7-45
PERIPHERAL SUBSYSTEM
Figure 7-24. 82596 Shared Memory
The coprocessor executes its command list from shared memory and, in parallel, receives frames
from the network and places them in shared memory. The processor manages the shared memory,
which contains command chains and bidirectional data chains. The coprocessor executes the
command chains. An on-chip DMA controls four channels, which allow autonomous transfers of
data blocks independently of the processor. Buffers containing erroneous or collided frames can
be automatically recovered without processor intervention. The processor becomes involved only
after a command sequence has finished executing, or after a sequence of frames has been received
and stored, ready for processing.
In addition to this normal operating mode, the processor can initiate a port access in the copro-
cessor. This mode may be entered whenever the coprocessor is not actively driving the bus. It
allows the processor to write an alternate system configuration pointer, write an alternate dump
command and pointer (used for troubleshooting a no-response problem), perform a software re-
set, or perform a self-test.
82596
LAN
Controller
Intel486™
INTA#
Processor
Initialization
Root
System Control
Block Mailbox
Shared Memory
INT/INT#
Receive
Frame
Area
Command
Line
Transmit
Buffer
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