ppfg - PulsePins Function Generator

ppfg is a simple "function generator" for binary signals.

Command line switches:

  • -period: time period (floating point value); the unit can be specified attached to the number with no space (accepted suffixes are: ns; us; ms; s=sec=secs; min; h=hr=hrs; d=day=days, u stands for micro, case insensitive; for example 20ms), default unit is seconds; no default value
  • -freq: frequency (floating point value); the unit can be specified attached to the number with no space (accepted suffixes are: uHz, mHz, Hz, kHz, MHz, GHz, u stands for micro, case insensitive except for m/M; for example 5MHz), default unit is Hz; no default value
  • -duty: duty cycle as a percentage of the 'on' signal; fractional values are allowed (floating point); default value is 50
  • -servo: angle setting for testing servo motors using pulse-width modulation (PWM); the angle argument is required when the switch is used
  • -v0: output pattern for low state (default: 0x00000000)
  • -v1: output pattern for high state (default: 0xFFFFFFFF)
  • -start0: set the first pattern presented on the output to the low state (instead of high state; default: off)
  • -delay: delay after trigger before generating the output sequence (in seconds, same syntax as for period; default: 0)
  • -p: trigger pattern (default: 0b00000001)
  • -m: trigger mask (default: 0b00000001)
  • -i: initial output value before triggering (default: 0)
  • -trig, -autotrig: do not wait for external trigger, automatically start (default: off)
  • -gate: gate settings, specified by a gate string (default: disabled)
  • -gate_debug: start the program in gate debug mode; gate signal state is dumped every 100ms (default: off)
  • -core_pll, -core_pll_charge_pump, -core_pll_bandwidth: core-clock PLL settings, as explained here
  • -int_pll, -int_pll_charge_pump, -int_pll_bandwidth: internal streamer-clock PLL settings, as explained here

Specify one positive waveform timing source with -period or -freq; these two options are mutually exclusive. In servo mode, -servo supplies the pulse width from the requested angle. If neither -period nor -freq is supplied, servo mode uses the standard 20 ms / 50 Hz servo PWM period. If -period or -freq is supplied together with -servo, that explicit timing is used and the duty cycle is recomputed to preserve the servo pulse width.

There are two modes of operation, burst mode and continuous mode.

Gate settings

The gating can be enabled through a specification in a 'gate string': -gate en:gate_in_en:mask.

  • en: enable is a boolean (t=T=1, f=F=0)
  • gate_in_en: enable dedicated gate input (gate_in)
  • mask: trigger mask (default: 0b00000000); signals on the trigger port can also be used to enable gate

Burst mode

Activated with -burst N. The parameters are:

  • -burst: number of pulse repetitions after activation; the argument is required when burst mode is used
  • -t: final value (default: 0)
  • -n_max: maximum number of bursts (default: 1; 0 means infinity)

Continuous mode

Activated with -cont (default: off).

Servo motors

As a convenience, using the -servo switch, ppfg can generate an appropriate pulse-width modulation signal for testing servo motors.

By default, -servo uses a 20 ms / 50 Hz PWM period and maps angles from 0 to 180 degrees onto 1 ms to 2 ms high pulses. For example, -servo 90 produces a 1.5 ms high pulse, i.e. 7.5% duty cycle at the default 20 ms period.

If -period or -freq is also supplied, ppfg keeps the servo pulse width and applies it to the explicit period. For example, -servo 90 -freq 100Hz uses a 10 ms period with the same 1.5 ms high pulse, i.e. 15% duty cycle.

In servo mode the duty cycle is derived from the angle, so -duty is ignored.