reduce process cycles; fix sample bit-order

2 files changed, 42 insertions, 33 deletions

diff --git a/Core/Src/main.c b/Core/Src/main.c
index 67e6ab8..7c41e3f 100644
--- a/Core/Src/main.c
+++ b/Core/Src/main.c
@@ -27,19 +27,17 @@
 

 /* Private typedef -----------------------------------------------------------*/

 /* USER CODE BEGIN PTD */

-typedef struct  {

-    int32_t value : 18;

-} sample_t;

+typedef uint32_t sample_t;

 /* USER CODE END PTD */

 

 /* Private define ------------------------------------------------------------*/

 /* USER CODE BEGIN PD */

-#define SAMPLE_COUNT        (256)   // Sample count per half-transfer

+#define SAMPLE_COUNT        (256)   // (Stereo!) 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)

+#define MIC_BITS            (18u)

 /* USER CODE END PD */

 

 /* Private macro -------------------------------------------------------------*/

@@ -104,7 +102,7 @@ int main(void)
 

   /* USER CODE BEGIN 1 */

   ln10 = qfp_fln(10.f);

-  MIC_REF_AMPL = qfp_fmul(qfp_int2float((1 << (MIC_BITS - 1)) - 1),

+  MIC_REF_AMPL = qfp_fmul(qfp_int2float((1u << (MIC_BITS - 1)) - 1),

     qfp_fpow(10.f, MIC_SENSITIVITY / 20.f));

   /* USER CODE END 1 */

 

@@ -443,53 +441,64 @@ error :
   return errorcode;

 }

 

-void SPI_DMATransmitReceiveCplt(DMA_HandleTypeDef *hdma)

-{

-  SPI_HandleTypeDef *hspi = (SPI_HandleTypeDef *)hdma->Parent;

-  (void)hspi;

-}

-

-static float process(float in_div4)

+static inline float process(float in_div4)

 {

-    static float z1 = 0, z2 = 0, z3 = 0, z5 = 0;

+    static float z[4] = {0.f, 0.f, 0.f, 0.f};

 

-    float out1 = qfp_fadd(in_div4, z1);

-    z1 = qfp_fadd(qfp_fmul(1.062f, out1), z2);

-    z2 = qfp_fsub(qfp_fmul(-0.14f, out1), in_div4);

+    float out1 = qfp_fadd(in_div4, z[0]);

+    z[0] = qfp_fadd(qfp_fmul(out1, 1.062f), z[1]);

+    z[1] = qfp_fsub(qfp_fmul(out1, -0.14f), in_div4);

 

-    float out2 = qfp_fadd(out1, z3);

-    z3 = out1;

+    float out2 = qfp_fadd(out1, z[2]);

+    z[2] = out1;

 

-    float out3 = qfp_fadd(out2, z5);

-    z5 = qfp_fsub(qfp_fmul(0.985f, out3), out2);

+    float out3 = qfp_fadd(out2, z[3]);

+    z[3] = qfp_fsub(qfp_fmul(out3, 0.985f), out2);

 

     return out3;

 }

 

-void SPI_DMAHalfTransmitReceiveCplt(DMA_HandleTypeDef *hdma)

+static void processSampleBlock(sample_t *sample)

 {

   HAL_GPIO_WritePin(IDLE_GPIO_Port, IDLE_Pin, GPIO_PIN_RESET);

 

-  SPI_HandleTypeDef *hspi = (SPI_HandleTypeDef *)hdma->Parent;

-  (void)hspi;

+  // SAMPLE_COUNT is number of samples in this block

+  // Divide by 2 for left channel only

+  // Divide by 8 for stride to reduce compute time

+#define STRIDE (2 * 8)

+

+  for (int i = 0; i < SAMPLE_COUNT; i += STRIDE) {

+    // 18-bit sample comes in as big-endian with right padding.

+    // 1. Convert to little-endian:

+    int samp;

+    asm("rev %0, %1" : "=r" (samp) : "r" (sample[i]));

+    // 2. Arithmetic shift right to remove padding, +2 to make "in_div4"

+    float f = process(qfp_int2float(samp >> (32 - MIC_BITS + 2)));

 

-  sample_t *sample = (sample_t *)I2S_Receive_Buffer;

-  for (int i = 0; i < SAMPLE_COUNT / 8; i++) {

-    float f = process(qfp_int2float(sample[i].value / 4));

-    DB_Sum_Squares = qfp_fadd(DB_Sum_Squares, qfp_fmul(f, f));

+    DB_Sum_Squares = qfp_fadd(qfp_fmul(f, f), DB_Sum_Squares);

   }

-  DB_Count += SAMPLE_COUNT * 2; // Pretend we sampled the entire I2S buffer

+  DB_Count += SAMPLE_COUNT / STRIDE;

 

-  if (DB_Count > SAMPLES_PER_REPORT) {

+  if (DB_Count >= SAMPLES_PER_REPORT / STRIDE * 2) {

     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))));

+    float db = qfp_fadd(qfp_fmul(qfp_flog10(qfp_fdiv(rms, MIC_REF_AMPL)), 20.f),

+        MIC_OFFSET_DB + MIC_REF_DB);

     DB_Sum_Squares = 0.f;

     DB_Count = 0;

 

     printf("%d dB\r\n", qfp_float2int(db));

   }

 }

+

+void SPI_DMATransmitReceiveCplt(DMA_HandleTypeDef *hdma)

+{

+  processSampleBlock((sample_t *)I2S_Receive_Buffer + SAMPLE_COUNT);

+}

+

+void SPI_DMAHalfTransmitReceiveCplt(DMA_HandleTypeDef *hdma)

+{

+  processSampleBlock((sample_t *)I2S_Receive_Buffer);

+}

 /* USER CODE END 4 */

 

 /**

diff --git a/Makefile b/Makefile
index ab0211a..b26e4da 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 ##########################################################################################################################

-# File automatically-generated by tool: [projectgenerator] version: [4.5.0-RC5] date: [Thu Jan 30 17:24:56 EST 2025] 

+# File automatically-generated by tool: [projectgenerator] version: [4.5.0-RC5] date: [Fri Jan 31 17:56:51 EST 2025] 

 ##########################################################################################################################

 

 # ------------------------------------------------