From 558e594ba24b34cfd7374cf706b834479324c917 Mon Sep 17 00:00:00 2001
From: Taylor Holberton <taylorcholberton@gmail.com>
Date: Sun, 4 Dec 2016 13:42:28 -0800
Subject: Added pcm_link and pcm_unlink functions

The link function is necessary for time sychronization between multiple PCMs.
---
 include/tinyalsa/pcm.h |  4 ++++
 src/pcm.c              | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/tinyalsa/pcm.h b/include/tinyalsa/pcm.h
index 1d84eed..9157b9b 100644
--- a/include/tinyalsa/pcm.h
+++ b/include/tinyalsa/pcm.h
@@ -288,6 +288,10 @@ int pcm_mmap_begin(struct pcm *pcm, void **areas, unsigned int *offset, unsigned
 
 int pcm_mmap_commit(struct pcm *pcm, unsigned int offset, unsigned int frames);
 
+int pcm_link(struct pcm *pcm1, struct pcm *pcm2);
+
+int pcm_unlink(struct pcm *pcm);
+
 int pcm_prepare(struct pcm *pcm);
 
 int pcm_start(struct pcm *pcm);
diff --git a/src/pcm.c b/src/pcm.c
index f879fe7..b69316a 100644
--- a/src/pcm.c
+++ b/src/pcm.c
@@ -1053,6 +1053,38 @@ int pcm_is_ready(const struct pcm *pcm)
     return pcm->fd >= 0;
 }
 
+/** Links two PCMs.
+ * After this function is called, the two PCMs will prepare, start and stop in sync (at the same time).
+ * If an error occurs, the error message will be written to @p pcm1.
+ * @param pcm1 A PCM handle.
+ * @param pcm2 Another PCM handle.
+ * @return On success, zero; on failure, a negative number.
+ * @ingroup libtinyalsa-pcm
+ */
+int pcm_link(struct pcm *pcm1, struct pcm *pcm2)
+{
+    int err = ioctl(pcm1->fd, SNDRV_PCM_IOCTL_LINK, pcm2->fd);
+    if (err == -1) {
+        return oops(pcm1, errno, "cannot link PCM");
+    }
+    return 0;
+}
+
+/** Unlinks a PCM.
+ * @see @ref pcm_link
+ * @param pcm A PCM handle.
+ * @return On success, zero; on failure, a negative number.
+ * @ingroup libtinyalsa-pcm
+ */
+int pcm_unlink(struct pcm *pcm)
+{
+    int err = ioctl(pcm->fd, SNDRV_PCM_IOCTL_UNLINK);
+    if (err == -1) {
+        return oops(pcm, errno, "cannot unlink PCM");
+    }
+    return 0;
+}
+
 /** Prepares a PCM, if it has not been prepared already.
  * @param pcm A PCM handle.
  * @return On success, zero; on failure, a negative number.
-- 
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