User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 9: Ethernet MACs Page
281
The receive channel selection is used in the same way in Packet FIFO mode.
In devices where the system revision indicates PERIPH_REV3 or greater the 8 bit index into the channel
number table can be formed from two four bit fields extracted from the packet. The split_ch_en bit in the
mac_cfg
register enables this feature. The lower 4 bits of the index are extracted from the packet at the offset
specified by the {rx_ch_sel_msb,rx_ch_sel} value and the upper 4 bits of the index are extracted from the offset
specified by the rx_ch_msn_sel field in the
mac_adfilter_cfg
register. Both these are nibble offsets as
d e s c r i b e d a b o v e . T h e r x _ c h _ m s n _ s e l m u s t p o i n t l a t e r i n t h e p a c k e t , i f
rx_ch_msn_sel <= {rx_ch_sel_msb,rx_ch_sel} the channel selected is UNPREDICTABLE. When split_ch_en
is zero the rx_ch_msn_sel value is ignored and the upper 4 bits of the index are the nibble after the
{rx_ch_sel_msb,rx_ch_sel} offset as described above.
P
ACKET
T
YPE
I
DENTIFICATION
The receiver reads the Ethernet packet type field in the inbound packet. Some common packet types are
detected and encoded in the status that is written to the descriptor. Four of the types are fixed, the other four
are programmable in the
mac_type_cfg
register. The packet type encodings are shown in
In Packet FIFO mode the 13th and 14th bytes of the received packet will be checked against the same values
and the three bit encoding will be placed in the descriptor status word. In most cases this value should be
ignored, but it is possible that the four configurable types could be used to identify special packets.
Table 163: Ethernet Type Mappings
Ethernet Type Field
Status[57:55] Encoding
Packet Type
16’h0800
3’b000
IP v4
16’h0806
3’b001
ARP
<=1500
3’b010
802.3 length
Other
3’b011
No match
mac_type_cfg[15:0]
3’b100
Configurable types.
mac_type_cfg[31:16]
3’b101
mac_type_cfg[47:32]
3’b110
mac_type_cfg[63:48]
3’b111
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