bryan wade
Streams USB audio with sound effects applied. Sound effect selected by joystick and intensity altered by tilting the mbed. Output to the mbed-application-board phono jack.
Dependencies: C12832_lcd MMA7660 USBDevice mbed
/* Uses the mbed LPC1768 and mbed-application-board to create a USB audio device * that streams audio from a host computer to headphones or powered speakers. * A couple different sound effects can be applied to the stream in real-time, * and tilting the mbed alters intensity of the effect. * * ECHO * The joystick selects ) | * one of three effect ) STRAIGHT - o - STRAIGHT * modes. ) | * REVERB * * * * \\ || * Tilting the mbed ) ====== \\ || * determines intensity ) \\ || * of the effect. ) * 0% 50% 100% * * The LCD display shows the current effect mode, intesity and buffer level. */
Diff: buffer.cpp
- Revision:
- 0:bbf6cf0eab95
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/buffer.cpp Thu Mar 27 21:27:04 2014 +0000
@@ -0,0 +1,89 @@
+/*******************************************************************************
+ * Implements FIFO buffer for glitch-free audio playback.
+ * Bryan Wade
+ * 27 MAR 2014
+ ******************************************************************************/
+#include "buffer.h"
+#include "string.h"
+
+struct buffer_t { // Implementation of opaque type.
+ int16_t *base;
+ int16_t *head;
+ int16_t *tail;
+ size_t len;
+};
+
+/*
+ * Create a buffer object given a ptr and size of available RAM.
+ * @return Ptr to the new buffer.
+ */
+buffer_t *Buffer_Create(void *ram, size_t size)
+{
+ buffer_t *buffer = (buffer_t *)malloc(sizeof(buffer_t));
+ if (buffer) {
+ buffer->base = (int16_t *)ram;
+ buffer->len = size / sizeof(int16_t);
+ memset(ram, 0, size);
+ buffer->head = buffer->tail = buffer->base;
+ }
+ return buffer;
+}
+
+/*
+ * Read a single sample from the buffer.
+ * @return True if successful (no underflow).
+ */
+bool Buffer_Read(buffer_t *buffer, int16_t *pDataOut)
+{
+ if (buffer->head == buffer->tail)
+ return false;
+
+ *pDataOut = *buffer->tail;
+
+ if (++buffer->tail >= buffer->base + buffer->len) {
+ buffer->tail = buffer->base;
+ }
+
+ return true;
+}
+
+/*
+ * Write a single sample to the buffer.
+ */
+void Buffer_Write(buffer_t *buffer, int16_t dataIn)
+{
+ if (Buffer_GetLevel(buffer) >= buffer->len - 1)
+ return;
+
+ *buffer->head = dataIn;
+
+ if (++buffer->head >= buffer->base + buffer->len)
+ buffer->head = buffer->base;
+}
+
+/*
+ * Write a block of data to the buffer.
+ */
+void Buffer_WriteBlock(buffer_t *buffer, const int16_t *pDataIn, uint32_t length)
+{
+ int i;
+ for (i = 0; i < length; i++) {
+ Buffer_Write(buffer, pDataIn[i]);
+ }
+}
+
+/*
+ * Get buffer level
+ */
+int32_t Buffer_GetLevel(buffer_t *buffer)
+{
+ __disable_irq(); /* Begin critical section */
+
+ int32_t level = (buffer->head >= buffer->tail) ?
+ buffer->head - buffer->tail :
+ buffer->len + buffer->head - buffer->tail;
+
+ __enable_irq(); /* End critical section */
+
+ return level;
+}
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