DM9008F datasheet(42/68 Pages) ETC

42 / 68 page

DM9008

ISA/Plug & Play Super Ethernet Contoller

Final

Version :DM9008-DS-F02

June 14, 2000

Removing Packets from the Ring

Packets are removed from the ring using either the Remote

DMA or an external device. When the Remote DMA is used,

the Send Packet command can be used. This programs the

Remote DMA to automatically remove the received packet

pointed to by the Boundary Pointer. At the end of the transfer,

DM9008 moves the Boundary Pointer, freeing additional

buffers for reception. The Boundary Pointer can also

moved manually by programming BNRY. Care should be

taken to keep BNRY at least one buffer behind CURR.

Storage Format for Received Packets

The following diagrams describe the format used by the local

DMA channel for placing received packets into memory. These

modes are selected in the Data Configuration Register (DCR).

D15

Next Packet Pointer

Receive Status

Receive Byte Count 1

Receive Byte Count 0

Byte 2

Byte 1

BOS=0, WTS=1 in DCR

This format is used with Series 32000 808X-type processors.

D15

Next Packet Pointer

Receive Status

Receive Byte Count 0

Receive Byte Count 1

Byte 1

Byte 2

BOS=1, WTS=1 in DCR

This format is used with 68000-type processors.

Receive status

Next Packet Pointer

Receive Byte Count 0

Receive Byte Count 1

Byte 1

Byte 2

BOS=0, WTS=0 in DCR

This format is used with general 8-bit CPUs.

For compatibility with the NE2000 and NE1000, it is essential

to program DCR with BOS=0.

Packet Transmission

The local DMA is also used during transmission of a packet.

Three registers control the DMA transfer during transmission:

a Transmit Page Start Address Register (TPSR) and the

Transmit Byte Count Registers (TBCR0, 1). When the DM9008

receives a command to transmit the packet pointed to by these

registers, buffer memory data will be moved into the FIFO as

required during transmission. DM9008 will generate and

append the preamble, Synch and CRC fields.

Transmit Packet Assembly

DM9008 requires a contiguous assembled packet with the

format

shown.

The transmit

byte count

includes

the

Destination Address, Source Address, Length of Field and

Data. It does not include preamble and CRC. When fewer than

46 bytes are transmitted, the packet must be padded to the

minimum size of 64 bytes. The programmer is responsible for

adding and stripping pad bytes.

DESTINATION ADDRESS

6 bytes

SOURCE ADDRESS

6 bytes

TYPE LENGTH

2 bytes

DATA

≥ 64 bytes

PAD (IF DATA < 46 BYTES)

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