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
292
Section 9: Ethernet MACs
Document
1250_1125-UM100CB-R
The pin mapping is summarized in the following table:
Other than the external data width and framing options (described below) the Packet FIFO modes use the
same internal data path. The following rules/differences apply in all modes.
•
The speed selection in the
mac_cfg
register must be set for gigabit operation to use the reference input
clock to generate the transmit clock.
•
The IPv4 header checking is not performed. The iphdr_offset field in the
mac_adfilter_cfg
register is not
used and should be set to zero.
•
The address filter is not normally useful in Packet FIFO mode and can be configured to accept all packets
by setting the allpkt_en bit in the
mac_adfilter_cfg
register.
•
The 13th and 14th bytes of the incoming packet are still compared as if they contained an Ethernet type
and the DMA status word in bits [57:55] will still be set as described in
.
•
If the bypass_fcs_chk bit is set in the
mac_cfg
register then received packets will have their final four
bytes checked for a valid CRC-32 (using the same algorithm as for the Ethernet) and the bit in the receive
DMA status word will be set accordingly. If the bypass_fcs_chk bit is clear the status bit will always
indicate the CRC check passed.
•
The receive channel selection is done in the same way as for the Ethernet mode as described in
Section: “Receive DMA Channel Selection” on page 281
.
•
The only transmit options (see
Section: “Data Buffers and Descriptors” on page 147
and
) that can be used in the start of packet descriptor are No Modification (4’b0111)
and Append CRC (4’b001). All other options will give UNPREDICTABLE results.
•
Some modes of the Packet FIFO interface allow packet errors to be signalled. These packets will be
marked as bad in the receive DMA status information. The automatic discard of error packets (described
in the
Section: “Receiver Configuration” on page 275
) should be disabled in Packet FIFO modes.
•
The RMON counters are not incremented when the interface is in Packet FIFO modes.
Table 169: BCM1250 Ethernet/Fifo Pin Usage
E0_ pins
E1_ pins
E2_ pins
All Interfaces Ethernet or 8-bit Fifo
GMII or 8-bit Fifo E0_
GMII or 8-bit Fifo E1_
GMII or 8-bit Fifo E2_
One 16-bit Packet Fifo,
One Ethernet or 8-bit Fifo
16-bit Packet Fifo F0_
GMII or 8-bit Fifo E2_
Two 16-bit Packet Fifos
16-bit Packet Fifo F0_
16-bit Packet Fifo F1_
One 16-bit Packet Fifo,
One 8-bit Packet Fifo
8-bit Fifo E0_
16-bit Packet Fifo F1_