From 65063d785ea505d8d7903c5a0242b026a31efccc Mon Sep 17 00:00:00 2001
From: Ian Abbott <abbotti@mev.co.uk>
Date: Mon, 23 Nov 2015 16:04:11 +0000
Subject: [PATCH] demo/mmap: support integer wraparound and large sample size

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'.
---
 demo/mmap.c | 58 ++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 46 insertions(+), 12 deletions(-)

diff --git a/demo/mmap.c b/demo/mmap.c
index 55bf58d..46042c5 100644
--- a/demo/mmap.c
+++ b/demo/mmap.c
@@ -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);