AM79C971VCW Advanced Micro Devices, AM79C971VCW Datasheet - Page 239

• Manufacturer Part Number: AM79C971VCW
• Description: PCnet-FAST Single-Chip Full-Duplex 10/100 Mbps Ethernet Controller for PCI Local Bus
• Manufacturer: Advanced Micro Devices

S6
C8
N2
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.
Am79C971
S7
C9
S8
S9
S10
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.
The driver sets up the TX descriptor for the
Am79C971 controller.
D-3