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The correct logic analyzer sample position for the data valid windows is just to the left of
(before) the analyzer clock. This ensures that the data being sent by the controller prior
to issuing the strobe is the data sampled by the analyzer. Before moving on to step 3
the sample positions for all data lines should be moved to the left of the clock.
This can be done by grabbing the blue lines on the right side of the clock and dragging
them to the left into the proper data valid window. You can grab any of the blue lines on
the “stack of channels” or “bus composite” views and all of the sample positions for that
label will be adjusted. If a portion of another data valid window appears at the far left of
the display and a blue line moves into that window, you can move it to the proper
window by expanding the display (as described previously) for the appropriate label and
moving the blue line just for the offending signal. After placing the blue lines in the
proper data valid window, select the “Results ->Set Sample Position to Eye Finder
Suggestions” menu pick, and the sample positions will be precisely centered on the
proper data valid window for each channel. Since the ECC bits and data mask signals
have the same timing as the data lines, their sample positions can be adjusted in a
similar way. You can then compress the display if you like.
Setting the sample position for the strobes to the data valid window at the center of the
display will cause them to be sampled just after the active edge that caused data to be
sampled. Thus, the first transfer of a burst will always show a strobe value of 1, and the
last will show a strobe value of 0. This is necessary since for read cycles the strobes
are delayed enough that the sample position adjustment range of the analyzer may not
be sufficient to sample them before the active edge of the strobe. The sampling strategy
for read and write cycles should be consistent to produce consistent output from the
analyzer. This does however mean that Data will be sampled before the clock and
strobes after the clock (the DataClk signal itself should be sampled before the clock.).