PM3350-SW datasheet(89/224 Pages) PMC

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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

port logic to reduce the frequency of request interrupts upon request by the firmware

when MaxBuffers goes to zero.

The RemoteDD field holds the 32-bit PCI address of the data descriptor at the head of

the remote device's frame transfer queue assigned to this ELAN 8x10 (i.e., the

counterpart of the local frame transfer queue maintained by the FirstDD/LastDD pair in

this expansion port descriptor.) This field is set up during system initialization. The

uppermost 8 bits are loaded with the 8 MSBs of the PCI base address of the remote

device. The lower 24 bits are loaded with the FirstDD field of the expansion port

descriptor in the remote device (i.e., the address of the empty data descriptor initially

allocated to the remote device's transmit queue.) After frame transfer from the remote

device begins, the uppermost 8 bits of the RemoteDD field remain the same, but the

lower 24 bits are progressively updated by the firmware as frames are copied from the

remote device. The frame transfer queue discipline described above makes the

updating of this field simple: the NextDD field of the last data descriptor to be copied

from the remote device is simply loaded into the lower 24 bits of the RemoteDD field. (It

will be obvious that the 24 LSBs of the RemoteDD field in this ELAN 8x10 device will

always equal the FirstDD field in the expansion port descriptor of the remote device,

i.e., the head of the frame transfer queue.)

As already noted, the expansion port descriptor corresponding to the index assigned to

the ELAN 8x10 device itself (i.e., the device implementing the expansion port

descriptor) is not used. Thus expansion port descriptor 0 in device 0 is not used,

expansion port descriptor 1 in device 1 is not used, and so on. (Obviously, it is

meaningless for a device to transfer frames to

itself across the PCI bus.)

Unlike local port descriptors, the data queued on an expansion port descriptor need not

be restricted to Ethernet frames. Inter-device messages are exchanged by formatting

them into packet buffers and then placing them on the expansion port descriptor

transfer queues corresponding to the target devices. The data descriptor flags should

be set up properly to ensure that the messages are handled specially by the remote

devices, and not treated as normal Ethernet frames. If the message is sufficiently

compact, the packet buffers may be dispensed with and the entire message can be

packed into the data descriptor; in this case, the FirstPB field of the data descriptor

should be set to a NULL.

The expansion port descriptor structures are all cached by the Switch Processor in its

data cache during normal operation; hence the in-memory copies of the expansion port

descriptors may be out-of-date, and cannot be read directly from the PCI bus interface

in a reliable manner unless a data cache flush is performed first via the message

interface.

PM3350-SW Datasheet(PDF) 89 Page - PMC-Sierra, Inc

PM3350-SW Datasheet(HTML) 89 Page - PMC-Sierra, Inc

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