/usr/share/doc/libcomedi-dev/demo/antialias.c is in libcomedi-dev 0.8.1-5ubuntu6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 | /*
* Antialiasing Analog Output Demo
* Part of Comedilib
*
* Copyright (c) 1999,2000 David A. Schleef <ds@schleef.org>
*
* This file may be freely modified, distributed, and combined with
* other software, as long as proper attribution is given in the
* source code.
*/
/* Not functional */
/*
* Requirements: an analog output subdevice that is capable
* of ansynchronous output.
*
* Normally, the resolution of analog output channels is limited by
* the resolution of the D/A converter. However, if you limit the
* bandwith of the D/A converter by using a low-pass filter, you
* can trade some of the bandwidth for additional resolution. This
* is done by changing the output rapidly between two adjacent
* values: a signal of an alternating 0,1,0,1,0,1 sequence will
* look like 0.5 after an appropriate low-pass filter.
*
* The disadvantage, of course, is that you lose bandwidth. Worse,
* the simple technique demonstrated here will cause predictable
* noise in the stop band. More complicated techniques will allow
* you to tune the spectrum of the noise in the stop band.
*/
#include <stdio.h>
#include <comedilib.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <getopt.h>
#include <ctype.h>
#include "examples.h"
void ao_antialias(unsigned int data);
comedi_t *device;
int main(int argc, char *argv[])
{
lsampl_t data;
int ret;
struct parsed_options options;
init_parsed_options(&options);
parse_options(&options, argc, argv);
device = comedi_open(options.filename);
if(!device){
comedi_perror(options.filename);
exit(0);
}
data = options.value;
if(options.verbose){
printf("writing %d to device=%s subdevice=%d channel=%d range=%d analog reference=%d\n",
data, options.filename, options.subdevice, options.channel, options.range, options.aref);
}
ret = comedi_data_write(device, options.subdevice, options.channel, options.range, options.aref, data);
if(ret<0){
comedi_perror(options.filename);
exit(0);
}
printf("%d\n", data);
ao_antialias((1000<<16)+1000);
return 0;
}
void ao_antialias(unsigned int data)
{
unsigned int hibits=data>>16;
unsigned int lobits=data&0xffff;
int i;
unsigned int acc;
acc=0;
for(i=0;i<100;i++){
acc+=lobits;
printf("%d\n",hibits+(acc>>16));
acc&=0xffff;
}
}
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