LAN9211_12 Datasheet, PDF (89/147 Pages) SMSC Corporation – High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX Support

High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX Support
Datasheet
5.3.9.1
Allowable settings for Configurable FIFO Memory Allocation
TX and RX FIFO space is configurable through the CSR - HW_CFG register defined above. The user
must select the FIFO allocation by setting the TX FIFO Size (TX_FIF_SZ) field in the hardware
configuration (HW_CFG) register. The TX_FIF_SZ field selects the total allocation for the TX data path,
including the TX Status FIFO size. The TX Status FIFO size is fixed at 512 Bytes (128 TX Status
DWORDs). The TX Status FIFO length is subtracted from the total TX FIFO size with the remainder
being the TX data FIFO Size. Note that TX data FIFO space includes both commands and payload
data.
RX FIFO Size is the remainder of the unallocated FIFO space (16384 bytes – TX FIFO Size). The RX
Status FIFO size is always equal to 1/16 of the RX FIFO Size. The RX Status FIFO length is subtracted
from the total RX FIFO size with the remainder being the RX data FIFO Size.
For example, if TX_FIF_SZ = 6 then:
Total TX FIFO Size = 6144 Bytes (6KB)
TX Status FIFO Size = 512 Bytes (Fixed)
TX Data FIFO Size = 6144 – 512 = 5632 Bytes
RX FIFO Size = 16384 – 6144 = 10240 Bytes (10KB)
RX Status FIFO Size = 10240 / 16 = 640 Bytes (160 RX Status DWORDs)
RX Data FIFO Size = 10240 – 640 = 9600 Bytes
Table 5.3 shows every valid setting for the TX_FIF_SZ field. Note that settings not shown in this table
are reserved and should not be used.
Note: The RX data FIFO is considered full 4 DWORDs before the length that is specified in the
HW_CFG register.
Table 5.3 Valid TX/RX FIFO Allocations
TX_FIF_SZ
TX DATA FIFO
SIZE (BYTES)
TX STATUS FIFO
SIZE (BYTES)
RX DATA FIFO
SIZE (BYTES)
RX STATUS FIFO
SIZE (BYTES)
2
1536
512
13440
896
3
2560
512
12480
832
4
3584
512
11520
768
5
4608
512
10560
704
6
5632
512
9600
640
7
6656
512
8640
576
8
7680
512
7680
512
9
8704
512
6720
448
10
9728
512
5760
384
11
10752
512
4800
320
12
11776
512
3840
256
13
12800
512
2880
192
14
13824
512
1920
128
SMSC LAN9211
89
DATASHEET
Revision 2.9 (03-01-12)