am79c961 Advanced Micro Devices, am79c961 Datasheet - Page 164

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

C8: The PCnet-ISA
N2: The message on the wire ends.
S7: When the driver completes the copy of buffer num-
1-638
operation is interleaved with the C7 and C8
operations.
to the last buffer, whose pointer is pointing to appli-
cation space. Data entering the last buffer will not
need the infamous “double copy” that is required by
existing drivers, since it is being placed directly into
the application buffer space.
ber 2 data to the application buffer space, it begins
polling descriptor number 3.
AMD
N2: EOM
N0: Packet preamble, SFD
Ethernet
activity:
and destination address
are arriving.
Wire
{
N1: 64th byte of packet
C9: Controller writes descriptor #3.
C8: Controller is performing intermittent
C7: Controller writes descriptor #2.
C6: "Last chance" lookahead to
C5: Controller is performing intermittent
C4: Lookahead to descriptor #3 (OWN).
C3: SRP interrupt
C2: Controller writes descriptor #1.
C1: Controller is performing intermittent
C0: Lookahead to descriptor #2.
+
data arrives.
controller will perform data DMA
bursts of DMA to fill data buffer #3.
descriptor #3 (OWN).
bursts of DMA to fill data buffer #2.
is generated.
bursts of DMA to fill data buffer #1.
Figure 1. Look Ahead Packet Processing (LAPP) Timeline
}
Controller
Ethernet
activity:
Buffer
Buffer
Buffer
#3
#2
#1
Am79C961
C9: When the PCnet-ISA
S8: The driver sees that the ownership of descriptor
S9: The application processes the received frame and
S10: The driver sets up the TX descriptor for the
S10: Driver sets up TX descriptor.
S9: Application processes packet, generates TX packet.
S7: Driver polls descriptor of buffer #3.
S6: Driver copies data from buffer #2 to the application buffer.
S5: Driver polls descriptor #2.
S4: Driver copies data from buffer #1 to the application buffer.
S1: Interrupt latency.
S0: Driver is idle.
Software
activity:
data DMA operations, it writes status and changes
ownership of descriptor number 3.
number 3 has changed, and it calls the application
to tell the application that a frame has arrived.
generates the next TX frame, placing it into a TX
buffer.
PCnet-ISA
} {
{
+
S8: Driver calls application
S3: Driver writes modified application
S2: Driver call to application to
controller.
to tell application that
packet has arrived.
pointer to descriptor #3.
get application buffer pointer.
+
controller has finished all
18183B-79