a4dd004076
Report the seconds and microseconds values from the INSN_GTOD instructions as unsigned values to postpone the Y2038 problem to a Y2106 problem. Be a bit more careful with the conversion to a signed difference. We wouldn't normally expect time to go backwards, but it is possible if the system time is set to to an older time between the instructions. Also, in the description of INSN_GTOD in the Comedilib manual, explicitly mention that the seconds and microseconds values are unsigned.
127 lines
3.3 KiB
C
127 lines
3.3 KiB
C
/*
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* Instruction example
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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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/*
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This example shows how to use instructions, i.e., comedi_insns.
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Using instructions directly, as in this example, is not recommended
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for the beginner. Use the higher-level functions such as
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comedi_data_read(), comedi_data_write(), etc., as demonstrated
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in the inp, outp, and dio examples. Then, if you need the
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additional flexibility that using instructions directly
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provides, study this example and the implementations of
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comedi_data_read(), etc.
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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 <sys/time.h>
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#include <unistd.h>
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#include "examples.h"
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/*
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* This example does 3 instructions in one system call. It does
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* a gettimeofday() call, then reads N_SAMPLES samples from an
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* analog input, and the another gettimeofday() call.
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*
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* (Note: The gettimeofday() value is obtained using an INSN_GTOD
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* instruction, which places the seconds value in data[0] and the
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* microseconds in data[1], so the seconds value is limited to
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* 32-bits even on 64-bit systems.)
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*/
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#define MAX_SAMPLES 128
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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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int ret,i;
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comedi_insn insn[3];
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comedi_insnlist il;
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lsampl_t t1[2], t2[2];
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lsampl_t data[MAX_SAMPLES];
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long diffus;
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struct parsed_options options;
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init_parsed_options(&options);
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options.n_scan = 10; /* override default n_scan value to something more suitable */
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parse_options(&options, argc, argv);
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if(options.n_scan > MAX_SAMPLES ){
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fprintf( stderr, "Requested too many samples, reducing to %i\n", MAX_SAMPLES );
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options.n_scan = MAX_SAMPLES;
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}
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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(-1);
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}
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if(options.verbose){
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printf("measuring device=%s subdevice=%d channel=%d range=%d analog reference=%d\n",
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options.filename, options.subdevice, options.channel, options.range, options.aref);
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}
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/* Set up a the "instruction list", which is just a pointer
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* to the array of instructions and the number of instructions.
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*/
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il.n_insns=3;
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il.insns=insn;
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/* Instruction 0: perform a gettimeofday() */
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insn[0].insn=INSN_GTOD;
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insn[0].n=2;
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insn[0].data=t1;
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/* Instruction 1: do 10 analog input reads */
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insn[1].insn=INSN_READ;
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insn[1].n = options.n_scan;
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insn[1].data=data;
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insn[1].subdev = options.subdevice;
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insn[1].chanspec=CR_PACK(options.channel, options.range, options.aref);
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/* Instruction 2: perform a gettimeofday() */
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insn[2].insn=INSN_GTOD;
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insn[2].n=2;
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insn[2].data=t2;
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ret=comedi_do_insnlist(device,&il);
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if(ret<0){
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comedi_perror(options.filename);
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exit(-1);
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}
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printf("initial time: %u.%06u\n", t1[0], t1[1]);
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for(i = 0; i < options.n_scan; i++){
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printf("%d\n", data[i]);
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}
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printf("final time: %u.%06u\n", t2[0], t2[1]);
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if (t2[0] >= t1[0]) {
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diffus = (long)(t2[0] - t1[0]);
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} else {
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diffus = -(long)(t1[0] - t2[0]);
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}
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diffus *= 1000000;
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if (t2[1] >= t1[1]) {
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diffus += (long)(t2[1] - t1[1]);
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} else {
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diffus -= (long)(t1[1] - t2[1]);
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}
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printf("difference (us): %ld\n", diffus);
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return 0;
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}
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