Comment

Author: Cuda-Chen

virtio-snd.c

@@ -1,8 +1,8 @@
+#include <inttypes.h>
 #include <math.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <string.h>
-#include <inttypes.h>
 
 #define CNFA_IMPLEMENTATION
 #include "CNFA_sf.h"
@@ -580,7 +580,7 @@ static int virtio_snd_desc_handler(virtio_snd_state_t *vsnd,
                                    uint32_t *plen)
 {
     /* TODO: clarify the use of the third descriptor */
-    /* virtio-snd uses at most 3 virtqueue descriptors, where
+    /* virtio-snd command uses at most 3 virtqueue descriptors, where
      * the first descriptor contains:
      *   struct virtio_snd_hdr hdr (for request)
      * the second descriptors contains:
@@ -668,28 +668,28 @@ static int virtio_snd_tx_desc_handler(virtio_snd_state_t *vsnd,
                                       uint32_t desc_idx,
                                       uint32_t *plen)
 {
-    /* TODO: clarify the use of the third descriptor */
-    /* virtio-snd uses at most 3 virtqueue descriptors, where
-     * the first descriptor contains:
+    /* TODO: clarify the usage of last descriptor. */
+    /* virtio-snd TX uses arbitrary number of virtqueue descriptors.
+     * The first descritor descriptor contains:
      *   struct virtio_snd_hdr hdr (for request)
-     * the second descriptors contains:
-     *   struct virtio_snd_hdr hdr (for response)
-     * if needed, the third descriptors contains:
+     * Next, the payload consists of one or more descriptors
+     * representing PCM frames.
+     * Finally, the last descriptors contains:
      *   (response payload structure)
      */
     struct virtq_desc vq_desc[VSND_DESC_CNT];
 
     /* Collect the descriptors */
     int i = 0;
-    while(true) {
+    while (true) {
         /* The size of the `struct virtq_desc` is 4 words */
         const uint32_t *desc = &vsnd->ram[queue->QueueDesc + desc_idx * 4];
 
         /* Retrieve the fields of current descriptor */
-        if(i < VSND_DESC_CNT) {
-        vq_desc[i].addr = desc[0];
-        vq_desc[i].len = desc[2];
-        vq_desc[i].flags = desc[3];
+        if (i < VSND_DESC_CNT) {
+            vq_desc[i].addr = desc[0];
+            vq_desc[i].len = desc[2];
+            vq_desc[i].flags = desc[3];
         }
         desc_idx = desc[3] >> 16; /* vq_desc[desc_cnt].next */