/**
 * Functions which control the PC speaker.  You must execute this code as root
 * otherwise the beep(..) function will crash with error message 'Segmentation
 * fault'.
 *
 * Tested under Linux 2.4 on Intel architecture only.
 *
 * Author: Adam Buckley, adambuckley@gmx.net
 * Version: $Id: beep.c,v 1.2 2002/05/23 12:13:55 adam Exp $
 */


/**
 * This source code is copyright (c) 2002 Adam Buckley, <adambuckley@gmx.net>.
 *
 * This source code is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU General Public License as published by the Free 
 * Software Foundation; either version 2 of the License, or (at your option) 
 * any later version.
 *
 * This source code is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for 
 * more details.
 *
 * The GNU General Public License can be found at
 * http://www.gnu.org/licenses/gpl.html
 */


#ifndef ADAMLIB_BEEP_C
#define ADAMLIB_BEEP_C

#include <sys/io.h>



/**
 * Makes a PC beep of frequency 'frequency' and of length 'length' in
 * microseconds.
 *
 * This function will block for 'length' microseconds.
 *
 * Note, because this function uses low level port input and output, the user
 * must be root, otherwise a Segmentation Fault will occur.
 *
 * Note also, from the man pages of 'outb':
 *
 *    You compile with -O or -O2 or similar. The functions are defined as
 *    inline macros, and will not be substituted in without optimization
 *    enabled, causing unresolved references at link time.
 */
void beep(unsigned int frequency, unsigned int length)
{
	unsigned int count = 1193180 / frequency;
	
	// Grant this user process permissions to access ports
	// The user must be 'root' in order for these lines to succeed
	ioperm(0x61, 0x20, 1);
	ioperm(0x42, 0x02, 1);
	
	// Switch on the speaker
	outb_p(inb_p(0x61)|3, 0x61);
	
	// Set command for counter 2, 2 byte write
	outb_p(0xB6, 0x43);
	
	// Select desired Hz
	outb_p(count & 0xff, 0x42);
	outb((count >> 8) & 0xff, 0x42);
	
	// Block for 'length' microseconds
	usleep(length);
	
	// Switch off the speaker
	outb(inb_p(0x61)&0xFC, 0x61);
}



int lookUpTable[128];
char haveMadeLookupTable = 0;

/**
 * Builds the MIDI note number >> Hz table, ie. populates 'lookUpTable'.
 *
 * This function is called automatically by midiToHz(..)
 */
void makeLookupTable()
{
	int i;
	
	// Frequency of MIDI note 0 in Hz
	float frequency = 8.175799;
	
	// Ratio: 2 to the power 1/12
	float ratio = 1.0594631;
	
	for(i=0; i<128; i++)
	{
		lookUpTable[i] = (int) frequency;  // Put value into table
		frequency = frequency * ratio; // Find next note in hertz
	}
}



/**
 * Returns the frequency in Hz of the specified MIDI note number.
 *
 * If noteNumber is smaller than 0 or greater than 127 then this function
 * returns the frequency of MIDI note 60.
 */
int midiToHz(unsigned char noteNumber)
{
	if(haveMadeLookupTable==0)
	{
		makeLookupTable();
		haveMadeLookupTable = 1;
	}
	
	// Unnecessary, because an unsigned char is always > 0
	//if(noteNumber<0) noteNumber = 60;

	if(noteNumber>127) noteNumber = 60;
	
	return lookUpTable[noteNumber];
}



/**
 * Makes a PC beep of MIDI note number 'noteNumber' and of length 'length' in
 * microseconds.
 *
 * If 'noteNumber' is not between 0 and 127, then this function will default
 * to MIDI note 60.
 *
 * This function will block for 'length' microseconds.
 *
 * Note, because this function uses low level port input and output, the user
 * must be root, otherwise a Segmentation Fault will occur.
 */
void beepNote(unsigned char noteNumber, unsigned int length)
{
	beep(midiToHz(noteNumber), length);
}



/**
 * Silences the PC speaker
 */
void beepOff()
{
	// Switch off the speaker
	outb(inb_p(0x61)&0xFC, 0x61);
}

#endif