參數(shù)資料
型號: AM79C970
廠商: Advanced Micro Devices, Inc.
英文描述: PCnetTM-PCI Single-Chip Ethernet Controller for PCI Local Bus
中文描述: PCnetTM - PCI單芯片以太網(wǎng)控制器的PCI總線
文件頁數(shù): 164/168頁
文件大?。?/td> 943K
代理商: AM79C970
AMD
1-1031
Am79C970
Figure D4 shows the buffer sizing for the two-interrupt
method. Note that the second buffer size will be about
the same for each method.
18220A-58
A = Expected message size in bytes
S1 = Interrupt latency
S2 = Application call latency
S3 = Time needed for driver to write
to third descriptor
S4 = Time needed for driver to copy
data from buffer #1 to
application buffer space
S6 = Time needed for driver to copy
data from buffer #2 to
application buffer space
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.
OWN = 1
SIZE = HEADER_SIZE (minimum 64 bytes)
STP = 1
Descriptor
#1
OWN = 1
SIZE = S1+S2+S3+S4
STP = 0
Descriptor
#2
OWN = 0
SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)
STP = 0
Descriptor
#3
OWN = 1
SIZE = HEADER_SIZE (minimum 64 bytes)
STP = 1
Descriptor
#4
OWN = 1
SIZE = S1+S2+S3+S4
Descriptor
#5
STP = 0
Descriptor
#6
OWN = 0
SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)
STP = 0
OWN = 1
SIZE = HEADER_SIZE (minimum 64 bytes)
STP = 1
Descriptor
#7
OWN = 1
SIZE = S1+S2+S3+S4
Descriptor
#8
STP = 0
Descriptor
#9
OWN = 0
SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)
STP = 0
Figure D4. LAPP 3 Buffer Grouping for TWO-INTERRUPT Method
There is another alternative which is a marriage of the
two previous methods. This third possibility would use
the buffer sizes set by the two-interrupt method, but
would use the polling method of determining frame end.
This will give good frame latency but at the price of very
high CPU utilization.
And still, there are even more compromise positions that
use various fixed buffer sizes and effectively, the flow of
the one-interrupt method. All of these compromises will
reduce the complexity of the one-interrupt method by re-
moving the heuristic buffer sizing code, but they all
become less efficient than heuristic code would allow.
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