AM79C970 datasheet(157/168 Pages) AMD

157 / 168 page

AMD

1-1024

Am79C970

C7:

After filling the second buffer and performing the

last chance lookahead to the next descriptor, the

PCnet-PCI controller will write the status and

change the ownership bit of descriptor number 2.

S6:

After the ownership of descriptor number 2 has

been changed by the PCnet-PCI controller, the

next driver poll of the 2nd descriptor will show

ownership granted to the CPU. The driver now

copies the data from buffer number 2 into the mid-

dle section of the application buffer space. This

operation is interleaved with the C7 and C8

operations.

C8:

The PCnet-PCI controller will perform data DMA

to the last buffer, whose pointer is pointing to ap-

plication space. Data entering the last buffer will

not need the infamous double copy that is required

by existing drivers, since it is being placed directly

into the application buffer space.

N2:

The message on the wire ends.

S7:

When the driver completes the copy of buffer

number 2 data to the application buffer space, it

begins polling descriptor number 3.

C9:

When the PCnet-PCI controller has finished all

data DMA operations, it writes status and changes

ownership of descriptor number 3.

S8:

The driver sees that the ownership of descriptor

number 3 has changed, and it calls the application

to tell the application that a frame has arrived.

S9:

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

PCnet-PCI controller.

AM79C970 Datasheet(PDF) 157 Page - Advanced Micro Devices

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