fix reporting to match time elapsed

Core/Src/main.c

@@ -34,11 +34,12 @@ typedef struct  {
 
 /* Private define ------------------------------------------------------------*/
 /* USER CODE BEGIN PD */
-#define SAMPLE_COUNT    (512)   // Sample count per half-transfer
-#define MIC_OFFSET_DB   (  0.f) // Linear offset
-#define MIC_SENSITIVITY (-26.f) // dBFS value expected at MIC_REF_DB
-#define MIC_REF_DB      ( 94.f) // dB where sensitivity is specified
-#define MIC_BITS        (18)
+#define SAMPLE_COUNT        (256)   // Sample count per half-transfer
+#define SAMPLES_PER_REPORT  (48000) // Report every second given our 48 kHz rate
+#define MIC_OFFSET_DB       (  0.f) // Linear offset
+#define MIC_SENSITIVITY     (-26.f) // dBFS value expected at MIC_REF_DB
+#define MIC_REF_DB          ( 94.f) // dB where sensitivity is specified
+#define MIC_BITS            (18)
 /* USER CODE END PD */
 
 /* Private macro -------------------------------------------------------------*/
@@ -58,7 +59,7 @@ UART_HandleTypeDef huart2;
 static const uint8_t I2S_Frame_Buffer[8] = {
   0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF
 };
-static uint8_t I2S_Receive_Buffer[SAMPLE_COUNT * sizeof(sample_t)];
+static uint8_t I2S_Receive_Buffer[SAMPLE_COUNT * 2 * sizeof(sample_t)];
 
 float ln10;
 float MIC_REF_AMPL;
@@ -547,16 +548,16 @@ void SPI_DMAHalfTransmitReceiveCplt(DMA_HandleTypeDef *hdma)
     float f = process(qfp_int2float(sample[i].value / 4));
     DB_Sum_Squares = qfp_fadd(DB_Sum_Squares, qfp_fmul(f, f));
   }
-  DB_Count += SAMPLE_COUNT / 8;
+  DB_Count += SAMPLE_COUNT * 2; // Pretend we sampled the entire I2S buffer
 
-  if (DB_Count > 48000 / 4) {
+  if (DB_Count > SAMPLES_PER_REPORT) {
     float rms = qfp_fsqrt(qfp_fdiv(DB_Sum_Squares, qfp_uint2float(DB_Count)));
     float db = qfp_fadd(MIC_OFFSET_DB + MIC_REF_DB, qfp_fmul(20.f,
       qfp_flog10(qfp_fdiv(rms, MIC_REF_AMPL))));
     DB_Sum_Squares = 0.f;
     DB_Count = 0;
 
-    printf("%d\r\n", qfp_float2int(db));
+    printf("%d dB\r\n", qfp_float2int(db));
   }
 }
 /* USER CODE END 4 */