LAN9117 datasheet(48/114 Pages) MICROCHIP

48 / 114 page

LAN9117

DS00002267A-page 48

 2005-2016 Microchip Technology Inc.

3.14.1.1

Receive Data FIFO Fast Forward

The RX data path implements an automatic data discard function. Using the RX data FIFO Fast Forward bit (RX_FFWD)

in the RX_DP_CTRL register, the host can instruct the LAN9117 to skip the packet at the head of the RX data FIFO.

The RX data FIFO pointers are automatically incremented to the beginning of the next RX packet.

When performing a fast-forward, there must be at least 4 DWORDs of data in the RX data FIFO for the packet being

discarded. For less than 4 DWORDs do not use RX_FFWD. In this case data must be read from the RX data FIFO and

discarded using standard PIO read operations.

After initiating a fast-forward operation, do not perform any reads of the RX data FIFO until the RX_FFWD bit is cleared.

Other resources can be accessed during this time (i.e., any registers and/or the other three FIFOs). Also note that the

RX_FFWD will only fast-forward the RX data FIFO, not the RX status FIFO.

The receiver does not have to be stopped to perform a fast-forward operation.

3.14.1.2

Force Receiver Discard (Receiver Dump)

In addition to the Receive data Fast Forward feature, LAN9117 also implements a receiver "dump" feature. This feature

allows the host processor to flush the entire contents of the RX data and RX status FIFOs. When activated, the read

and write pointers for the RX data and status FIFOs will be returned to their reset state. To perform a receiver dump, the

LAN9117 receiver must be halted. Once the receiver stop completion is confirmed, the RX_DUMP bit can be set in the

RX_CFG register. The RX_DUMP bit is cleared when the dump is complete. For more information on stopping the

receiver, please refer to Section 3.14.4, "Stopping and Starting the Receiver," on page 49. For more information on the

RX_DUMP bit, please refer to Section 5.3.7, "RX_CFG—Receive Configuration Register," on page 65.

3.14.2

RX PACKET FORMAT

The RX status words can be read from the RX status FIFO port, while the RX data packets can be read from the RX

data FIFO. RX data packets are formatted in a specific manner before the host can read them. It is assumed that the

host has previously read the associated status word from the RX status FIFO, to ascertain the data size and any error

conditions.

FIGURE 3-19:

RX PACKET FORMAT

ofs + First Data DWORD

Last Data DWORD

Host Read

Order

1st

2nd

Last

Optional Pad DWORD0

Optional Pad DWORDn

Optional offset DWORD0

Optional offset DWORDn

LAN9117 Datasheet(PDF) 48 Page - Microchip Technology

LAN9117 Datasheet(HTML) 48 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL