HyCon - Hybrid controller for analog computers
This document refers to version 0.1 of HyCon
use strict;
use warnings;
use File::Basename;
use HyCon;
(my $config_filename = basename($0)) =~ s/\.pl$//;
print "Create object...\n";
my $ac = HyCon->new("$config_filename.yml");
$ac->set_ic_time(500); # Set IC-time to 500 ms
$ac->set_op_time(1000); # Set OP-Time to 1000 ms
$ac->single_run(); # Perform a single computation run
my $result = $ac->read_analog(); # Read values from the analog computer
This module implements a simple interface to the a hybrid controller which interfaces an analog computer to a digital computer and thus allows true hybrid computation.
This function generates a HyCon-object. Currently there is only one hybrid controller supported, so this is, in fact, a singleton and every subsequent invocation will cause a fatal error. This function expects a path to a YAML configuration file of the following structure:
config.yml:
serial:
port: /dev/tty.usbmodem621
bits: 8
baud: 115200
parity: none
stopbits: 1
poll_interval: 1000
poll_attempts: 50
calibration:
analog_in:
- 523, 120, 830
- 523, 119, 830
- 524, 120, 830
- 523, 120, 832
- 523, 120, 830
- 523, 120, 830
The device shown in the following example will not fit your particular configuration, it is just an example. The remaining parameters nevertheless apply in general and are mostly self-explanatory. poll_interval and poll_attempts control how often this interface will poll the hybrid controller to get a response to a command. The values shown above are overly pessimistic but won't hurt during normal operation.
The calibration section of the configuration file holds calibration data for the analog-digital converter and its associated level shifters of the hybrid controller. There is one line for each AD-channel. The first entry in each line describes the value read when the respective input is held at 0. The two following values represent the AD-readout when fed with -1 and +1 respectively. If this section is missing, defaults will be used which will yield unscaled/unshifted values from the analog-digital converter.
The new() function will clear the communication buffer of the hybrid controller by reading and discarding and data until a timeout will be reached. This is currently ten times as long as the product of poll_interval and poll_attempts, so the settings shown above will result in a 500 ms delay of the new() function.
In some cases, e.g. external HALT conditions, it is necessary to query the hybrid controller for any messages which may have occured since the last command. This can be done with this method - it will poll the controller for a period of poll_interval times poll_attemps microseconds.
This method switches the analog computer to IC (initial condition) mode during which the integrators are (re)set to their respective initial value. Since this involves charging a capacitor to a given value, this mode should be activated for the right duration as required by the analog computer being controlled. Especially on historic machines it is not uncommon to have IC-durations of up to a second when a given computer setup includes integrators set to time constant 1. Refer to the analog computer's documentation for detailed information on setup times.
ic() and the two following methods should not be used normally when timing is critical. Instead, IC- and OP-times should be setup explicitly (see below) and then a single-run should be initiated which will be under control of the hybrid controller which takes care for sub-millisecond precision with respect to timing issues.
This method switches the analog computer to OPerating-mode.
Calling this method causes the analog computer to switch to HALT-mode. In this mode the integrators are halted and store their last value. After calling halt() it is possible to return to OP-mode by calling op() again. Depending on the analog computer being controlled, there will be a more or less substantial drift of the integrators in HALT-mode, so it is advisable to keep the HALT-periods as short as possible to minimize errors.
A typical operation cycle may look like this: IC-OP-HALT-OP-HALT-OP-HALT. This would start a single computation with the possibility of reading values from the analog computer during the HALT-intervals.
Another typical cycle is called "repetitive operation" and looks like this: IC-OP-IC-OP-IC-OP... This is normally used with the integrators set to fast time-constants and allows to display a solution as a more or less flicker free curve on an oscilloscope for example.
During a normal computation on an analog computation there should be no overloads of summers or integrators. Such overload conditions are either a sign of a machine failure or (more common) an erroneous computer setup (normally caused by wrong scaling of the underlying equations). To catch such problems it is usually a good idea to switch the analog computer automatically to HALT-mode when an overload occurs. This is done by calling this method during the setup phase.
Calling this method will disable the automatic halt-on-overload functionality of the hybrid controller.
Sometimes it is necessary to halt a computation when some condition is fulfilled (some value reached etc.). This is normally detected by a comparator used in the analog computer setup. The hybrid controller features an EXT-HALT input jack that can be connected to such a comparator. After calling this method, the hybrid controller will switch the analog computer from OP-mode to HALT as soon as the input signal patched to this input jack goes high.
This method disables the HALT-on-overflow feature of the hybrid controller.
Calling this method will initiate a so-called "single-run" on the analog computer which automatically performs the sequence IC-OP-HALT. The times spent in IC- and OP-mode are specified with the methods set_ic_time() and set_op_time() (see below).
It should be noted that the hybrid controller will not be blocked during such a single-run - it is still possible to issue other commands to read or set ports etc.
This initiates repetitive operation, i.e. the analog computer is commanded to perform an IC-OP-IC-OP-... sequence. The hybrid controller will also not block during this run. To terminate a repetitive run, either ic() or halt() may be called, depending on the mode the analog computer should stop. Note that these methods act immediately and will interrupt any ongoing IC- or OP-period of the analog computer.
It is normally advisable to let the hybrid controller take care of timing the analog computer modes of operation. This method sets the time the analog computer will spend in IC-mode during a single- or repetitive run. The time is specified in milliseconds and must be positive and can not exceed 999999 milliseconds due to limitations of the hybrid controller itself.
This method specifies the duration of the OP-cycle(s) during a single- or repetitive analog computer run. The same limitations hold with respect to the time specified as for the set_ic_time() method.
The hybrid controller features a number (six) of analog inputs which can be read by calling this method. It returns a reference to an array of floats which represent the value supplied by the analog computer to the respective analog-converter input. The scaling is done based on the data supplied in the calibration-analog_in-section of the YAML-configuration file.
It should be noted that while the normal range of variables in a computer setup is between -1 and +1 (typically represented by +/-10 V), the hybrid controller maps the full +/-15 V range to the permissible 0-5 V input range of the analog-digital converter. This is necessary to avoid damage to the hybrid controller in case of an overlowed variable, thus diminishing the 12 bit resolution.
In addition to the analog input channels mentioned above, the hybrid controller also features digital inputs (two) which can be used to read out the state of comparators or other logic elements of the analog computer being controlled. This method also returns an array-reference containing values of 0 or 1.
The hybrid controller also features digital outputs (two) which can be used to control electronic/relay switches in the analog computer being controlled. Calling digital_output(0, 1) will set the first (0) digital output to 1 etc.
Calling get_status() yields a reference to a hash containing all current status information of the hybrid controller. A typical hash structure returned may look like this:
$VAR1 = {
'IC-time' => '500',
'MODE' => 'HALT',
'OP-time' => '1000',
'STATE' => 'NORM',
'OVLH' => 'DIS',
'EXTH' => 'DIS'
};
In this case the IC-time has been set to 500 ms while the OP-time is set to one second. The analog computer is currently in HALT-mode, and the hybrid controller is in its normal state, i.e. it is not currently performing a single- or repetitive-run. HALT on overload and external HALT are both disabled.
In some applications it is useful to be able to determine how long the analog computer has been in OP-mode. As time as such is the only so-called free variable of integration in an analog-electronic analog computer, it is a central parameter to know. Imagine that some integration is being performed by the analog computer and the time which it took to reach some threshold value is being investigated. In this case, the hybrid controller would be configured so that external-HALT is enabled. Then the analog computer would be placed to IC-mode and then to OP-mode. After an external HALT has been triggered by some comparator of the analog commputer, the hybrid controller with switch the analog computer to HALT-mode immediately. Afterwards, the time the analog computer spent in OP-mode can be determined by calling this method. The time will be returned in microseconds (the resolution should be +/- 3 to 4 microseconds).
Dr. Bernd Ulmann <ulmann@analogparadigm.com>