player.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>

#include "fm_decoder.h"
#include "sdr.h"

struct {
	int			handle;
	uint32_t		freq;
} dongle;

int main( int argc, char **argv ) {
	uint8_t *input;
	uint16_t *output;
	ssize_t bytes;

	// Allows using aplay without tons of options
	uint32_t wav_header[] = {
		0x46464952	// "RIFF"
	,	~0		// near-infinite total size to allow streaming
	,	0x45564157	// "WAVE"
	,	0x20746d66	// "fmt "
	,	16		// size of the header
	,	0x10001		// 1 channel (mono) + PCM format
	,	32000		// Sample rate
	,	64000		// Bytes per second, essentially
	,	0x00100002	// 2-block sample alignment + 16 bits per sample
	,	0x61746164	// "data"
	,	~0		// near-infinite size to allow streaming
	};

	if ( argc < 2 ) {
		fprintf( stderr, "Usage:\n\t%s <frequency> | aplay\n", argv[0] );
		return 1;
	}

	if ( isatty( fileno( stdout ) ) ) {
		fprintf( stderr,
			"This tool outputs a 16-bit 32KHz PCM .WAV file to standard out,\n"
			"intended for piping to aplay, play, or other tool of your choice.\n"
			"\n"
			"To avoid spamming up your terminal and beeping like mad, exiting.\n" );
	}

	// This construct limits any input number to valid NA FM frequencies only
	dongle.freq = ( uint32_t )( atof( argv[1] ) * 5 );
	dongle.freq = ( dongle.freq + 160 ) % 100;

	dongle.handle = sdr_init();
	if ( dongle.handle == -1 ) {
		fprintf( stderr, "Failed to locate/initialize Software Defined Radio.\n" );
		return 1;
	}

	// The construct reverses the initial compaction of inputs, to avoid needing
	// any real error handling for invalid frequency requests: You just get some
	// valid frequency that is modulus nearby automagically.
	if ( sdr_tune( dongle.handle, ( ( dongle.freq + 440 ) * 200000 ) + 100000 ) != 0 ) {
		fprintf( stderr, "Failed to set radio frequency.\n" );
		close( dongle.handle );
		return 1;
	}

	input = malloc( 64 * 32 * 1024 );
	if ( input == NULL ) {
		fprintf( stderr, "Failed to allocate input buffer!\n" );
	}

	output = malloc(     32 * 1024 );
	if ( output == NULL ) {
		fprintf( stderr, "Failed to allocate output buffer!\n" );
	}

	// Need to reset the 'carryover' IQ values to avoid a first-sample noise blart
	fm_decoder_reset();

	// Pitch out the WAV header so we can be piped into aplay/play/mplayer/etc
	fwrite( wav_header, sizeof( wav_header ), 1, stdout );

	for ( ; ; ) {
		bytes = read( dongle.handle, input, 2048 * 1024 );
		if ( bytes == -1 ) {
			break;
		}

		// The decoder routine requires 128 bytes
		// for each 2-byte sample generated.
		//
		// In practice this is never an issue as the
		// read gets full buffers or at least power-
		// of-2 worth of data at once.
		bytes &= ~127;

		// Make it so, Number 2!
		fm_decoder_process( input, bytes, output );

		// ...and play me those sweet, dulcet tones.
		fwrite( output, bytes / 64, 1, stdout );
	}

	close( dongle.handle );
}