AM79C978VCSLASHW datasheet(250/261 Pages) AMD

250 / 261 page

B-10

Am79C978

Figure B-4.

LAPP 3 Buffer Grouping for Two-interrupt Method

Descriptor

OWN = 1

STP = 1

SIZE = HEADER_SIZE (minimum 64 bytes)

OWN = 1

STP = 0

SIZE = S1+S2+S3+S4

OWN = 0

STP = 0

SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)

OWN = 1

STP = 1

SIZE = HEADER_SIZE (minimum 64 bytes)

OWN = 1

STP = 0

SIZE = S1+S2+S3+S4

OWN = 0

STP = 0

SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)

OWN = 1

STP = 1

SIZE = HEADER_SIZE (minimum 64 bytes)

OWN = 1

STP = 0

SIZE = S1+S2+S3+S4

OWN = 0

STP = 0

SIZE = 1518 - (S1+S2+S3+S4+HEADER_SIZE)

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.

22206B-B4

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