Packet Type Identification; Table 163: Ethernet Type Mappings - Broadcom BCM1250 User Manual

User Manual
10/21/02
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
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 T
ACKET YPE
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
Ethernet Type Field
16'h0800
16'h0806
<=1500
Other
mac_type_cfg[15:0]
mac_type_cfg[31:16]
mac_type_cfg[47:32]
mac_type_cfg[63:48]
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.
Document 1250_1125-UM100CB-R
a b o v e . T h e r x _ c h _ m s n _ s e l
I
DENTIFICATION

Table 163: Ethernet Type Mappings

Status[57:55] Encoding
3'b000
3'b001
3'b010
3'b011
3'b100
3'b101
3'b110
3'b111
B r oadco m C orp or ati on
BCM1250/BCM1125/BCM1125H
m u s t p o i n t l a t e r
Packet Type
IP v4
ARP
802.3 length
No match
Configurable types.
Section 9: Ethernet MACs Page
i n t h e p a c k e t , i f
Table 163.
281