add some error checking

diff --git a/demo/ao_waveform.c b/demo/ao_waveform.c
index b78db7719ea51527283db2a5a5b72e90cf58b9c2..364d7622ceeb6bad5772f65fdd39d03f1bbfb0cb 100644 (file)
--- a/demo/ao_waveform.c
+++ b/demo/ao_waveform.c
@@ -117,7 +117,7 @@ int main(int argc, char *argv[])
        parse_options(argc,argv);
 
        /* Force n_chan to be 1 */
-       n_chan = 2;
+       n_chan = 1;
 
        if(value){
                waveform_frequency = value;
@@ -163,6 +163,18 @@ int main(int argc, char *argv[])
 
        dump_cmd(stdout,&cmd);
 
+       err = comedi_command_test(dev, &cmd);
+       if (err < 0) {
+               comedi_perror("comedi_command_test");
+               exit(1);
+       }
+
+       err = comedi_command_test(dev, &cmd);
+       if (err < 0) {
+               comedi_perror("comedi_command_test");
+               exit(1);
+       }
+
        if ((err = comedi_command(dev, &cmd)) < 0) {
                comedi_perror("comedi_command");
                exit(1);