New version

audio/oss.cpp

@@ -3,12 +3,7 @@
 #include <sys/ioctl.h>
 #include <sys/soundcard.h>
 
-//OSS4 soundcard.h includes below SNDCTL defines, but OSS3 does not
+//OSSv4 features: define fallbacks for OSSv3 (where these ioctls are ignored)
-//However, OSS4 soundcard.h does not reside in <sys/>
-//Therefore, attempt to manually define SNDCTL values if using OSS3 header
-//Note that if the defines below fail to work on any specific platform, one can point soundcard.h
-//above to the correct location for OSS4 (usually /usr/lib/oss/include/sys/soundcard.h)
-//Failing that, one can disable OSS4 ioctl calls inside init() and remove the below defines
 
 #ifndef SNDCTL_DSP_COOKEDMODE
   #define SNDCTL_DSP_COOKEDMODE _IOW('P', 30, int)
@@ -31,12 +26,14 @@ struct AudioOSS : Audio {
     string device = "/dev/dsp";
     bool synchronize = true;
     uint frequency = 48000;
+    uint latency = 60;
   } settings;
 
   auto cap(const string& name) -> bool {
     if(name == Audio::Device) return true;
     if(name == Audio::Synchronize) return true;
     if(name == Audio::Frequency) return true;
+    if(name == Audio::Latency) return true;
     return false;
   }
 
@@ -44,6 +41,7 @@ struct AudioOSS : Audio {
     if(name == Audio::Device) return settings.device;
     if(name == Audio::Synchronize) return settings.synchronize;
     if(name == Audio::Frequency) return settings.frequency;
+    if(name == Audio::Latency) return settings.latency;
     return {};
   }
 
@@ -66,6 +64,12 @@ struct AudioOSS : Audio {
       return true;
     }
 
+    if(name == Audio::Latency && value.is<uint>()) {
+      settings.latency = value.get<uint>();
+      if(device.fd >= 0) init();
+      return true;
+    }
+
     return false;
   }
 
@@ -81,13 +85,11 @@ struct AudioOSS : Audio {
     device.fd = open(settings.device, O_WRONLY, O_NONBLOCK);
     if(device.fd < 0) return false;
 
-    #if 1 //SOUND_VERSION >= 0x040000
+    int cooked = 1;
-    //attempt to enable OSS4-specific features regardless of version
-    //OSS3 ioctl calls will silently fail, but sound will still work
-    int cooked = 1, policy = 4; //policy should be 0 - 10, lower = less latency, more CPU usage
     ioctl(device.fd, SNDCTL_DSP_COOKEDMODE, &cooked);
+    //policy: 0 = minimum latency (higher CPU usage); 10 = maximum latency (lower CPU usage)
+    int policy = min(10, settings.latency / 20);  //note: latency measurement isn't exact
     ioctl(device.fd, SNDCTL_DSP_POLICY, &policy);
-    #endif
     int frequency = settings.frequency;
     ioctl(device.fd, SNDCTL_DSP_CHANNELS, &device.channels);
     ioctl(device.fd, SNDCTL_DSP_SETFMT, &device.format);