BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
304
Section 9: Ethernet MACs
Document
1250_1125-UM100CB-R
43
bypass_fcs_chk
1'b0
If this bit is set then the interface will perform the FCS check on packets received
in Packet FIFO mode. The last four bytes are checked for a valid CRC-32 using
the same algorithm as for Ethernet. The status will be recorded in the receive
DMA descriptor status field.
If this bit is clear no FCS check is done and all packets will be marked as having
a correct CRC.
Used in Packet FIFO modes.
44
rx_ch_sel_msb
1'b0
This is the top bit of rx_ch_sel (see bits 63:57).
Used in Ethernet and Packet FIFO modes.
45
split_ch_sel
1'b0
System revision < PERIPH_REV3: Reserved
System revision PERIPH_REV3 or later: If this bit is set the 8 bit index used to
select the receive channel number is made up from nibbles extracted from two
different places in the packet, {rx_ch_sel_msb,rx_ch_sel} specify the offset of the
lower 4 bits of the index, rx_ch_msn_sel (in the mac_adfilter register) specify the
upper 4 bits. If split_ch_sel is zero then {rx_ch_sel_msb,rx_ch_sel} is used to
select the low 4 bits of the index and the upper 4 bits is always the next nibble.
Used in Ethernet and Packet FIFO modes.
53:46
bypass_ifg
8'b0
This field gives the number of clock cycles of inter-frame gap that is inserted in
Packet FIFO mode.
If the transmitter is set to append a CRC then this field has a minimum value of
3 in 16 bit FIFO mode and a minimum value of 7 in 8 bit FIFO mode. If CRCs are
never inserted then packets may be transmitted back to back.
Used in Packet FIFO modes.
54
fc_sel
1'b0
This bit is used by software to force flow control. If it is set then flow control will
be asserted on the link (Pause frames in full duplex Ethernet, backpressure by
the method encoded in the fc_cmd bits for half duplex Ethernet, or the link level
flow control pin RXFC for encoded Packet Fifo mode). Flow control will remain
asserted until this bit is cleared. Note that if this bit is set while the mac is disabled
the results are UNPREDICTABLE.
Used in Ethernet and Packet FIFO modes.
56:55
fc_cmd
2'b0
This field sets the flow control style to be used for both software flow control (set
by bit 54) and automatic flow control from the receive DMA channels.
This field is only used for Half Duplex links.
00: Disabled
01: Enabled using collisions
10: Enabled using false carrier
11: UNPREDICTABLE
Used in Ethernet mode only.
63:57
rx_ch_sel
7'b0
This field along with the rx_ch_sel_msb bit sets the offset into received packets
to extract 8 bits to select the receive DMA channel. This offset is in nibbles. If bit
[57] is zero then bits [44, 63:58] give the byte of the packet (starting from zero)
that will be used to index the channel select table. If bit [57] is one then the top
four bits of the byte indexed by [44, 63:58] will be used as the low four bits to
index the channel select table, and the lower four bits from the next byte of the
packet will be used as the upper four bits to index the channel select table.
Used in Ethernet and Packet FIFO modes.
Table 176: MAC Configuration Registers
(Cont.)
mac_cfg_0 -
00_1006_4100
mac_cfg_1 -
00_1006_5100
mac_cfg_2 -
00_1006_6100
This register is used in both Ethernet and Packet FIFO modes
Bits
Name
Default
Description