High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
Table 9.9 Valid TX/RX FIFO Allocations
TX DATA FIFO
SIZE (BYTES)
TX STATUS FIFO
SIZE (BYTES)
RX DATA FIFO
SIZE (BYTES)
RX STATUS FIFO
SIZE (BYTES)
TX_FIF_SZ
2
3
1536
2560
3584
4608
5632
6656
7680
8704
9728
10752
11776
12800
13824
512
512
512
512
512
512
512
512
512
512
512
512
512
13440
12480
11520
10560
9600
8640
7680
6720
5760
4800
3840
2880
1920
896
832
768
704
640
576
512
448
384
320
256
192
128
4
5
6
7
8
9
10
11
12
13
14
9.8
TX Data Path Operation
Data is queued for transmission by writing it into the TX Data FIFO. Each packet to be transmitted
may be divided among multiple buffers. Each buffer starts with a two DWORD TX command (TX
command ‘A’ and TX command ‘B’). The TX command instructs the LAN9312 on the handling of the
associated buffer. Packet boundaries are delineated using control bits within the TX command.
The host provides a 16-bit Packet Tag field in the TX command. The Packet Tag value is appended
to the corresponding TX status DWORD. All Packet Tag fields must have the same value for all buffers
in a given packet. If tags differ between buffers in the same packet the TXE error will be asserted. Any
value may be chosen for a Packet Tag as long as all tags in the same Packet are identical. Packet
Tags also provide a method of synchronization between transmitted packets and their associated
status. Software can use unique Packet Tags to assist with validating matching status completions.
Note: The use of Packet Tags is not required by the hardware. This field can be used by the LAN
software driver for any application. Packet Tags is only one application example.
The Packet Length field in the TX command specifies the number of bytes in the associated packet.
All Packet Length fields must have the same value for all buffers in a given packet. Hardware
compares the Packet Length field and the actual amount of data received by the Ethernet controller.
If the actual packet length count does not match the Packet Length field as defined in the TX
command, the Transmitter Error (TXE) flag is asserted.
The LAN9312 can be programmed to start payload transmission of a buffer on a byte boundary by
setting the “Data Start Offset” field in the TX command. The “Data Start Offset” field points to the actual
start of the payload data within the first 8 DWORDs of the buffer. Data before the “Data Start Offset”
pointer will be ignored. When a packet is split into multiple buffers, each successive buffer may begin
on any arbitrary byte.
Revision 1.2 (04-08-08)
122
SMSC LAN9312
DATASHEET
SMSC [ SMSC CORPORATION ]
