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
285
If the interface is operating in 8 or 16 bit encoded Packet FIFO mode (see
Section: “16-Bit Packet FIFO Operation” on page 299
) the flow control is invoked
by asserting the RXFC signal. In all other Packet FIFO modes flow control is ignored.
I
NTERRUPTS
There are two methods of signalling interrupts from the Ethernet and Packet Fifo interface. The standard
method uses a single system interrupt for all DMA and management interrupts, the split method uses a special
interrupt for DMA channel 1 and the standard interrupt covers channel 0 and management.
The
mac_status
register contains the status information for a MAC. The low 32 bits contain the receive and
transmit status for each of the DMA channels, the upper bits contain error and RMON counter information.
There is a mask register
mac_int_mask
associated with the status register. If a bit is set in both the mask and
status then an interrupt will be raised. Reads to the
mac_status
register have the side effect of clearing latched
interrupt information. The information in the status register may be read with no side effects through the
mac_status_debug
register.
The split_ch1 bit in the mac_int_mask register is used to select between the standard and split methods of
signalling and clearing interrupts. It defaults to 0 to give the standard behaviour.
S
TANDARD
I
NTERRUPT
S
IGNALING
In the standard mode the main interrupt for the MAC is raised whenever any status bit is set and the
corresponding mask bit is set. Reads from the
mac_status
register will clear all latched bits.
S
PLIT
I
NTERRUPT
S
IGNALING
In the split mode the main interrupt for the MAC is raised whenever any channel 0 DMA status bit (from bits
23:16, 7:0) is set and the corresponding mask bit is set, or when any error status bit (from bits 46:40) and
corresponding mask bit is set. Reads from the
mac_status
register will clear all latched bits associated with
channel 0 or errors. The channel 1 interrupt for the MAC will be raised if any channel 1 DMA status bit (from
bits 31:24,15:8) is set and the corresponding mask bit is set. Reads from the
mac_status1
register will clear
all latched bits associated with channel 1.
1
x
x
x
Software pause frames. The pause frame will be received
by software which may use the cpu_pause_en bit to pause
channels, or may use it to cause discard from or reordering
of internal queues. Note that the interrupt service latency
will be part of the flow control loop time, so the link peer will
need larger buffers.
Table 165: Pause Frame Options
(Cont.)
fwdpause_en
ch_base
_fc_en
Ch 0
fc_pause_en
Ch 1
fc_pause_en
Description