GS6151 Datasheet, PDF (40/77 Pages) Semtech Corporation – Multi-Rate 6G UHD-SDI

4.12 Diagnostic Features
To aid in debug, the GS6151 has an on-chip eye monitoring, error counting and
PRBS-signal generation features that can be used to check system links for error-free
operation. The PRBS signal generator outputs a PRBS7 bit stream (x⁷+x⁶+1 polynomial)
or clock (at the reference or divided rates) which can be clocked from either an on-chip
or off-chip source. The eye monitor is a 128-bit horizontal eye monitor (HEM) that can
automatically detect the error-free eye width, the first error-free phase position and
provide a bitmap of the error status of each phase without affecting the retiming
capability of the CDR. Additionally, the HEM can be configured to manually count the
number of errors at a given phase for a given time interval or to continually count errors
until programmed to stop. In any of these three modes, described in the next section,
Section 4.12.1, the criteria for measuring a bit error can also be set to measure bit errors
of arbitrary data (in which the input to the CDR is assumed to be BER-free at some phase)
or by checking against a PRBS7 bit stream for measuring error-free performance of
upstream devices. PRBS checking is described in Section 4.12.2. The PRBS generator is
described in Section 4.12.3. The HEM and PRBSCHK features operate at 3Gb/s and HD
data rates, while the PRBS generator operates at 3G, HD, SD and MADI rates.
4.12.1 Horizontal Eye Monitor Modes
The three modes of bit error characterization of the HEM are described below. In this
section it is assumed that arbitrary data is being input and checked. For each of these
modes (and the PRBS7 input data checking mode in section 4.12.3) the Horizontal Eye
Monitor must be enabled by setting the HORIZONTAL_EYE_MON_ENABLE bit of the
EYE_MON_ENABLE register at address 23_h.
4.12.1.1 Automatic Eye Scan
The automatic eye-scan mode measures the error-free eye width and first error-free
phase (EYE_WIDTH and STARTING_PHASE bits, respectively, of
EYE_MON_STATUS_REG_2) position as well as the resultant error bitmap of each of the
128 phases (EYE_BITMAP bits of EYE_MON_STATUS_REG_4 to
EYE_MON_STATUS_REG_11, least-significant bits correspond to leftmost bits). A bit
value of 1 in the bitmap indicates error-free operation at the phase that corresponds to
the bit. A bit value of 0 indicates more than the ERROR_THRESHOLD number of errors
have been counted and the bit is considered as an error bit. It should be noted that the
eye is not necessarily centered in the results, i.e. the crossing may be in the center of the
bitmap and the open eye can wrap around from phase 127 back to 0. The automatic eye
scan takes this into account and calculates the value for the error-free eye across the
wrapping while the error-free phase corresponds to the leftmost portion of the
error-free eye rather than the leftmost error-free phase in the bitmap. Refer to
Figure 4-22 below.
GS6151
Final Data Sheet
PDS-060389
Rev.4
August 2015
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