#include  <pic.h>

__CONFIG(WDTDIS & XT & UNPROTECT & LVPDIS);	// freq. clock 4MHz
//__CONFIG(WDTDIS & HS & UNPROTECT & LVPDIS);	// freq. clock 20MHz


#define PORTBIT(adr, bit) ((unsigned)(&adr)*8+(bit))

static bit CSL @ PORTBIT(PORTA, 0);
static bit CSR @ PORTBIT(PORTA, 1);
static bit BLK @ PORTBIT(PORTA, 2);
static bit CLK @ PORTBIT(PORTA, 3);
static bit DAT @ PORTBIT(PORTA, 5);

static bit ST1 @ PORTBIT(PORTB, 5);
static bit ST0 @ PORTBIT(PORTB, 4);
static bit VUP @ PORTBIT(PORTC, 7);
static bit VDW @ PORTBIT(PORTC, 6);


#ifndef	XTAL_FREQ
#define	XTAL_FREQ	4MHZ		/* Crystal frequency in MHz */
#endif

#define	MHZ	*1000L			/* number of kHz in a MHz */
#define	KHZ	*1			/* number of kHz in a kHz */

#if	XTAL_FREQ >= 12MHZ
	#define	DelayUs(x)	{ unsigned char _dcnt; \
				  _dcnt = (x)*((XTAL_FREQ)/(12MHZ)); \
				  while(--_dcnt != 0) \
				  continue; }
#else
	#define	DelayUs(x)	{ unsigned char _dcnt; \
				  _dcnt = (x)/((12MHZ)/(XTAL_FREQ))|1; \
				  while(--_dcnt != 0) \
					  continue; }
#endif

void DelayMs(unsigned char cnt);
void write_SPI(unsigned int data, unsigned int len);


#define MAX_VOL	(1023)
#define INC_VOL (1)

void main()
{
    int  i, flag = 1;
    unsigned char buf, curr, SAVEPOR;
    int vol = 0, mod_lev = 0, auto_incr = 1;

	
    TRISA   = 0b00000000;  // All ports A are output
    TRISB   = 0b00110000;  // Only Rb4 and 5 are input
    TRISC   = 0b11000000;  // Only Rc6 and 7 are input
	
    ADCON1  = 0x06;	   // All posts AN4-7 to digital

    PORTA = 0b00000000;

    CSL = 1;
    CSR = 1;
    DAT = 0;
    CLK = 0;

    //##################################################
    //# wait 1 second for power supply startup
    //##################################################
    BLK = 0;
    DelayMs(250);
    BLK = 1;
    DelayMs(250);
    BLK = 0;
    DelayMs(250);
    BLK = 1;
    DelayMs(250);

    //##################################################
    //# set the AD1955 in mono mode
    //##################################################
    CSL = 0;
    write_SPI(0b00001100, 8);
    write_SPI(0b00000000, 8);
    CSL = 1;
 
    DelayMs(5);

    CSR = 0;
    write_SPI(0b00001000, 8);
    write_SPI(0b00000000, 8);
    CSR = 1;
    

    while(1)
    {
        if (VUP == 0)
        {
            if (vol < MAX_VOL)
            {
                if (vol < (MAX_VOL - INC_VOL))
		    vol += INC_VOL;
                else
                    vol = MAX_VOL;
            }
	    mod_lev   = 1;
	    auto_incr = 0;
	}
        if (VDW == 0)
        {
            if (vol > 0)
            {
                if (vol > INC_VOL)
		    vol -= INC_VOL;
                else
                    vol = 0;
            }
	    mod_lev   = 1;
	    auto_incr = 0;
	}
	if (auto_incr == 1 || mod_lev == 1)
	{
	    //##################################################
	    //# set the AD1955 volume
	    //################################################## 	
	    CSR = 0;
	    CSL = 0;
	    write_SPI(vol, 10);
	    write_SPI(0b1111, 4);
	    write_SPI(0b11, 2);
	    CSR = 1;
	    CSL = 1;

	    CSR = 0;
	    CSL = 0;
	    write_SPI(vol, 10);
	    write_SPI(0b1111, 4);
	    write_SPI(0b10, 2);
	    CSR = 1;
	    CSL = 1;

	    if (auto_incr == 1)
	    {
		if (vol == MAX_VOL)
		    auto_incr = 0;
		else
		    vol++;
	    }
	    DelayMs(1);

	    mod_lev = 0;
	}
    }
}

void write_SPI(unsigned int data, unsigned int n_bit)
{
    unsigned int bit_mask;
    int i;


    bit_mask = 1 << (n_bit - 1);
    
    for (i = 0; i < n_bit; i++)
    {        
        CLK = 0;

	DelayUs(100);

        if ((data & bit_mask) == 0)
            DAT = 0;
        else
            DAT = 1;

	DelayUs(100);

        CLK = 1;
       
        data <<= 1;
    }
}

void DelayMs(unsigned char cnt)
{
#if	XTAL_FREQ <= 2MHZ
    do {
	DelayUs(996);
    } while(--cnt);
#endif

#if    XTAL_FREQ > 2MHZ	
    unsigned char	i;

    do {
	i = 4;

	do {
	    DelayUs(250);
	} while(--i);
    } while(--cnt);
#endif
}