Cypress S6J3200 Series, Manual

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CHAPTER 21:Ethernet MAC
S6J3200 Series Hardware Manual Document Number: 002-04852 Rev. *G 599
hash_index[00] = da[00] ^ da[06] ^ da[12] ^ da[18] ^ da[24] ^ da[30] ^ da[36] ^ da[42]
da[00]
represents the least significant bit of the first byte received, that is, the multicast/unicast indicator,
and
da[47]
represents the most significant bit of the last byte received.
If the hash index points to a bit that is set in the Hash register then the frame will be matched according to
whether the frame is multicast or unicast.
A multicast match will be signaled if the multicast hash enable bit is set,
da[00]
is “1” and the hash index
points to a bit set in the Hash register.
A unicast match will be signaled if the unicast hash enable bit is set,
da[00]
is “1” and the hash index
points to a bit set in the Hash register.
To receive all multicast frames, the Hash register must be set with all “1” and the multicast hash enable bit
must be set to “1” in the Network Configuration register.
3.5.3.
Copy All Frames (or Promiscuous Mode)
If the copy all frames bit is set in the Network Configuration register then all frames (except those that are
too long, too short, have FCS errors or have RX_ER asserted during reception) will be copied to memory.
Frames with FCS errors will be copied if bit 26 is set in the Network Configuration register.
3.5.4.
Disable Copy of Pause Frames
Pause frames can be prevented from being written to memory by setting the disable copying of pause
frames control bit 23 in the Network Configuration register. When set, pause frames are not copied to
system memory regardless of the copy all frames bit, whether a hash match is found, a type ID match is
identified or if a destination address match is found.
3.5.5.
VLAN Support
An Ethernet encoded 802.1Q VLAN tag looks like this:
TPID (Tag Protocol Identifier) 16 bits TCI (Tag Control Information) 16 bits
8100
h
First 3 bits priority, then CFI bit, last 12 bits VID
The VLAN tag is inserted at the 13 th byte of the frame adding an extra four bytes to the frame. To support
these extra four bytes, the Ethernet MAC can accept frame lengths up to 1536 bytes by setting bit 8 in the
Network Configuration register.
If the VID (VLAN identifier) is null (000
h
) this indicates a priority-tagged frame.
The following bits in the receive buffer descriptor status word give information about VLAN tagged
frames:
−
Bit 21 set if receive frame is VLAN tagged (i.e. Type ID of 8100h).
−
Bit 20 set if receive frame is priority tagged (i.e. Type ID of 8100h and null VID). (If bit 20 is set bit 21
will be set also.)
−
Bit 19, 18, and 17 set to priority if bit 21 is set.
−
Bit 16 set to CFI if bit 21 is set.
The Ethernet MAC can be configured to reject all frames except VLAN tagged frames by setting the
discard non-VLAN frames bit in the Network Configuration register.