PM3350-SW datasheet(112/224 Pages) PMC

112 / 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

110

transmitted frame, and reads out the reference count from the RefCount field in

the packet buffer. The reference count is decremented, and the result

inspected: if the count is non-zero, then additional queue entries are pointing to

the frame data, and the packet buffer chain should not be freed; instead, the

new reference count is written back to the packet buffer. The Flags field of the

data descriptor is also checked to see if the frame requires special handling.

20. The data descriptor read in the previous step is freed to the free data descriptor

pool, and the transmit queue maintained by the local port descriptor is advanced

to the next entry (if any).

21. If the reference count checked in the preceding step went to zero (or the frame

was a unicast), then the frame does not have to be transmitted out any more

ports; the firmware will then de-allocate the packet buffers holding the frame

back to the free packet buffer pool.

22. The firmware now reads and updates the per-port transmit statistics stored in

the local port descriptor.

23. If the frame was a unicast, then the HashBkt pointer field in the data descriptor

will denote a valid destination hash bucket. The firmware will use this pointer to

access and update the per-MAC transmit statistics in the hash bucket as well.

Note that transmit statistics are not updated on a per-MAC basis in the case of

broadcasts or multicasts.

24. When the above processing has been completed, the firmware will (if it freed up

the packet buffer chain in step 21 above) increment the source port buffer count

by the number of buffers freed in order to restore the buffer limit to its original

value. The source port is obtained via the SrcPort entry in the data descriptor,

which holds the index of the physical port on which the frame arrived (and hence

indicates the local port descriptor containing the MaxBuffers field that must be

incremented). This completes the processing of the frame.

It should be noted that the Switch Processor firmware is actually responsible for re-

transmitting a frame over a local port if the transmission attempt is aborted due to

collision or the need to defer to an incoming frame. This is done automatically by simply

checking the transmit queue associated with that local port whenever it is known that

the DMA Controller channel for that port is idle; if one or more frames are present in the

transmit queue, then the frame at the head of the queue is passed to the DMA

Controller for transmission. This operation is performed at three points in the course of

frame switching: when a frame has just been received (and presumably the MAC logic

is counting out the inter-frame gap), when a frame has just been transmitted, or a

transmit attempt was terminated by a collision, and when a frame is queued for

transmission out the given port.

PM3350-SW Datasheet(PDF) 112 Page - PMC-Sierra, Inc

PM3350-SW Datasheet(HTML) 112 Page - PMC-Sierra, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL