AM79C971VCW datasheet(239/265 Pages) AMD

239 / 265 page

Am79C971

D-3

tus and change the ownership bit of descriptor

number 2.

After the ownership of descriptor number 2 has

been changed by the Am79C971 controller, the

next driver poll of the second descriptor will

show ownership granted to the CPU. The driver

now copies 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 Am79C971 controller will perform data

DMA to the last buffer, whose pointer is pointing

to application space. Data entering the last buff-

er will not need the infamous double copy that

is required by existing drivers, since it is being

placed directly 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 Am79C971 controller has finished all

data DMA operations, it writes status and

changes ownership of descriptor number 3.

The driver sees that the ownership of descriptor

number 3 has changed, and it calls the appli-

cation 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

Am79C971 controller.

AM79C971VCW Datasheet(PDF) 239 Page - Advanced Micro Devices