PCM module raspberry pi 3b

//function to init GPIO 18 19 20 21 and set in ALT0 for PCM
static void init_pcm_gpio()
{
    unsigned int FSEL1 = *(volatile unsigned*)GPFSEL1; //GPIO 18 - 19
    unsigned int FSEL2 = *(volatile unsigned*)GPFSEL2; //GPIO 20 - 21

    FSEL1 &= ~((0b111) << 24) | ((0b111) << 27);
    FSEL2 &= ~((0b111) | ((0b111) << 3));

    FSEL1 |= ((0b100 << 24) | (0b100 << 27));
    FSEL2 |= ((0b100) | (0b100 << 3));

    *(volatile unsigned*)GPFSEL1 = FSEL1;
    *(volatile unsigned*)GPFSEL2 = FSEL2;

    *(volatile unsigned*)GPPUD = 0;
    delay(150);
    *(volatile unsigned*)GPPUDCLK0 = (1 << 18 | 1 << 19 | 1 << 20 | 1 << 21);
    delay(150);
    *(volatile unsigned*)GPPUDCLK0 = 0;
}
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//function to choose the good clock to use with the good divider for the Bit clock
static void init_pcm_clock()
{
   *(volatile unsigned*)CM_PCMCTL = CM_PASSWORD | 0x1; 
    while ( *(volatile unsigned*)CM_PCMCTL & 0x80); //wait busy

    //DIVI = 13, DIVF = 2480
    //Password | (DIVI << 12) | DIVF
    *(volatile unsigned*)CM_PCMDIV = CM_PASSWORD | (13 << 12) | 2480;

    // Source: 1 (OSC), MASH: 1 (pour le fractionnaire), ENAB: 1
    *(volatile unsigned*)CM_PCMCTL = CM_PASSWORD | (1 << 9) | (1 << 4) | 0x1;
}

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//function to init the PCM module and set all hardware register

static void init_pcm()
{
    /* Disable PCM */
    *(volatile unsigned*)PCM_CS_A = 0; 

    unsigned mode_a = 0;

    mode_a &= ~(1 << 28); //enable PCM clock
    mode_a &= ~(1 << 23); //Master PCM Mclock
    mode_a &= ~(1 << 21); //Master PCM Fclock
    mode_a |= (31 << 10); //number of clock need (31+1)
    mode_a |= (16 << 0);  //nombre de clock

    *(volatile unsigned*)PCM_MODE_A = mode_a;

    unsigned tx_a = 0;

    tx_a |= (1 << 30);  //enable chanel 1
    tx_a |= (8 << 16);   //width of 16bits for chanel 1
    tx_a |= (0 << 20);  //position 0

    tx_a |= (1 << 14); //enable chanel 2
    tx_a |= (8 << 0);   //width of 16bits for chanel 2
    tx_a |= (16 << 4);  //position of the value to chanel 2 to send

    *(volatile unsigned*)PCM_TXC_A = tx_a;

    unsigned cs_a = 0;

    cs_a |= 1 << 2; //enable transimission
    cs_a |= 1;      //enable PCM module

    *(volatile unsigned*)PCM_CS_A = cs_a;
}

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//function to fill the FIFO if it is not full

void send_data_to_pcm(unsigned data) {
    if ((*(volatile unsigned*)PCM_CS_A) & (1 << 19))    //FIFO not full
        *(volatile unsigned *)PCM_FIFO_A = data;
}

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//kernel main to send data in the FIFO of the PCM

init_I2S();
	//enable_irq();
    printf("kernel boots...\r\n");

	unsigned cptr = 0;

	while (1){
		printf("loop..\r\n");
		
		if ((cptr & 1) == 0) {
			send_data_to_pcm(0xFFFF);
		} else {
			send_data_to_pcm(0x0);
		}
		cptr++;
	}