AN2577 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'AN2577' PDF : 34 Pages View PDF
eTPU software design
AN2577
// Setup match event to block out input trans too close to
the valid falling edge.
// The transition detection is disabled until the match event
on the action unit A occur.
SetupMatch_A((EdgeCaptureTime + ToothPeriod*BlankingRatio),
Mtcr1_Ctcr1_ge, match_no_change);
4.2.3
4.2.4
// Setup match event to detect stall condition
// If the crank edge transition does not occur again for a
StallPeriod, it is stalled
SetupMatch_B((EdgeCaptureTime + StallPeriod),
Mtcr1_Ctcr1_ge, match_no_change);
} // active edge
First period
When the second edge is detected, the function can make the first measurement of the
tooth period. The period should be stored as a global variable, as it is the best measure of
the wheel speed and may be used by other drivers. Before it is overwritten, the previous
period should be stored off for use in detecting the gap.
Testing for a possible gap
When the third edge is detected, enough information finally exists to test for the missing
tooth gap. This routine is now the default for subsequent teeth. This state is repeated until
the gap test is satisfied after which a confirming test needs to performed on the following
period.
It is necessary from this point on to count the teeth that are detected. For example, if a 36-1
tooth wheel produces more than 35 tooth periods without a gap detection, an exception
might be raised with the host. Typically the tooth count is rectified when the first gap is
detected. After that, the software can anticipate subsequent gap detections.
If the wheel is to be tracked over 720 degrees as is necessary for a four cycle automotive
engine, a separate search needs to be conducted for the unique cam information indicating
which of the two crankshaft cycles are currently being tracked. Note that the cam
information and the crank synchronization are both needed to determine full
synchronization.
In addition to tracking the tooth period and count, the angle clock software should provide
status to the host and other applications using the angle information. The status selections
might include:
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