hal: a stream of depth N holds N samples

src/hal/components/histobinstream.comp

@@ -122,9 +122,8 @@ EXTRA_SETUP() {
 
     int err;
     // One complete set is MAXBINNUMBER+2 records: the negative tail, every
-    // bin and the positive tail. The ring buffer's usable capacity is depth-1
-    // (one slot reserved), so add 1 to fit it.
-    if (0 != (err = hal_stream_create(&fifo, comp_id, keys[extra_arg], MAXBINNUMBER + 2 + 1, "u")))
+    // bin and the positive tail.
+    if (0 != (err = hal_stream_create(&fifo, comp_id, keys[extra_arg], MAXBINNUMBER + 2, "u")))
         return err;
     // The other side should run hal_stream_attach(&fifo, comp_id, key, "u")
     return 0;

src/hal/components/latencybinstream.comp

@@ -101,9 +101,8 @@ EXTRA_SETUP() {
 	if (extra_arg < 0 || extra_arg >= MAX_INST || !keys[extra_arg])
 		return -EINVAL;
 	int err;
-	// One complete set is 2*MAXBINNUMBER+1+2 records. The ring buffer's
-	// usable capacity is depth-1 (one slot reserved), so add 1 to fit it.
-	if (0 != (err = hal_stream_create(&fifo, comp_id, keys[extra_arg], 2*MAXBINNUMBER + 1 + 2 + 1, "u")))
+	// One complete set is 2*MAXBINNUMBER+1+2 records.
+	if (0 != (err = hal_stream_create(&fifo, comp_id, keys[extra_arg], 2*MAXBINNUMBER + 1 + 2, "u")))
 		return err;
 	// The other side should run hal_stream_attach(&fifo, comp_id, LBSKEY, "u")
 	return 0;

src/hal/hal_lib.c

@@ -4358,7 +4358,7 @@ typedef struct __hal_stream_shm_t {
     atomic_uint in;
     atomic_uint out;
     unsigned this_sample;
-    unsigned depth;
+    unsigned depth;             // capacity in samples; the ring has depth+1 slots
     int num_pins;
     atomic_uint num_overruns;
     atomic_uint num_underruns;
@@ -4427,7 +4427,7 @@ int hal_stream_create(hal_stream_t *stream, int comp, int key, unsigned depth, c
     if(!result) return -EINVAL;
     int pin_count = result;
 
-    size_t size = sizeof(hal_stream_shm_t) + sizeof(hal_stream_data_u) * depth * (1+pin_count);
+    size_t size = sizeof(hal_stream_shm_t) + sizeof(hal_stream_data_u) * (depth + 1) * (1+pin_count);
     result = rtapi_shmem_new(key, comp, size);
     if(result < 0) return result;
     stream->shmem_id = result;
@@ -4455,8 +4455,9 @@ void hal_stream_destroy(hal_stream_t *stream)
 
 static inline unsigned hal_stream_advance(hal_stream_t *stream, unsigned n)
 {
+    // one slot more than depth, so a full ring is not mistaken for empty
     n += 1;
-    if(n >= stream->fifo->depth) return 0;
+    if(n > stream->fifo->depth) return 0;
     return n;
 }
 
@@ -4546,7 +4547,7 @@ int hal_stream_depth(hal_stream_t *stream)
     unsigned out = hal_stream_atomic_load_out(stream);
     unsigned in  = hal_stream_atomic_load_in(stream);
     if(out > in)
-        return stream->fifo->depth + in - out;
+        return stream->fifo->depth + 1 + in - out;
     return in - out;
 }
 
@@ -4633,7 +4634,7 @@ int hal_stream_attach(hal_stream_t *stream, int comp_id, int key, const char *ty
     /* now use data in fifo structure to calculate proper shmem size */
     unsigned depth = fifo->depth;
     int pin_count = fifo->num_pins;
-    size_t size = sizeof(hal_stream_shm_t) + sizeof(hal_stream_data_u) * depth * (1+pin_count);
+    size_t size = sizeof(hal_stream_shm_t) + sizeof(hal_stream_data_u) * (depth + 1) * (1+pin_count);
     /* close shmem, re-open with proper size */
     rtapi_shmem_delete(shmem_id, comp_id);
     shmem_id = result = rtapi_shmem_new(key, comp_id, size);

tests/halmodule/stream/stream_reader.py

@@ -3,7 +3,7 @@
 import time
 c = hal.component("stream_reader")
 reader = hal.stream(c, hal.streamer_base, "bfsu")
-for i in range(9):
+for i in range(10):
     assert reader.readable
     assert reader.read() == ((i % 2, i, i, i))
     assert reader.num_underruns == 0

tests/halmodule/stream/stream_writer.py

@@ -4,7 +4,7 @@
 c = hal.component("stream_writer")
 writer = hal.stream(c, hal.streamer_base, 10, "bfsu")
 
-for i in range(9):
+for i in range(10):
     assert writer.writable
     writer.write((i % 2, i, i, i))
 assert not writer.writable