Pico PPMC

Pico Systems has a family of boards for doing analog servo, stepper, and pwm (digital) servo control. The boards connect to the PC through a parallel port working in EPP mode. Although most users connect one board to a parallel port, in theory any mix of up to 8 or 16 boards can be used on a single parport. One driver serves all types of boards. The final mix of I/O depends on the connected board(s). The driver doesn’t distinguish between boards, it simply numbers I/O channels (encoders, etc) starting from 0 on the first card.

Installing:

loadrt hal_ppmc port_addr=<addr1>[,<addr2>[,<addr3>...]]

The port_addr parameter tells the driver what parallel port(s) to check. By default, <addr1> is 0x0378, and <addr2> and following are not used. The driver searches the entire address space of the enhanced parallel port(s) at port_addr , looking for any board(s) in the PPMC family. It then exports HAL pins for whatever it finds. During loading (or attempted loading) the driver prints some usefull debugging message to the kernel log, which can be viewed with dmesg.

Up to 3 parport busses may be used, and each bus may have up to 8 devices on it.

0.1. Pins

In the following pins, parameters, and functions, <board> is the board ID. According to the naming conventions the first board should always have an ID of zero. However this driver sets the ID based on switches on the board, so it may be non-zero even if there is only one board.

(All s32` output) ppmc.<port>.encoder.<channel>.count` — Encoder position, in counts.
(All s32` output) ppmc.<port>.encoder.<channel>.delta` — Change in counts since last read, in raw encoder count units.
(All float output) ppmc.<port>.encoder.<channel>.velocity — Velocity scaled in user units per second. On PPMC and USC this is derived from raw encoder counts per servo period, and hence is affected by encoder granularity. On UPC boards with the 8/21/09 and later firmware, velocity estimation by timestamping encoder counts can be used to improve the smoothness of this velocity output. This can be fed to the pid hal component to produce a more stable servo response. This function has to be enabled in the hal command line that starts the ppmc driver, with the timestamp=0x00 option.
(All float` output) ppmc.<port>.encoder.<channel>.position` — Encoder position, in user units.
(All bit ``bidir) ``ppmc.<port>.encoder.<channel>.index-enable — Connect to axis.#.index-enable for home-to-index. This is a bidirectional hal signal. Setting it to true causes the encoder hardware to reset the count to zero on the next encoder index pulse. The driver will detect this and set the signal back to false.
(UPC bit ``input) ``ppmc.<port>.pwm.<channel>.enable — Enables a PWM generator.
(UPC float ``input) ``ppmc.<port>.pwm.<channel>.value — Value which determines the duty cycle of the PWM waveforms. The value is divided by pwm.<channel>.scale , and if the result is 0.6 the duty cycle will be 60%, and so on. Negative values result in the duty cycle being based on the absolute value, and the direction pin is set to indicate negative.
(USC bit ``input) ``ppmc.<port>.stepgen.<channel>.enable — Enables a step pulse generator.
(USC float ``input) ``ppmc.<port>.stepgen.<channel>.velocity — Value which determines the step frequency. The value is multiplied by stepgen.<channel>.scale , and the result is the frequency in steps per second. Negative values result in the frequency being based on the absolute value, and the direction pin is set to indicate negative.
(All bit ``output) ``ppmc.<port>.in-<channel> — State of digital input pin, see canonical digital input.
(All bit ``output) ``ppmc.<port>.in.<channel>-not — Inverted state of digital input pin, see canonical digital input.
(All bit ``input) ``ppmc.<port>.out-<channel> — Value to be written to digital output, seen canonical digital output.
(Option float input) ppmc.<port>.DAC8-<channel>.value — Value to be written to analog output, range from 0 to 255. This sends 8 output bits to J8, which should have a Spindle DAC board connected to it. 0 correponds to zero Volts, 255 corresponds to 10 Volts. The polarity of the output can be set for always minus, always plus, or can be controlled by the state of SSR1 (plus when on) and SSR2 (minus when on). You must specify extradac = 0x00 on the hal command line that loads the ppmc driver to enable this function on the first USC ur UPC board.
(Option bit input) ppmc.<port>.dout-<channel>.out — Value to be written to one of the 8 extra digital output pins on J8. You must specify extradout = 0x00 on the hal command line that loads the ppmc driver to enable this function on the first USC ur UPC board. extradac and extradout are mutually exclusive features as they use the same signal lines for different purposes.

0.2. Parameters

(All float) ``ppmc.<port>.enc.<channel>.scale — The number of counts / user unit (to convert from counts to units).
(UPC float) ``ppmc.<port>.pwm.<channel-range>.freq — The PWM carrier frequency, in Hz. Applies to a group of four consecutive PWM generators, as indicated by <channel-range>. Minimum is 610Hz, maximum is 500KHz.
(UPC float) ppmc.<port>.pwm.<channel>.scale — Scaling for PWM generator. If scale is X, then the duty cycle will be 100% when the value pin is X (or -X).
(UPC float) ppmc.<port>.pwm.<channel>.max-dc — Maximum duty cycle, from 0.0 to 1.0.
(UPC float) ppmc.<port>.pwm.<channel>.min-dc — Minimum duty cycle, from 0.0 to 1.0.
(UPC float) ppmc.<port>.pwm.<channel>.duty-cycle — Actual duty cycle (used mostly for troubleshooting.)
(UPC bit) ppmc.<port>.pwm.<channel>.bootstrap — If true, the PWM generator will generate a short sequence of pulses of both polarities when E-stop goes false, to charge the bootstrap capacitors used on some MOSFET gate drivers.
(USC u32) ppmc.<port>.stepgen.<channel-range>.setup-time — Sets minimum time between direction change and step pulse, in units of 100nS. Applies to a group of four consecutive PWM generators, as indicated by <channel-range>.
(USC u32) ppmc.<port>.stepgen.<channel-range>.pulse-width — Sets width of step pulses, in units of 100nS. Applies to a group of four consecutive PWM generators, as indicated by <channel-range>.
(USC u32) ppmc.<port>.stepgen.<channel-range>.pulse-space-min — Sets minimum time between pulses, in units of 100nS. The maximum step rate is 1/( 100nS * ( pulse-width + pulse-space-min )). Applies to a group of four consecutive PWM generators, as indicated by <channel-range>.
(USC float) ppmc.<port>.stepgen.<channel>.scale — Scaling for step pulse generator. The step frequency in Hz is the absolute value of velocity * scale.
(USC float) ppmc.<port>.stepgen.<channel>.max-vel — The maximum value for velocity. Commands greater than max-vel will be clamped. Also applies to negative values. (The absolute value is clamped.)
(USC float) ppmc.<port>.stepgen.<channel>.frequency — Actual step pulse frequency in Hz (used mostly for troubleshooting.)
(Option float) ppmc.<port>.DAC8.<channel>.scale — Sets scale of extra DAC output such that an output velue equal to scale gives a magnitude of 10.0 V output. (The sign of the output is set by jumpers and/or other digital outputs.)
(Option bit) ppmc.<port>.out.<channel>-invert — Inverts a digital output, see canonical digital output.
(Option bit) ppmc.<port>.dout.<channel>-invert — Inverts a digital output pin of J8, see canonical digital output.

0.3. Functions

(All funct) ``ppmc.<port>.read — Reads all inputs (digital inputs and encoder counters) on one port. These reads are organized into blocks of contiguous registers to be read in a block to minimize CPU overhead.
(All funct) ``ppmc.<port>.write — Writes all outputs (digital outputs, stepgens, PWMs) on one port. These reads are organized into blocks of contiguous registers to be read in a block to minimize CPU overhead.