LAN9220 datasheet(77/142 Pages) MICROCHIP

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 2006-2017 Microchip Technology Inc.

DS00002417A-page 77

LAN9220

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 pay-

load 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.

Soft Reset (SRST). Writing 1 generates a software initiated reset. This reset

generates a full reset of the MAC CSR’s. The SCSR’s (system command

and status registers) are reset except for any NASR bits. Soft reset also

clears any TX or RX errors (TXE/RXE). This bit is self-clearing.

Note:

• Do not attempt a soft reset unless the PHY is fully awake and opera-

tional. After a PHY reset, or when returning from a reduced power state,

the PHY must given adequate time to return to the operational state

before a soft reset can be issued.

• The LAN9220 must always be read at least once after power-up, reset,

or upon return from a power-saving state or write operations will not

function.

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

Bits

Description

Type

Default

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