AM79C976 Datasheet, PDF (288/309 Pages) Advanced Micro Devices – PCnet-PRO™ 10/100 Mbps PCI Ethernet Controller

PRELIMINARY
cation pointer into this descriptor and then
copy that is required by existing drivers, since
changed the ownership to give the descriptor
it is being placed directly into the application
to the Am79C976 controller back at S3. Note
buffer space.
that if steps S1, S2, and S3 have not com-
pleted at this time, a BUFF error will result.
N2
The message on the wire ends.
C7
After filling the second buffer and performing
the last chance lookahead to the next descrip-
tor, the Am79C976 controller will write the sta-
S7
When the driver completes the copy of buffer
number 2 data to the application buffer space,
it begins polling descriptor number 3.
tus and change the ownership bit of descriptor C9 When the Am79C976 controller has finished
number 2.
all data DMA operations, it writes status and
S6 After the ownership of descriptor number 2 has
changes ownership of descriptor number 3.
been changed by the Am79C976 controller, S8 The driver sees that the ownership of descrip-
the next driver poll of the second descriptor will
tor number 3 has changed, and it calls the ap-
show ownership granted to the CPU. The
plication to tell the application that a frame has
driver now copies the data from buffer number
arrived.
2 into the middle section of the application
buffer space. This operation is interleaved with
the C7 and C8 operations.
S9
The application processes the received frame
and generates the next TX frame, placing it
into a TX buffer.
C8
The Am79C976 controller will perform data
DMA to the last buffer, whose pointer is point-
ing to application space. Data entering the
S10 The driver sets up the TX descriptor for the
Am79C976 controller.
least buffer will not need the infamous double
A-3
Am79C976
8/01/00