LAN9311 Datasheet, PDF (123/461 Pages) SMSC Corporation – Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

TX_FIF_SZ
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Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Datasheet
Table 9.9 Valid TX/RX FIFO Allocations
TX DATA FIFO
SIZE (BYTES)
1536
2560
3584
4608
5632
6656
7680
8704
9728
10752
11776
12800
13824
TX STATUS FIFO
SIZE (BYTES)
512
512
512
512
512
512
512
512
512
512
512
512
512
RX DATA FIFO
SIZE (BYTES)
13440
12480
11520
10560
9600
8640
7680
6720
5760
4800
3840
2880
1920
RX STATUS FIFO
SIZE (BYTES)
896
832
768
704
640
576
512
448
384
320
256
192
128
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 LAN9311/LAN9311i 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 LAN9311/LAN9311i 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.
SMSC LAN9311/LAN9311i
123
DATASHEET
Revision 2.0 (02-14-13)