DM9102AT datasheet(55/77 Pages) ETC

55 / 77 page

DM9102A

Single Chip Fast Ethernet NIC controller

Final

Version: DM9102A-DS-F03

August 28, 2000

2. Transmit Data Buffer Processing

When start/stop transmit command is set and the DM9102A

is in running state, transmit process polls transmit descriptor

list for frames requiring transmission. When it completes a

frame transmission, the status related to the transmitted

frame will be written into the transmit descriptor. If the

DM9102A detects a descriptor flagged as owned by the

host and no transmit buffers are available, transmit process

will be suspended. While in the running state, transmit

process can simultaneously acquire two frames. As transmit

process completes copying the first frame, it immediately

polls transmit descriptor list for the second frame. If the

second frame is valid, transmit process copies the frame

before writing the status information of the first frame.

Both conditions will make transmit process suspend. (i) The

DM9102A detects a descriptor owned by the host. (ii) A

frame transmission is aborted when a locally induced error is

detected. Under either condition, the host driver has to

service the condition before the DM9102A can resume.

Stop State

Descriptor

Access

Data

Transfer

Write

Status

Suspended

Buffer Available

( OWN bit = 1 )

Frame Fully Transmited

Start Transmit Command Or

Transmit Poll Command

Under FIFO Threshold

Buffer not Empty

Buffer Empty

Transmit Buffer Unavailable

( Owned By Host )

Transmit Poll Command

Stop Transmit Command Or

Reset Command

Transmit Buffer Management State Transition

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