AM79C971VCW Advanced Micro Devices, AM79C971VCW Datasheet - Page 246

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

Note:
enabled, a 2-buffer per packet implementation can be used.
D-10
This document demonstrates a 3-buffer per packet implementation of LAPP. For PCnet-FAST application with external SRAMs
Descriptor
Descriptor
Descriptor
Descriptor
Descriptor
Descriptor
Descriptor
Descriptor
Descriptor
#1
#2
#3
#4
#5
#6
#7
#8
#9
Figure D4. LAPP 3 Buffer Grouping for Two-interrupt Method
OWN = 1
SIZE = HEADER_SIZE (minimum 64 bytes)
OWN = 1
SIZE = S1+S2+S3+S4
OWN = 0
SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)
OWN = 1
SIZE = HEADER_SIZE (minimum 64 bytes)
OWN = 1
SIZE = S1+S2+S3+S4
OWN = 0
SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)
OWN = 1
SIZE = HEADER_SIZE (minimum 64 bytes)
OWN = 1
SIZE = S1+S2+S3+S4
OWN = 0
SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)
STP = 0
STP = 0
STP = 1
STP = 0
STP = 0
STP = 1
STP = 0
STP = 0
Am79C971
STP = 1
Note that the times needed for tasks S1,
S2, S3, S4, and S6 should be divided by
0.8 microseconds to yield an equivalent
number of network byte times before
subtracting these quantities from the
expected message size A.
A = Expected message size in bytes
S1 = Interrupt latency
S2 = Application call latency
S3 = Time needed for driver to write
S4 = Time needed for driver to copy
S6 = Time needed for driver to copy
to third descriptor
data from buffer #1 to
application buffer space
data from buffer #2 to
application buffer space
19364D-D4