LAN9211 datasheet(89/147 Pages) SMSC

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High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX Support

Datasheet

SMSC LAN9211

Revision 2.9 (03-01-12)

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)

1536

512

13440

896

2560

512

12480

832

3584

512

11520

768

4608

512

10560

704

5632

512

9600

640

6656

512

8640

576

7680

512

7680

512

8704

512

6720

448

9728

512

5760

384

10752

512

4800

320

11776

512

3840

256

12800

512

2880

192

13824

512

1920

128

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