--- a/data-provider.h	Wed Jan 22 14:45:23 2014 +0100
+++ b/data-provider.h	Wed Jan 22 14:45:24 2014 +0100
@@ -12,23 +12,21 @@
 /* callback receiving messages in the main thread */
 void CVICALLBACK MessageCB (void *callbackData);
 
+/* number of data channels */
+#define NCHAN 4
+
 /* data acquisition event */
 struct event {
 	struct timeval time;
-	double data[4];
+	double data[NCHAN];
 };
 
-/* message buffer */
-#define DATA_PROVIDER_MSGLEN 256
-#define DATA_PROVIDER_MSGNUM 16
-static char messages[DATA_PROVIDER_MSGLEN][DATA_PROVIDER_MSGNUM];
-static unsigned int messageid = 0;
+/* send messages to the main thread */
+void SendMessage(int threadId, const char *frmt, ...);
 
-#define SendMessage(threadId, ...)                                     \
-	do {                                                               \
-		char *message = messages[messageid++ % DATA_PROVIDER_MSGNUM];  \
-		snprintf(message, DATA_PROVIDER_MSGLEN - 1, ##__VA_ARGS__);    \
-		PostDeferredCallToThread(MessageCB, message, threadId);        \
-	} while (0)
+/* data providers */
+int CVICALLBACK FakeDataProvider (void *functionData);
+int CVICALLBACK FileDataProvider (void *functionData);
+int CVICALLBACK KKDataProvider (void *functionData);
 
 #endif