am79c961 Advanced Micro Devices, am79c961 Datasheet - Page 167

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

2)
*ENP or ERR
** Note that the PCnet-ISA
1) If the controller finishes the data transfers into buffer number 2 after the driver writes the application’s modified buffer pointer
2) If the controller finishes the data transfers into buffer number 2 before the driver writes the application’s modified buffer
into the third descriptor, then the controller will write a ZERO to ENP for this buffer and will write a ZERO to OWN and STP.
pointer into the third descriptor, then the controller will complete the frame in buffer number two and then skip the then un-
owned third buffer. In this case, the PCnet-ISA
descriptor, and it is possible that the software left this bit as ENP=1 from the last time through the ring. Therefore, the soft-
ware must treat the location as a don’t care; The rule is, after finding ENP=1 (or ERR=1) in descriptor number 2, the software
must ignore ENP bits until it finds the next STP=1.
Descriptor
Assume that instead of the expected 1060 byte
frame, a 900 byte frame arrives, either because
there was an error in the network, or because this is
the last frame in a file transmission sequence.
Number
etc.
1
2
3
4
5
6
OWN
1
1
0
1
1
0
1
+
controller might write a ZERO to ENP location in the 3rd descriptor. Here are the two possibilities:
Frame Arrived
Before the
STP
1
0
0
1
0
0
1
ENP*
X
X
X
X
X
X
X
+
controller will not have had the opportunity to RESET the ENP bit in this
Am79C961
OWN
0
0
0
1
1
0
1
Frame Has Arrived
After the
STP
1
0
0
1
0
0
1
ENP*
?**
X
X
X
X
0
1
(After Frame Arrival)
Bytes 1–800
Bytes 801–900
Discarded buffer
Controller’s current
location
Not yet used
Not yet used
Not yet used
Comments
AMD
1-641