Setting The Phase And Servo Clock Period In The Cpu - Delta Tau Power PMAC User Manual

Power PMAC User's Manual
cycles. Saved setup element Sys.ServoPeriod must contain this value in units of milliseconds.
Unless the processor is generating its own interrupts internally, this parameter does not control
the servo update period, it merely notifies the interpolation software what this period is. The
default value of Sys.ServoPeriod matches the default settings for the servo update period in the
Gaten[i] data structures.
Motor[x].Stime: Motor Servo-Loop Closure Extension
It is possible to extend the time between consecutive servo loop closures for an individual motor
by setting Motor[x].Stime to a value greater than 0. The motor skips this many servo interrupt
periods between consecutive loop closures, so closes its loop every (Motor[x].Stime + 1) servo
interrupt periods. This feature is valuable for actuators with very slow dynamics. This is
discussed in more detail in the Setting Up the Servo Loop chapter of the User's Manual.
Sys.RtIntPeriod: Real-Time Interrupt Period
The real-time interrupt (RTI) is the next lower priority after the servo interrupt. The period is an
integer multiple of the servo period – it executes every (Sys.RtIntPeriod + 1) servo periods. At
the default setting, it occurs every third servo period. The main tasks performed in the real-time
interrupt are motion program calculations and foreground PLC (script and C) program
calculations. It also decrements the watchdog timer counter each RTI period, and this must
happen more than 40 times per second to avoid a watchdog timer trip.
Sys.MotorsPerRtInt: Number of Motors Checked per RTI
By default, Power PMAC will perform a safety and status update for each active motor every
real-time interrupt, checking for issues such as overtravel limits, amplifier faults, encoder loss,
and integrated current limits. This checking can often take 0.5 microseconds or more per motor
per RTI.
In applications with very high RTI frequencies, typically for very high move block rates, this
frequency of checking is not needed and can consume a noticeable percentage of CPU time.
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Setting Sys.MotorsPerRtInt (new in V1.6 firmware, released 1 quarter 2014) to a value greater
than 0 means that only the specified number of motors will be checked each RTI. This parameter
provides the user with additional flexibility in allocating CPU time in demanding applications.

Setting the Phase and Servo Clock Period in the CPU

If there are no DSPGATEn ICs in the Power PMAC system to generate system phase and servo
clocks to interrupt the processor, the processor can be set up to generate its own interrupt
internally. This is done by setting saved setup element Sys.CpuTimerIntr to 1. (At the default
value of 0, the processor is expecting to receive external clock signals from an IC.) In this mode,
Sys.ServoPeriod actually sets the period/frequency of the phase and servo updates (which are the
same), rather than just reporting a value to the interpolation routines.
This mode of operation is used when the Power PMAC is commanding servo drives over a
network such as EtherCAT and does not need any local ICs, or for software simulation purposes
when only a CPU is present. Note that the CPU cannot output physical phase and servo clock
signals in this mode, so it could not be kept synchronized with any of these local ICs.
Power PMAC System Configuration 70