DP83902A datasheet(23/70 Pages) NSC

23 / 70 page

90 Remote DMA

The Remote DMA channel is used to both assemble pack-

ets for transmission and to remove received packets from

the Receive Buffer Ring It may also be used as a general

purpose slave DMA channel for moving blocks of data or

commands between host memory and local buffer memory

There are three modes of operation Remote Write Remote

Read or Send Packet

Two register pairs are used to control the Remote DMA a

Remote Start Address (RSAR0 RSAR1) register pair and a

Remote Byte Count (RBCR0 RBCR1) register pair The

Start Address Register pair points to the beginning of the

block to be moved while the Byte Count Register pair is

used to indicate the number of bytes to be transferred Full

handshake logic is provided to move data between local

buffer memory and a bidirectional IO port

REMOTE WRITE

A Remote Write transfer is used to move a block of data

from the host into local buffer memory The Remote DMA

will read data from the IO port and sequentially write it to

local buffer memory beginning at the Remote Start Address

The DMA Address will be incremented and the Byte Coun-

ter will be decremented after each transfer The DMA is

terminated when the Remote Byte Count Register reaches

zero

REMOTE READ

A Remote Read transfer is used to move a block of data

from local buffer memory to the host The Remote DMA will

sequentially read data from the local buffer memory begin-

ning at the Remote Start Address and write data to the IO

port The DMA Address will be incremented and the Byte

Counter will be decremented after each transfer The DMA

is terminated when the Remote Byte Count Register reach-

es zero

SEND PACKET COMMAND

The Remote DMA channel can be automatically initialized

to transfer a single packet from the Receive Buffer Ring

The CPU begins this transfer by issuing a ‘‘Send Packet’’

Command The DMA will be initialized to the value of the

Boundary Pointer Register and the Remote Byte Count

of the Receive Byte Count fields found in the Buffer Header

of each packet After the data is transferred the Boundary

Pointer is advanced to allow the buffers to be used for new

receive packets The Remote Read will terminate when the

Byte Count equals zero The Remote DMA is then prepared

to read the next packet from the Receive Buffer Ring If the

DMA pointer crosses the Page Stop Register it is reset to

the Page Start Address This allows the Remote DMA to

remove packets that have wrapped around to the top of the

Receive Buffer Ring

Note 1

In order for the ST-NIC to correctly execute the Send Packet Com-

mand the upper Remote Byte Count Register (RBCR1) must first

be loaded with 0FH

Note 2

The Send Packet command cannot be used with 680x0 type proc-

essors

Remote DMA Autoinitialization from Buffer Ring

TLF11157 – 17

DP83902A 数据表(PDF) 23 Page - National Semiconductor (TI)

DP83902A 数据表(HTML) 23 Page - National Semiconductor (TI)

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

数据表下载