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= Pico Drivers
[[cha:pico-drivers]] (((Pico PPMC Driver)))
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 board. The driver is named hal_ppmc.ko
The analog servo interface is also called the PPMC for Parallel Port Motion
Control. There is also the Universal Stepper Controller, abbreviated the
USC. And the Universal PWM Controller, or UPC.
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 useful debugging messages 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 (or
possibly 16 PPMC) devices on it.
== Pins
In the following pins, parameters, and functions, <port> is the parallel
port ID. According to the naming conventions the first port should always
have an ID of zero. All the boards have some method of setting the
address on the EPP bus. USC and UPC have simple provisions for only
two addresses, but jumper foil cuts allow up to 4 boards to be addressed.
The PPMC boards have 16 possible addresses. In all cases, the driver
enumerates the boards by type and exports the appropriate HAL pins.
For instance, the encoders will be enumerated from zero up, in the
same order as the address switches on the board specify. So, the first
board will have encoders 0 -- 3, the second board would have encoders
4 -- 7.
The first column after the bullet tells which boards will have this
HAL pin or parameter associated with it. All means that this pin is
available on all three board types. Option means that this pin
will only be exported when that option is enabled by an optional
parameter in the loadrt HAL command. These options require the
board to have a sufficient revision level to support the feature.
* '(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.
* '(PPMC float output) ppmc.<port>.DAC.<channel>.value' - sends a
signed value to the 16-bit Digital to Analog Converter on the PPMC DAC16
board commanding the analog output voltage of that DAC channel.
* '(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>.din.<channel>.in' - State of digital
input pin, see canonical digital input.
* '(All bit output) ppmc.<port>.din.<channel>.in-not' - Inverted
state of digital input pin, see canonical digital input.
* '(All bit input) ppmc.<port>.dout.<channel>.out' - Value to be
written to digital output, see 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 corresponds 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 or UPC
board. extradac and extradout are mutually exclusive features as they
use the same signal lines for different purposes. These output pins
will be enumerated after the standard digital outputs of the board.
== 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.
* '(PPMC float) ppmc.<port>.DAC.<channel>.scale' - Sets scale
of DAC16 output channel such that an output value equal to the 1/scale
value will produce an output of + or - value Volts. So, if the scale
parameter is 0.1 and you send a value of 0.5, the output will be 5.0 Volts.
* '(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 step 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 step 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.
Applies to a group of four consecutive step generators, as indicated by
'<channel-range>'. The maximum step rate is:
image:images/pico-ppmc-math.png[]
* '(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 value 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>.dout.<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.
== 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 writes are organized into blocks of contiguous registers to be
written in a block to minimize CPU overhead.
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