95 lines
2.3 KiB
C
95 lines
2.3 KiB
C
/*
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* Antialiasing Analog Output Demo
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* Part of Comedilib
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*
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* Copyright (c) 1999,2000 David A. Schleef <ds@schleef.org>
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*
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* This file may be freely modified, distributed, and combined with
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* other software, as long as proper attribution is given in the
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* source code.
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*/
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/* Not functional */
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/*
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* Requirements: an analog output subdevice that is capable
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* of ansynchronous output.
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*
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* Normally, the resolution of analog output channels is limited by
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* the resolution of the D/A converter. However, if you limit the
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* bandwith of the D/A converter by using a low-pass filter, you
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* can trade some of the bandwidth for additional resolution. This
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* is done by changing the output rapidly between two adjacent
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* values: a signal of an alternating 0,1,0,1,0,1 sequence will
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* look like 0.5 after an appropriate low-pass filter.
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*
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* The disadvantage, of course, is that you lose bandwidth. Worse,
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* the simple technique demonstrated here will cause predictable
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* noise in the stop band. More complicated techniques will allow
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* you to tune the spectrum of the noise in the stop band.
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*/
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#include <stdio.h>
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#include <comedilib.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <errno.h>
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#include <getopt.h>
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#include <ctype.h>
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#include "examples.h"
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void ao_antialias(unsigned int data);
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comedi_t *device;
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int main(int argc, char *argv[])
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{
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lsampl_t data;
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int ret;
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struct parsed_options options;
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init_parsed_options(&options);
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parse_options(&options, argc, argv);
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device = comedi_open(options.filename);
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if(!device){
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comedi_perror(options.filename);
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exit(0);
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}
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data = options.value;
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if(options.verbose){
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printf("writing %d to device=%s subdevice=%d channel=%d range=%d analog reference=%d\n",
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data, options.filename, options.subdevice, options.channel, options.range, options.aref);
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}
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ret = comedi_data_write(device, options.subdevice, options.channel, options.range, options.aref, data);
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if(ret<0){
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comedi_perror(options.filename);
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exit(0);
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}
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printf("%d\n", data);
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ao_antialias((1000<<16)+1000);
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return 0;
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}
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void ao_antialias(unsigned int data)
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{
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unsigned int hibits=data>>16;
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unsigned int lobits=data&0xffff;
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int i;
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unsigned int acc;
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acc=0;
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for(i=0;i<100;i++){
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acc+=lobits;
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printf("%d\n",hibits+(acc>>16));
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acc&=0xffff;
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}
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}
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