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
348
Section 10: Serial Interfaces
Document
1250_1125-UM100CB-R
Upon completion of the DMA transfer, any error indications forwarded through the RxFIFO are reported as
status bits in the first descriptor for the corresponding frame.
lists the DMA status bits that are used
by the receiver’s serial DMA channel.
In addition, a cumulative error summary is maintained in the
ser_status
register. The receive errors are
rx_crc_error, rx_abort, rx_octet_error, rx_longframe_error, rx_shortframe_error and rx_overrun error. When
enabled by the corresponding bit in ser_err_mask, any set bit in
ser_status
generates a request for a serial
device interrupt. Reading the
ser_status
register sets all bits to zero and clears the interrupt condition.
O
PERATION
IN
T
RANSPARENT
M
ODE
In transparent mode, bit streams are sent and received without modification. Frames are not self-identifying,
but a frame structure can be imposed on the bit stream by external synchronization signals. For both transmit
and receive, serialization of each byte can be either least significant bit first or most significant bit first,
according to the setting of msb_first in the
ser_mode
configuration register. Bytes are transmitted and
received in order of increasing address according to the system endian mode.
In transparent mode, the following functions may be performed:
•
address matching (optional)
•
padding of short frames to a configured minimum frame size (optional)
•
CRC calculation and checking (optional)
In transparent mode, the data is framed by implicit start and stop indications at the bit level. The details depend
upon configuration of the line interface.
Table 228: Status Flags for Synchronous Serial Receive Channel
Receive Status Flags
Bits
Name
Default
Description
55:50 reserved
6'b0 Reserved
56
crc_error
1'b0
This bit is set if the received packet has a bad CRC.
57
abort
1'b0
This bit is set if the received packet ended with the abort flag.
58
octet_error
1'b0
This bit is set if the size of the received packet was not a multiple of 8 bits.
59
longframe_error
1'b0
This bit is set if the size of the received packet is bigger than the maximum frame
size.
60
shortframe_error
1'b0
This bit is set if the size of the received packet is shorter than the minimum frame
size.
61
overun_error
1'b0
This bit is set if the received packet overan the FIFO and is therefore invalid.
62
good
1'b0
This bit is set if the received packet has no errors.
63
SOP
1'b0
This bit is set to indicate the start of the packet and the other bits are valid. Software
should ensure this bit is clear when it sets up the descriptor, the DMA controller will
only set it when packet reception has been completed.
Note
The last time-slot specified in the user-defined table should always be enabled.