PM3350-SW datasheet(87/224 Pages) PMC

87 / 224 page

ELAN 8X10

PM3350 ELAN 8 X10

DATA SHEET

PMC-970109

ISSUE 3

8 PORT ETHERNET SWITCH

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND PMC-SIERRA, INC. CUSTOMERS ONLY

Expansion Port Descriptor Structure

Each expansion port descriptor is assigned to a logical device, with indices ranging from

0 through 7. The expansion port descriptor structures are mapped into the memory

locations as given in the foregoing address map, with the structure corresponding to

logical device index zero being mapped into the lowest memory address, and so on. An

expansion port descriptor occupies 16 bytes, and is formatted as follows:

24 23

16 15

8 7

0 Byte Offset

ChipNum

FirstDD

CtrMask

LastDD

reserved

MaxBuffers

RemoteDD

FirstDD:

24-bit pointer to first data descriptor waiting in transfer queue to be

transferred to remote device.

ChipNum:

8-bit index assigned to remote chip corresponding to this expansion port

descriptor; must be 0 for expansion port descriptor zero, and so on.

LastDD:

24-bit pointer to last data descriptor in transfer queue for this remote device.

CtrMask:

8-bit mask passed to DMA hardware when attempting to increment a request

or acknowledge counter in the remote device; must correspond to ChipNum.

MaxBuffers:

16-bit count of packet buffers that remain to be allocated to hold incoming

frames transferred from the remote device; when this count goes to zero, no

more frames will be transferred.

RemoteDD:

32-bit PCI address of next data descriptor pointing to frame to be transferred

from remote device. Generally, the uppermost 8 bits of this field remain

constant, and give the upper 8 bits of the PCI base address set for the

remote device; the lower 24 bits vary, and give the offset of the data

descriptor with reference to the PCI base address.

The FirstDD and the LastDD fields serve to control the transfer queue for frames

waiting to be transferred to the remote device associated with this expansion port

descriptor. FirstDD contains the 24-bit memory address of the data descriptor at the

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