Doc updates

module_usb_audio/usb_buffer/get_adc_counts.c

@@ -0,0 +1,49 @@
+extern unsigned int g_curUsbSpeed;
+#define XUD_SPEED_HS 2
+
+/* Returns the max and min packet sizes to send back to host for a given sample frequency 
+ * See page 13 of USB Audio Device Class Definitions for Audio Data Formats Spec (v2.0) 
+ * 
+ * Audio samples per frame = INT(sampFreq/frametime); Variation allowed is + 1;
+ *
+ * For HS frame time = 8 * 1000
+ *
+ * so n = INT(SampFreq/8000) | INT (SampFreq/8000) + 1
+ *
+ * In the case where INT(SampFreq/8000) == SampFreq/8000) n may vary between
+ *
+ * INT(SamFreq/8000) - 1 | INT(SampFreq/8000) | INT (SampFreq/8000) + 1
+ *
+ * Note: Assumes HS (i.e. 8 frames per 1ms)
+ *
+ * Examples: 
+ * 44100:  min: 5  max: 6
+ * 48000:  min: 5  max: 7
+ * 96000:  min: 11 max: 13
+ * 88200:  min: 11 max: 12
+ * 176400: min: 22 max: 23
+ * 192000: min: 23 max: 25
+ *
+ */
+void GetADCCounts(unsigned samFreq, int *min, int *mid, int *max)
+{
+    unsigned frameTime;
+    int usb_speed;
+    usb_speed = g_curUsbSpeed;
+    if (usb_speed == XUD_SPEED_HS) 
+      frameTime = 8000;
+    else 
+      frameTime = 1000;
+
+    *min = samFreq / frameTime;
+    *max = *min + 1;
+
+    *mid = *min;
+
+    /* Check for INT(SampFreq/8000) == SampFreq/8000 */    
+    if((samFreq % frameTime) == 0)
+    {
+        *min -= 1;
+    }
+
+}