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
306
Section 9: Ethernet MACs
Document
1250_1125-UM100CB-R
Table 179: MAC FIFO Threshold Registers
mac_thrsh_cfg_0 -
00_1006_4108
mac_thrsh_cfg_1 -
00_1006_5108
mac_thrsh_cfg_2 -
00_1006_6108
This register is used in both Ethernet and Packet FIFO modes
Bits
Name
Default
Description
6:0
tx_wr_thrsh
7'b0
Transmit FIFO write threshold. Sets the number of free 64 bit entries the transmit FIFO
must have before it signals that space is available. For DMA operation this field must be
set to 4 or 8 entries depending on the state of the tbx_en bit in the
dma_config0
register.
See
Section: “Transmitter Configuration” on page 272
7
reserved 1'b0
Reserved
14:8
tx_rd_thrsh
7'b0
Transmit FIFO read threshold. Sets the number of valid 64 bit entries the transmit FIFO
must hold before the MAC will start transmitting the packet. See
Note that the tx_wr tx_rd_thrsh must be less than the size of the fifo or the
transmitter behaviour is UNPREDICTABLE (tx_wr tx_rd_thrsh <= 32 for parts
with System Revision of 1, tx_wr tx_rd_thrsh <=128 for parts with revision
greater than 2).
15
reserved 1'b0
Reserved
21:16
tx_rl_thrsh
6'b0
Transmit FIFO release count. This sets the number of 64 bit FIFO entries that will be
held in the FIFO when the MAC is configured to hold the start of packets. See the
tx_hold_sop_en bit in the
mac_cfg
register. See
23:22 reserved 2'b0 Reserved
29:24 reserved 6'b0 Reserved
31:30 reserved 2'b0 Reserved
37:32
rx_rd_thrsh
6'b0
Receive read threshold. This field sets the number of entries that must be in the receive
FIFO for it to indicate data is available to be read. For DMA operation this field must be
set to 4 entries. See
Section: “Receiver Configuration” on page 275
39:38 reserved 2'b0 Reserved
45:40
rx_rl_thrsh
6'b0
Receive release threshold. This field sets the number of FIFO entries that must be written
at the start of a packet before any of the data is made available for reading. The data is
also made available if the packet ends before the threshold is reached. See
Section: “Receiver Configuration” on page 275
This field must be greater than 2. If it is zero the MAC receive behavior will be
UNPREDICTABLE.
55:46 reserved 10'b0
Reserved
61:56
enc_fc_thrsh
6’h4
In encoded Packt Fifo modes link level flow control will be requested when the number
of free doublewords in the receive fifo falls below this threshold.
63:62
reserved 2'b0
Reserved
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