.TH E1432_SET_TACH_PPR 3 E1432
.SH NAME
.nf
e1432_set_tach_ppr \- Set tach pulses per revolution
e1432_get_tach_ppr \- Get tach pulses per revolution
.fi
.IX e1432_set_tach_ppr(3) 3
.IX e1432_get_tach_ppr(3) 3
.SH SYNOPSIS
.cS
SHORTSIZ16 e1432_set_tach_ppr(E1432ID hw, SHORTSIZ16 ID,
                              FLOATSIZ32 tach_ppr)
SHORTSIZ16 e1432_get_tach_ppr(E1432ID hw, SHORTSIZ16 ID,
                              FLOATSIZ32 *tach_ppr)
.cE
.SH DESCRIPTION

\fIe1432_set_tach_ppr\fR sets the number of tachometer pulses per revolution, 
of a single channel or group of channels \fIID\fR, 
to the value given in \fItach_ppr\fR.

\fIe1432_get_tach_ppr\fR returns the current value of the tach
pulses per revolution, of a single channel or group of channels \fIID\fR,
into a memory location pointed to by \fItach_ppr\fR.

\fIhw\fR must be the result of a successful call to
\fIe1432_assign_channel_numbers\fR, and specifies the group of
hardware to talk to.

\fIID\fR is either the ID of a group of channels that was obtained
with a call to \fIe1432_create_channel_group\fR, or the ID of a single
channel.

\fItach_ppr\fR is the tach pulses per revolution.  

For input channels and source channels, this parameter is not used.

\fINote\fR: The E1432/3/4 tachometer inputs have a bandwidth of
100kHz, representing 8333 RPM at 720 PPR.  However, this 100kHz rate
will not be usable in many circumstances.

The E1432/3/4 order-tracking algorithm for resampling time data has no
theoretical limits on maximum ppr.  There are, however, practical
limits as a result of available processing power; order-tracking is a
very computationally intensive algorithm.  Settings of 0.5 to 4 for
\fItach_ppr\fR seem optimal for most applications.  If the DUT is
producing more than 4 PPR, it is possible to reduce the amount of tach
processing required with the aid of the \fIe1432_set_tach_decimate\fR
function.

When the resample mode (as set by \fIe1432_set_sample_mode\fR) is set
to \fBE1432_RESAMP_AT_TACH\fR, the order tracking algorithm used is
less computationally intensive.  This should increase the practical
limit on \fItach_ppr\fR somewhat.

The best way to determine what these practical limitations are is by
experimentation.  Factors that affect this processing include ppr,
channel count, module count, block size, sample rate, amount of DRAM
available, and device RPM.  System aspects which may have an affect
include the host interface hardware, the host, and programming
environment.

.SH "RESET VALUE"
After a reset, the \fItach_ppr\fR is set to 1.
.SH "RETURN VALUE"
Return 0 if successful, a (negative) error number otherwise.
.SH "SEE ALSO"
.na
e1432_get_tach_ppr_limits, e1432_set_sample_mode,
e1432_set_tach_decimate
.ad
