AM79C978VCSLASHW datasheet(243/261 Pages) AMD

243 / 261 page

Am79C978

B-3

After the ownership of descriptor number 2 has

been changed by the controller, the next driver

poll of the second descriptor will show owner-

ship granted to the CPU. The driver now cop-

ies the data from buffer number 2 into the

middle section of the application buffer space.

This operation is interleaved with the C7 and

C8 operations.

The controller will perform data DMA to the last

buffer, whose pointer is pointing to application

space. Data entering the least buffer will not

need the infamous double copy that is required

by existing drivers, since it is being placed di-

rectly into the application buffer space.

The message on the wire ends.

When the driver completes the copy of buffer

number 2 data to the application buffer space,

it begins polling descriptor number 3.

When the controller has finished all data DMA

operations, it writes status and changes own-

ership of descriptor number 3.

The driver sees that the ownership of descrip-

tor number 3 has changed, and it calls the ap-

plication to tell the application that a frame has

arrived.

The application processes the received frame

and generates the next TX frame, placing it

into a TX buffer.

S10

The driver sets up the TX descriptor for the

controller.

AM79C978VC/W 数据表(PDF) 243 Page - Advanced Micro Devices