DS537 Datasheet, PDF (81/148 Pages) Xilinx, Inc – LogiCORE IP XPS LL TEMAC

LogiCORE IP XPS LL TEMAC (v2.03a)
Unfortunately, the TEMAC core will prevent receiving any multicast frames if they do not match one of the 4 entries
in the built-in multicast address table. As a result, the TEMAC core will have to be placed in promiscuous address
mode to force it to pass all multicast frames through to the extended multicast address filtering logic.
However, this means it will also pass through all unicast address frames. In order to not increase the processor load
for unicast address filtering, additional unicast address filtering will have to be added to the extended multicast
address filtering logic. The user must make sure that the TEMAC core is in promiscuous receive address mode
when using this extended multicast address filtering mode.
Implementation Details
Received multicast frames that meet all other hardware verification requirements will receive a first level address
filtering in hardware. Frames that pass this initial filtering will be passed up to software drivers with information
provided by hardware to assist the software drivers in providing the second level/final address filtering. If the
frame does not pass hardware filtering, the frame will be dropped and no action will be required by the software
drivers.
While a MAC multicast address is defined as any 48 bit MAC address that has bit 0 (LSb) set to 1 (for example
01:00:00:00:00:00), in most cases the MAC multicast address is created from a IP multicast address as shown in
Figure 51. It is these IP multicast addresses that are a subset of MAC multicast addresses that are filtered by the
extended multicast address filtering mode.
X-Ref Target - Figure 51
224.0.0.0 to 239.255.255.255
multicast bit
(bit 0 byte 0)
32-bit IP multicast address
(typically shown as four 8-bit
values in decimal)
lower 23 bits
01:00:5e:00:00:00 to 01:00:5e:7f:ff:ff
48-bit MAC destination multicast
address (typically shown as six
Constant
8-bit values in hexadecimal)
Hardware looks up the upper
15 bits of 23 bits for ‘1’ or ‘0’
32K x 1
Table
If ‘0’, this
frame can
be dropped.
If ‘1’, pass up to
software to make decision
DS537_51_091909
Figure 51: Mapping IP Multicast Addresses to MAC Multicast Addresses
When a multicast address frame is received while this extended multicast filtering is enabled, the xps_ll_temac first
verifies that the first 24 bits are 01:00:5E and then will use the upper 15 bits of the unique 23 bit MAC multicast
address to index this memory. If the associated memory location contains a 1 then the frame is accepted and passed
up to software for a comparison on the full 23-bit address. If the memory location is a 0 or the upper 24 bits are not
01:00:5E then the frame is not accepted and it is dropped.
The memory is 1-bit wide but is addressed on 32-bit word boundaries. The memory is 32K deep. This table must be
initialized by software via the PLB interface
When using the extended multicast address filtering, the TEMAC must be set to promiscuous mode so that all
frames are available for filtering. When doing this the TEMAC no longer checks for a unicast address match.
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