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. */
buffer.cpp
- Committer:
- bw
- Date:
- 2014-03-27
- Revision:
- 0:bbf6cf0eab95
File content as of revision 0:bbf6cf0eab95:
/******************************************************************************* * 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; }