DM9102DEP datasheet(48/70 Pages) DAVICOM

48 / 70 page

Final

Version: DM9102D-DS-F01

May 10, 2006

7.2.3 Transmit Data Buffer Processing

Refer to Figure 7-3. When start/stop transmit command is

set and the DM9102D 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 DM9102D 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

DM9102D 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 DM9102D can resume.

Transmit Buffer Management State Transition

Figure 7-3

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

Stop Transmit Command or

Reset Command

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