DM9008F datasheet(38/68 Pages) ETC

38 / 68 page

DM9008

ISA/Plug & Play Super Ethernet Contoller

Final

Version :DM9008-DS-F02

June 14, 2000

Remote DMA

The Remote DMA channel is used both to assemble packets

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 and

Send Packet. Two register pairs are used to control the

Remote DMA: Remote Start Address (RSAR0, RSAR1) and

Remote Byte Count (RBCR0, RBCR1). The Start Address

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 I/O 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 I/O port and sequentially write it to local buffer

memory beginning at the Remote Start Address. 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 reaches a count of 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, beginning

at the Remote Start Address, and write data to the I/O 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 reaches

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

the Receive Byte Count fields found in the Buffer Header of

each packet. After the data are 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 DM9008 to correctly execute the

Send Packet Command, the upper Remote Byte

Count Register (RBCR1) must

first be loaded

with 0FH.

Note 2: The Send Packet command cannot be used with

68000-type processors.

Packet Encapsulation/Decapsulation

A standard IEEE 802.3 packet consists of the following fields:

preamble, Start of Frame Delimiter (SFD), destination address,

source address, length, data and Frame Check Sequence

(FCS). The typical format is shown on the following page. The

packets areManchester encoded and decoded by the ENA

and transferred serially to the ENC using NRZ data with a

clock. All fields are of fixed length except for the data field.

DM9008 generates and appends the preamble, SFD and FCS

fields during transmission. The Preamble and SFD fields are

stripped during reception. (The CRC is passed through to

buffer

memory during reception.)

IEEE 802.3 Packet Format

DM9008F Datasheet(PDF) 38 Page - List of Unclassifed Manufacturers

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