C8051f120 SPI use

Hello,

I want to use SPI bus to control a VGA (Variable Gain Amplifier). I'm using a DAC between the C8051F120 micro-controller and the VGA. I want to control the input voltage of the VGA, so the output voltage of the DAC. To control this, I'm using too two push-button to increment or decrement the output voltage of the DAC. I've maked the source code but there are some problems about the SPI outputs and the interrupts /INT0 and /INT1. Here my progam:

//------------------------------------------------------------------------------
//       Includes
//------------------------------------------------------------------------------

#include <stdio.h>
#include <c8051f120.h>     // SFR declarations


//------------------------------------------------------------------------------
//       Global constants
//------------------------------------------------------------------------------

#define DAC     16      // 10000 in binary

sbit SPI_SCLK=P0^2;     // SPI clock on P0.2
sbit SPI_MISO=P0^3;     // Master In/Slave Out on P0.3
sbit SPI_MOSI=P0^4;     // Master Out/Slave In on P0.4
sbit SPI_NSS=P0^5;      // Slave Select on P0.5

sbit INC=P1^0;          // /INT0 interrupt on P1.0
sbit DEC=P1^1;          // /INT1 interrupt on P1.1
sbit TEST=P2^0;

//------------------------------------------------------------------------------
//       Global variables
//------------------------------------------------------------------------------

int valeur = 0;      // transfert data

//------------------------------------------------------------------------------
//       Functions prototypes
//------------------------------------------------------------------------------

void clk_init (void);
void port_init (void);
void config_SPI (void);
void transfert_donnees (int donnee);
void interupt_decrement (void);
void interupt_increment (void);

//------------------------------------------------------------------------------
//       Main
//------------------------------------------------------------------------------

void main (void)
{
        clk_init ();
    port_init ();
    config_SPI ();

        transfert_donnees (valeur);

     while (1)
     {

     }

}

//------------------------------------------------------------------------------
//     Clock Initialisation
//------------------------------------------------------------------------------

void clk_init (void)
{
        int i;

        char sfrpage_save = SFRPAGE;        // Save current page of SFR
        SFRPAGE = CONFIG_PAGE;              // Load config_page


        OSCXCN = 0x67;         // Start external oscillator with 22.1184MHz crystal
        for(i=0; i < 256; i++);             // Wait for the oscillator to start up
        while(!(OSCXCN & 0x80));
        CLKSEL = 0x01;
        OSCICN = 0x00;
        SFRPAGE = CONFIG_PAGE;
        PLL0CN = 0x04;
        SFRPAGE = LEGACY_PAGE;
        FLSCL = 0x10;
        SFRPAGE = CONFIG_PAGE;
        PLL0CN |= 0x01;
        PLL0DIV = 0x04;
        PLL0FLT = 0x01;
        PLL0MUL = 0x09;
        for(i=0; i < 256; i++);
        PLL0CN |= 0x02;
        while(!(PLL0CN & 0x10));
        CLKSEL = 0x02;

        SFRPAGE = sfrpage_save;             // Restore SFR page

}

//------------------------------------------------------------------------------
//     Ports I/O initialisation
//------------------------------------------------------------------------------

void port_init (void)
{
         char sfrpage_save = SFRPAGE;     // Save current page of SFR

     SFRPAGE = CONFIG_PAGE;           // Load config_page

     EA   = 1;                        // Enable all interrupts
         TCON = 0x0F;                     // Enable extern interrupts

         WDTCN = 0xde;
         WDTCN = 0xad;                    // Disable watchdog timer

     XBR0            = 0x02;          // Enable SPI bus
     XBR1            = 0x14;          // Enable /INT0 and /INT1
     XBR2            = 0x40;          // Enable Crossbar and weak pull-up

         P0MDOUT                |= 0x3C;          // P0.5, P0.4, P0.3 and P0.2 are outputs (for SPI datas)
         P0                              = 0x3C;
         P1MDIN         &= 0x03;          // P1.0 and P1.1 are inputs (for interrupts)


         EX0 = 1;
         EX1 = 1;

     SFRPAGE = sfrpage_save;          // Restore SFR page
}

//------------------------------------------------------------------------------
//     SPI bus configuration
//------------------------------------------------------------------------------

void config_SPI (void)
{
     char sfrpage_save = SFRPAGE;     // Save current SFR page

     SFRPAGE = SPI0_PAGE;             // Load SPI page

     SPI0CFG |= 0x40;                 // Master Mode Enable
     SPI0CN  |= 0x89;                 // Slave select and enable SPI
     SPI0CKR  = 0x00;                 // SYSCLK/2

     SFRPAGE = sfrpage_save;          // Restore SFR page

}

//------------------------------------------------------------------------------
//     Data transfert
//------------------------------------------------------------------------------

void transfert_donnees (int data)
{
     unsigned char data_1;
     unsigned char data_2;

     data_1 = ( data & 0xFF00) >> 8;     // MSB in data_1
     data_2 = ( data & 0x00FF);          // LSB in data_2

     SPI0DAT = data_1;                   // data_1 transmission
         SPIF    = 0;
         SPI0DAT = data_2;                   // data_2 transmission
         SPIF    = 0;

}
//------------------------------------------------------------------------------
// Interrupt routines
//------------------------------------------------------------------------------

//------------------------------------------------------------------------------
//      /INT0 interrupt
//------------------------------------------------------------------------------

void interupt_increment (void) interrupt 0
{

     if ( valeur >= 1200)
     {
          valeur = 1200;             // Stability at 1200
     }

     else
     {
          valeur = valeur + DAC;     // increment of 10000 (binary)
     }

         transfert_donnees (valeur);

}

//------------------------------------------------------------------------------
//    /INT1 interrupt
//------------------------------------------------------------------------------

void interupt_decrement (void) interrupt 2
{

     if ( valeur <= 0)
     {
          valeur = 0;               // Not negative;
     }

     else
     {
         valeur = valeur - DAC;     // decrement of 10000 (binary)
     }

        transfert_donnees (valeur);

}

Help me please.

Thanks