Implement volume limiter feature

Add a "volume limit" parameter to the configuration file. The maximum
value of volume setting in sound menu will be limited to the same as
volume limit. Also each time when setvol() is excuted, Rockbox will
check if the global_settings.volume value larger than
global_settings.volume_limit. If larger, take the value of volume_limit
instead. The volume_limit argument shares the same maximum and minimum values
with volume argument, while taking the maximum volume as its default value.

Change-Id: I8ca9bc6ea6e617b48fc346aae5f2a0a1d259ae36
Reviewed-on: http://gerrit.rockbox.org/697
Reviewed-by: Jonathan Gordon <rockbox@jdgordon.info>

1 files changed, 1 insertions, 0 deletions

diff --git a/apps/settings.h b/apps/settings.h
index 087ff0cb45..62ae038385 100644
--- a/apps/settings.h
+++ b/apps/settings.h
@@ -828,6 +828,7 @@ struct user_settings
 #ifdef HAVE_PLAY_FREQ
     int play_frequency; /* core audio output frequency selection */
 #endif
+    int volume_limit; /* maximum volume limit */
 };
 
 /** global variables **/