Interim stash: Implementing circular buffer

Author: nseidle

libraries/PDM/src/PDM.cpp

@@ -24,9 +24,6 @@ SOFTWARE.
 AP3_PDM *ap3_pdm_handle = 0;
 am_hal_pdm_transfer_t sTransfer;
 
-#define internalPDMDataBufferSize 4096 //Default is array of 4096 * 32bit
-uint32_t internalPDMDataBuffer[internalPDMDataBufferSize];
-
 bool AP3_PDM::begin(ap3_gpio_pin_t pinPDMData, ap3_gpio_pin_t pinPDMClock)
 {
     _PDMhandle = NULL;
@@ -43,7 +40,16 @@ bool AP3_PDM::begin(ap3_gpio_pin_t pinPDMData, ap3_gpio_pin_t pinPDMClock)
 
 bool AP3_PDM::available(void)
 {
-    return (_PDMdataReady);
+    if (_head != _tail)
+        return (true);
+    return (false);
+}
+
+bool AP3_PDM::isOverrun(void)
+{
+    if (_overrun == true)
+        return (true);
+    return (false);
 }
 
 ap3_err_t AP3_PDM::_begin(void)
@@ -274,45 +280,45 @@ ap3_err_t ap3_pdm_pad_funcsel(ap3_pdm_pad_type_e type, ap3_gpio_pad_t pad, uint8
 //*****************************************************************************
 uint32_t AP3_PDM::getData(uint32_t *externalBuffer, uint32_t bufferSize)
 {
-    if (_PDMdataReady)
-    {
-        if (bufferSize > internalPDMDataBufferSize)
-            bufferSize = internalPDMDataBufferSize;
-
-        noInterrupts();
+    if (bufferSize > circularBufferSize)
+        bufferSize = circularBufferSize;
 
-        //Move data from internal buffer to external caller
-        for (int x = 0; x < bufferSize; x++)
-            externalBuffer[x] = internalPDMDataBuffer[x];
+    noInterrupts();
 
-        interrupts();
-    }
-    _PDMdataReady = false;
+    //Move data from internal buffer to external caller
+    for (int x = 0; x < bufferSize; x++)
+        externalBuffer[x] = _pdmCircularBuffer[x];
 
-    //Start next conversion
-    am_hal_pdm_dma_start(_PDMhandle, &sTransfer);
+    interrupts();
+}
 }
 
 inline void AP3_PDM::pdm_isr(void)
 {
     uint32_t ui32Status;
 
-    //
     // Read the interrupt status.
-    //
     am_hal_pdm_interrupt_status_get(_PDMhandle, &ui32Status, true);
     am_hal_pdm_interrupt_clear(_PDMhandle, ui32Status);
 
     if (ui32Status & AM_HAL_PDM_INT_DCMP)
     {
-        if (_PDMdataReady == true)
+        //Move current DMA to circular buffer
+        for (int x = 0; x < pdmDataBufferSize; x++)
+        {
+            _pdmCircularBuffer[head++] = _pdmDataBuffer[x];
+            if (_head++ == circularBufferSize)
+                _head = 0;
+        }
+
+        if (_head == _tail)
         {
-            //If flag has not previously been cleared, we're overrun
-            //Serial.println("Buffer overrun!");
+            Serial.println("Buffer overrun!");
+            _overrun = true;
         }
 
-        //New data has been loaded into internalPDMDataBuffer
-        _PDMdataReady = true;
+        //Start next conversion
+        am_hal_pdm_dma_start(_PDMhandle, &sTransfer);
     }
 }
 

libraries/PDM/src/PDM.h

@@ -96,7 +96,8 @@ class AP3_PDM
 {
 public:
     bool begin(ap3_gpio_pin_t pinPDMData = MIC_DATA, ap3_gpio_pin_t pinPDMClock = MIC_CLOCK);
-    bool available(void); //Goes true once an interrupt has occured
+    bool available(void); //Goes true if circular buffer is not empty
+    bool isOverrun(void); //Goes true if head crosses tail
 
     bool setClockSpeed(am_hal_pdm_clkspd_e clockSpeed);
     am_hal_pdm_clkspd_e getClockSpeed();
@@ -126,7 +127,17 @@ class AP3_PDM
 
     ap3_err_t _begin(void);
 
-    volatile bool _PDMdataReady = false;
+    //volatile bool _PDMdataReady = false;
+
+    volatile bool _head = 0;
+    volatile bool _tail = 0;
+    volatile bool _overrun = false;
+
+    const int pdmDataBufferSize = 512;                   //Default is array of 4096 * 32bit
+    volatile uint32_t _pdmDataBuffer[pdmDataBufferSize]; //This has been filled previous to ISR being called
+
+    const int circularBufferSize = 4096;
+    volatile uint32_t _pdmCircularBuffer[circularBufferSize]; //This is filled by ISR and read by getData
 };
 
 #endif //_PDM_H_