cx28365 Mindspeed Technologies, cx28365 Datasheet - Page 79

• Manufacturer Part Number: cx28365
• Description: X12, X6, X4 T3/e3 Framer And Atm Cell Transmission Convergence Sublayer Processor
• Manufacturer: Mindspeed Technologies

CX28365/6/4 Data Sheet
500028C
Normal Message
To modify the basic settings of the RDL (i.e., Near-Full FIFO threshold, FCS
checking, E3-G.832 NR/GC source), the system should first disable the RDL (by
clearing the RxDLEn field of the Receive Data Link Control register).
After disabling the RDL, when accompanied by an immediate termination of all its
activities, the following enable causes discard of all the FIFO buffer contents and
update of the status indications to represent a new status (i.e., all interrupt indications
clear, no data blocks in the FIFO buffer).
Writing Messages into the FIFO
Data arriving on the data link channel is automatically written into the FIFO buffer by
the RDL. Type a1, a2, and b block description references found below are explained in
Table 2-7.
A new data block starts filling up when the RDL detects a transition from flag
sequence 01111110 to stuffed-zero data ( 5 consecutive 1s). Each octet of message
data (i.e., between flag sequences), following stuffed-zero removal (i.e., discarding a 0
directly following five contiguous 1s), is stored in a FIFO byte. A transition from
zero-stuffed data back to flag sequence marks the end of the message and results in an
interrupt with the indication message received.
If the number of data bits collected is not divisible by eight, or if FCS checking is
enabled and the FCS is incorrect, a type b block is marked in the block type field of
the data block’s status byte (the first byte of the block), the error type is noted in the
same byte, all the data bytes are discarded, and a new block is started on the byte
following the current status byte. Otherwise, a type a1 block is marked, the block
length in the status byte is set to the number of data octets stored, and a new block is
started on the byte following the last data byte stored.
Because consecutive messages can share the flag between them, the next message can
start as soon as new zero-stuffed data is detected, regardless of the number of flags
between the messages.
A sequence of five 1s not followed by 0 (i.e., 01111101111110) is faulty and produces
a type b block (with alignment error-type).
Aborted Message
A transition from zero-stuffed data to abort sequence ( 7 consecutive 1s) marks an
aborted message and results in an interrupt with the indication message received. A
type b block is marked in the block type field, the error type is noted in the same byte,
all the data bytes are discarded, and a new block is started on the byte following the
current status byte. The next message starts only after at least one flag sequence is
located and new zero-stuffed data follows.
Near-Full FIFO Event
A Near-Full FIFO event occurs when the number of bytes in the FIFO buffer is equal
to or more than the Near-Full FIFO threshold and the FIFO near-full interrupt is off
NOTE:
NOTE:
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For each message, all octets between the initial and terminal flags—not including the
flags but including the FCS—are placed in the FIFO buffer.
Two flags with a shared zero between them are treated as two valid flags.
Functional Description
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