmed Offset and Padding will be added to each individual packet in the stream, since packet boundaries are
maintained.
3.14.1 RX SLAVE PIO OPERATION
Using PIO mode, the host can either implement a polling or interrupt scheme to empty the received packet out of the
RX data FIFO. The host will remain in the idle state until it receives an indication (interrupt or polling) that data is avail-
able in the RX data FIFO. The host will then read the RX status FIFO to get the packet status, which will contain the
packet length and any other status information. The host should perform the proper number of reads, as indicated by
the packet length plus the start offset and the amount of optional padding added to the end of the frame, from the RX
data FIFO.
DS00002267A-page 46
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