am79c961 Advanced Micro Devices, am79c961 Datasheet - Page 166

• Manufacturer Part Number: am79c961
• Description: Pcnettm-isa Jumperless Single-chip Ethernet Controller For Isa
• Manufacturer: Advanced Micro Devices

The controller will discard all descriptors with OWN = 1
and STP = 0 and move to the next descriptor when
searching for a place to begin a new frame . It dis-
cards these desciptors by simply changing the owner-
ship bit from OWN=1 to OWN = 0. Such a descriptor is
unused for receive purposes by the controller, and the
driver must recognize this. (The driver will recognize
this if it follows the software rules.)
The controller will ignore all descriptors with OWN = 0
and STP = 0 and move to the next descriptor when
searching for a place to begin a new frame . In other
words, the controller is allowed to skip entries in the ring
that it does not own, but only when it is looking for a
place to begin a new frame.
1-640
*ENP or ERR
Descriptor
AMD
Number
etc.
1
2
3
4
5
6
OWN
1
1
0
1
1
0
1
Frame Arrived
Before the
STP
1
0
0
1
0
0
1
ENP*
X
X
X
X
X
X
X
Am79C961
OWN
0
0
0
1
1
0
1
Frame Has Arrived
Some Examples of LAPP Descriptor
Interaction
Choose an expected frame size of 1060 bytes.
Choose buffer sizes of 800, 200 and 200 bytes.
1)
After the
Assume that a 1060 byte frame arrives correctly,
and that the timing of the early interrupt and the
software is smooth. The descriptors will have
changed from:
STP
1
0
0
1
0
0
1
ENP*
X
X
X
X
0
0
1
(After Frame Arrival)
Bytes 1–800
Bytes 801–1000
Bytes 1001–1060
Controller’s current
location
Not yet used
Not yet used
Not yet used
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