Implement universal in-PCM-driver software volume control.

Implements double-buffered volume, balance and prescaling control in
the main PCM driver when HAVE_SW_VOLUME_CONTROL is defined ensuring
that all PCM is volume controlled and level changes are low in latency.

Supports -73 to +6 dB using a 15-bit factor so that no large-integer
math is needed.

Low-level hardware drivers do not have to implement it themselves but
parameters can be changed (currently defined in pcm-internal.h) to work
best with a particular SoC or to provide different volume ranges.

Volume and prescale calls should be made in the codec driver. It should
appear as a normal hardware interface. PCM volume calls expect .1 dB
units.

Change-Id: Idf6316a64ef4fb8abcede10707e1e6c6d01d57db
Reviewed-on: http://gerrit.rockbox.org/423
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Tested-by: Michael Sevakis <jethead71@rockbox.org>

1 files changed, 40 insertions, 0 deletions

diff --git a/firmware/export/pcm_sw_volume.h b/firmware/export/pcm_sw_volume.h
new file mode 100644
index 0000000000..b86e78f500
--- /dev/null
+++ b/firmware/export/pcm_sw_volume.h
@@ -0,0 +1,40 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2013 by Michael Sevakis
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#ifndef PCM_SW_VOLUME_H
+#define PCM_SW_VOLUME_H
+
+#ifdef HAVE_SW_VOLUME_CONTROL
+
+#include <audiohw.h>
+
+#define PCM_MUTE_LEVEL INT_MIN
+
+#ifdef AUDIOHW_HAVE_PRESCALER
+/* Set the prescaler value for all PCM playback */
+void pcm_set_prescaler(int prescale);
+#endif /* AUDIOHW_HAVE_PRESCALER */
+
+/* Set the per-channel volume cut/gain for all PCM playback */
+void pcm_set_master_volume(int vol_l, int vol_r);
+
+#endif /* HAVE_SW_VOLUME_CONTROL */
+
+#endif /* PCM_SW_VOLUME_H */