refactored I2S (base class)

io/teensy/I2SBaseDMA.h

@@ -0,0 +1,115 @@
+#pragma once
+
+
+#include <DMAChannel.h>
+
+/**
+ * base-class for I2S1 and I2S2 when using DMA
+ * the template parameter is only needed to allocate the static variables TWICE
+ * once for I2S1 and once for I2S2
+ */
+template <typename T> class I2SBase {
+
+
+protected:
+
+	/** the actual PCM data buffer, DMA throws an interrupt whenever a half of this buffer was transmitted */
+	static DMAMEM __attribute__((aligned(32))) int16_t buffer[I2S2_BUFFER_SAMPLES];
+
+	/** helper class to map one half of above buffer */
+	struct BufferHalf {
+
+		/** start of the data */
+		int16_t* mem;
+
+		/** number of samples that have been added during filling */
+		volatile uint16_t samplesUsed = 0;
+
+		/** ctor with the start of the memory for this half */
+		BufferHalf(int16_t* mem) : mem(mem) {}
+
+		/** number of samples that can be added befor the half is full */
+		uint16_t samplesFree() const {return I2S2_BUFFER_SAMPLES/2 - samplesUsed;}
+
+
+		//bool isFilled() const {return samplesFree() == 0;}
+
+		void dropCache() {arm_dcache_flush_delete(mem, I2S2_BUFFER_SAMPLES/2*sizeof(int16_t));}
+
+	};
+
+	struct State {
+
+		DMAChannel dma;
+
+		volatile uint8_t transmittingHalf = 0;
+
+		BufferHalf bufferHalf[2] = {
+		    BufferHalf(&buffer[0]),
+		    BufferHalf(&buffer[I2S2_BUFFER_SAMPLES/2]),
+		};
+
+		/** the current half was transmitted, switch to the next one */
+		void halfTransmitted() {
+			bufferHalf[transmittingHalf].samplesUsed = 0;
+			//memset(bufferHalf[transmittingHalf].mem, 0, I2S2_BUFFER_SAMPLES/2*sizeof(int16_t));
+			transmittingHalf = (transmittingHalf + 1) % 2;
+			bufferHalf[transmittingHalf].dropCache();
+		}
+
+		/** the BufferHalf we are currently filling when adding new data */
+		BufferHalf& fillingHalf() {
+			return bufferHalf[(transmittingHalf+1)%2];
+		}
+
+	};
+
+	static State state;
+
+	/** ISR, called whenever one half of the buffer was transmitted */
+	FASTRUN static void isrDMA() {
+
+		state.dma.clearInterrupt();
+		state.halfTransmitted();
+
+	}
+
+public:
+
+	/** zero-out the audio buffer */
+	static void clearBuffer() {
+		memset(buffer, 0, sizeof(buffer));
+		state.bufferHalf[0].samplesUsed = 0;
+		state.bufferHalf[1].samplesUsed = 0;
+	}
+
+	/** block until the given number of samples were added to the internal buffer */
+	static void addBlocking(const int16_t* pcm, uint16_t numSamples) {
+		while(numSamples) {
+			const uint32_t samplesAdded = addNonBlocking(pcm, numSamples);
+			numSamples -= samplesAdded;
+			pcm += samplesAdded;
+		}
+	}
+
+	/** add the given number of samples to the internal buffer, returns the number of actually added samples, dependent on how much space there was */
+	static uint16_t addNonBlocking(const int16_t* pcm, uint16_t numSamples) {
+
+		// determine the half of the buffer we are currently writing to
+		BufferHalf& bh = state.fillingHalf();
+
+		// determine how many samples to add
+		const uint16_t addable = min(numSamples, bh.samplesFree());
+
+		// actually copy the data
+		uint8_t* dst = (uint8_t*) (&bh.mem[bh.samplesUsed]);
+		uint16_t numBytes = addable * sizeof(int16_t);
+		memcpy(dst, pcm, numBytes);
+
+		// adjust the buffer half's information
+		bh.samplesUsed += addable;
+		return addable;
+
+	}
+
+};