Ethernet
Wire
activity:
Ethernet
Controller
activity:
Software
activity:
S10: Driver sets up TX descriptor.
S9: Application processes packet, generates TX packet.
}
S8: Driver calls application
to tell application that
packethas arrived.
S8A: Interrupt latency.
C10: ERP interrupt
}
is generated.
C9: Controller writes descriptor #3.
S7: Driver is swapped out, allowing a non-Ethernet
application to run.
}
S7A: Driver Interrupt Service
Routine executes
C8: Controller is performing intermittent
bursts of DMA to fill data buffer #3.
RETURN.
S6: Driver copies data from buffer #2 to the application
N2:EOM
buffer.
Buffer
#3
C7: Controller writes descriptor #2.
S5: Driver polls descriptor #2.
C6: "Last chance" lookahead to
descriptor #3 (OWN).
S4: Driver copies data from buffer #1 to the application
buffer.
C5: Controller is performing intermittent
bursts of DMA to fill data buffer #2
S3: Driver writes modified application
}
pointer to descriptor #3.
}
Buffer
#2
S2: Driver call to application to
get application buffer pointer.
C4: Lookahead to descriptor #3 (OWN).
C3: SRP interrupt is
S1: Interrupt latency.
}
generated.
C2: Controller writes descriptor #1.
C1: Controller is performing intermittent
bursts of DMA to fill data buffer #1.
Buffer
#1
S0: Driver is idle.
C0: Lookahead to descriptor #2.
N1: 64th byte of packet
{
data arrives.
N0: Packet preamble, SFD
and destination address
are arriving.
22206B-B3
Figure B-3. LAPP Timeline for Two-Interrupt Method
Am79C978
B-9
AMD [ AMD ]
