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TMXF28155 Super Mapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
Preliminary Data Sheet, Rev. 1
October 2000
344
Lucent Technologies Inc.
M13/M23 Mux/Demux Block Functional Description
(continued)
M13/M23 Demultiplexer
(continued)
FIFO Usage.
The FIFO is large enough to hold one full and two partial standard DS3 LAPD frames of 79 bytes. In
case shorter frames are being transmitted, the M13 can keep track of up to four frames in the FIFO that have not
been read.
The receive data-link frame interrupt bit, M13_RDL_FRM_INT (Table 218), is set when a frame closing flag or an
abort byte is received. The M13_RDL_FIFO_UF (Table 226) bit is set if the buffer underflows and the
M13_RDL_FIFO_AF (Table 226) bit is set if the buffer reaches a provisionable fill level. The fill level can be set to
16 bytes (M13_RDL_FILL[1:0] = 00 (Table 288)), 32 bytes (M13_RDL_FILL[1:0] = 01), 64 bytes
(M13_RDL_FILL[1:0] = 10), or 96 bytes (M13_RDL_FILL[1:0] = 11).
The user may read bytes from the FIFO through register M13_RDL_DATA_R (Table 255). The portion of the earli-
est frame still in the FIFO can be deleted by setting M13_RDL_FRM_CLR (Table 259) to 1. (This is normally done
to purge a corrupted or aborted frame.) The user must reset M13_RDL_FRM_CLR before another frame can be
deleted. If M13_RDL_FRM_CLR is set before the closing flag of the frame currently being read from the FIFO has
been received, all subsequent bytes of the frame will be discarded without being written into the FIFO.
Frame Status and Error Reporting.
The M13 provides information on the earliest frame still in the FIFO through
status register M13_RHDLC_STATUS_R (Table 257).
The status register has 1 bit to indicate whether or not the closing flag (or an abort byte) for the current frame has
been received, 1 bit to indicate if the current frame is corrupted, 5 bits to indicate the size of the current frame mod-
ulo-32, and 1 bit to indicate whether or not there are less than 32 bytes of the earliest frame left in the FIFO.
There are 4 ways in which the M13 can identify that the current frame has been corrupted. The frame may have
been aborted (M13_RDL_ABORT = 1 (Table 254)), it may have failed the CRC check (M13_RDL_FCS_ERR =
1(Table 254)), the number of bits between opening and closing flags may not have been a multiple of 8
(M13_RDL_NOT_BYTE = 1 (Table 254)), or it may have been overwritten before being read from the FIFO
(M13_RDL_OVFL = 1 (Table 254)). Also, there is a separate bit M13_RDL_FLAG (Table 254) to indicate whether or
not the closing flag (or an abort byte) for the current frame has been received.
The size of the current frame modulo-128 (including FCS bytes only if M13_RDL_FCS = 0 (Table 288)) is indicated
by register M13_RDL_FRAME_SIZE_R (Table 256).
DS3 Performance Monitors.
For performance monitoring purposes, there are a number of error counters in the
M13. All of these internal counters are comprised of a running error counter and a hold register that presents stable
results to the microprocessor. The counts in all of the running counters are latched to the hold registers and the
running counters cleared with the configured internal performance monitor reset signal.
The latched results are then held to be read by the microprocessor. All of the internal counters have the ability to
store more than the maximum possible count in a one second interval for a bit error rate of 10
-3
. As long as the per-
formance monitor reset occurs at least once every second, no counts will be lost. In case this doesn’t happen, all of
the running counters will either hold their maximum value or roll over to zero depending on the control signal input
SMPR_SAT_ROLLOVER (Table 15).
Within the M23 demultiplexer, there are 4 performance monitoring counters. M13_DS3_FERR_CNT[11:0]
(Table 290) increments each time an error is detected in either an F bit or M bit, and M13_DS3_PERR_CNT[13:0]
(Table 293) increments if at least one of the P bits disagrees with the parity of the previous frame. In the C-bit parity
mode only, M13_DS3_CPERR_CNT[13:0] (Table 292) counts frames with at least two of the three C-bit parity bits
indicating an error, and M13_DS3_FEBE_CNT[13:0] (Table 291) accumulates FEBE error indications (1 error indi-
cation for each DS3 frame with at least one FEBE bit equal to zero).