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demo/mmap: support integer wraparound and large sample size

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Currently, the 'front' and 'back' variables are of type 'int' (signed
32-bit integers).  The loop will break when 'front < back', which will
happen when more than 'INT_MAX' bytes of data have been produced.
Redefine them as 'unsigned int' and also allow 'front < back' which will
happen when more than 'UINT_MAX' bytes of data have been produced.
Because the buffer size is not necessarily a power of 2, we can no
longer just use '(back + i) % size' to get the buffer position
corresponding to 'back + i', so introduce a new variable 'bufpos' to
keep track of the buffer position.

Also allow for subdevices that set the 'SDF_LSAMPL' flag to indicate
they use the large (32-bit, 'lsampl_t') sample type instead of the small
(16-bit, 'sampl_t') sample type.

Also, rename the buffer size variable 'size' to 'bufsize'.
This commit is contained in:
Ian Abbott 2015-11-23 16:04:11 +00:00
parent 49f298cf86
commit 65063d785e
1 changed files with 46 additions and 12 deletions
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58
demo/mmap.c
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@ -38,10 +38,15 @@ int main(int argc, char *argv[])
{
comedi_t *dev;
comedi_cmd c,*cmd=&c;
int size;
int front, back;
unsigned int bufsize;
unsigned int front, back;
int ret;
int i;
unsigned int i;
unsigned int bufpos;
unsigned int subdev_flags;
unsigned int sample_size;
unsigned int nsamples;
unsigned int col;
struct parsed_options options;
init_parsed_options(&options);
@ -53,10 +58,23 @@ int main(int argc, char *argv[])
exit(1);
}
size = comedi_get_buffer_size(dev, options.subdevice);
fprintf(stderr,"buffer size is %d\n", size);
ret = comedi_get_buffer_size(dev, options.subdevice);
if(ret < 0){
comedi_perror("comedi_get_buffer_size");
exit(1);
}
bufsize = ret;
fprintf(stderr,"buffer size is %u\n", bufsize);
ret = comedi_get_subdevice_flags(dev, options.subdevice);
if(ret < 0){
comedi_perror("comedi_get_subdevice_flags");
}
subdev_flags = ret;
sample_size = (subdev_flags & SDF_LSAMPL)
? sizeof(lsampl_t) : sizeof(sampl_t);
fprintf(stderr,"sample size is %u\n", sample_size);
map = mmap(NULL,size,PROT_READ,MAP_SHARED, comedi_fileno(dev), 0);
map = mmap(NULL,bufsize,PROT_READ,MAP_SHARED, comedi_fileno(dev), 0);
fprintf(stderr, "map=%p\n", map);
if( map == MAP_FAILED ){
perror( "mmap" );
@ -89,24 +107,40 @@ int main(int argc, char *argv[])
front = 0;
back = 0;
bufpos = 0;
col = 0;
while(1){
front += comedi_get_buffer_contents(dev, options.subdevice);
if(options.verbose) fprintf(stderr, "front = %d, back = %d\n", front, back);
if(front < back) break;
ret = comedi_get_buffer_contents(dev, options.subdevice);
if(ret < 0){
comedi_perror("comedi_get_buffer_contents");
break;
}
front += ret;
nsamples = (front - back) / sample_size;
front = back + nsamples * sample_size;
if(options.verbose) fprintf(stderr, "front = %u, back = %u, samples = %u\n", front, back, nsamples);
if(front == back){
//comedi_poll(dev, options.subdevice);
usleep(10000);
continue;
}
for(i = 0; i < nsamples; i++){
unsigned int sample;
for(i = back; i < front; i += sizeof(sampl_t)){
static int col = 0;
printf("%d ",*(sampl_t *)(map + (i % size)));
if(sample_size == sizeof(sampl_t))
sample = *(sampl_t *)((char *)map + bufpos);
else
sample = *(lsampl_t *)((char *)map + bufpos);
printf("%u ", sample);
col++;
if(col == options.n_chan){
printf("\n");
col = 0;
}
bufpos += sample_size;
if(bufpos >= bufsize){
bufpos = 0;
}
}
ret = comedi_mark_buffer_read(dev, options.subdevice, front - back);