i2s_at91.c

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#include "i2s_at91.h"

#include <drv/timer.h>
#include <cfg/log.h>
#include <io/arm.h>

#define DATALEN (15 & SSC_DATLEN_MASK)
// FIXME: this is not correct for 16 <= DATALEN < 24
#define PDC_DIV ((DATALEN / 8) + 1)
/* PDC_DIV must be 1, 2 or 4, which are the bytes that are transferred
 * each time the PDC reads from memory.
 */
STATIC_ASSERT(PDC_DIV % 2 == 0);
#define PDC_COUNT (CONFIG_PLAY_BUF_LEN / PDC_DIV)

static uint8_t play_buf1[CONFIG_PLAY_BUF_LEN];
static uint8_t play_buf2[CONFIG_PLAY_BUF_LEN];

// the buffer in PDC next is play_buf2
volatile bool is_second_buf_next;

uint8_t *i2s_getBuffer(unsigned buf_num)
{
    LOG_INFO("getBuffer start\n");

    if (i2s_isPlaying())
    {
        ASSERT(0);
        return 0;
    }

    if (buf_num == I2S_SECOND_BUF)
        return play_buf2;
    else if (buf_num == I2S_FIRST_BUF)
        return play_buf1;
    else
        return 0;
}

uint8_t *i2s_getFreeBuffer(void)
{
    if (!i2s_isPlaying())
    {
        ASSERT(0);
        return 0;
    }

    // wait PDC transmission end
    if (!(SSC_SR & BV(SSC_ENDTX)))
        return 0;

    uint8_t *ret_buf = 0;
    // the last time we got called, the second buffer was in PDC next
    if (is_second_buf_next)
    {
        is_second_buf_next = false;
        ret_buf = play_buf1;
    }
    // the last time the first buffer was in PDC next
    else
    {
        is_second_buf_next = true;
        ret_buf = play_buf2;
    }

    if (ret_buf)
    {
        SSC_TNPR = (reg32_t) ret_buf;
        SSC_TNCR = PDC_COUNT;
    }
    return ret_buf;
}

bool i2s_start(void)
{
    /* Some time must pass between disabling and enabling again the transmission
     * on SSC. A good empirical value seems >15 us. We try to avoid putting an
     * explicit delay, instead we disable the transmitter when a sound finishes
     * and hope that the delay has passed before we enter here again.
     */
    SSC_CR = BV(SSC_TXDIS);
    timer_delay(10);

    SSC_PTCR = BV(PDC_TXTDIS);
    SSC_TPR = (reg32_t)play_buf1;
    SSC_TCR = PDC_COUNT;
    SSC_TNPR = (reg32_t)play_buf2;
    SSC_TNCR = PDC_COUNT;
    is_second_buf_next = true;

    SSC_PTCR = BV(PDC_TXTEN);

    /* enable output */
    SSC_CR = BV(SSC_TXEN);

    return true;
}

#define BITS_PER_CHANNEL 16
#define N_OF_CHANNEL 2
// TODO: check the computed value?
/* The last parameter (2) is due to the hadware on at91sam7s. */
#define MCK_DIV (CPU_FREQ / CONFIG_SAMPLE_FREQ / BITS_PER_CHANNEL / N_OF_CHANNEL / 2)

#define CONFIG_DELAY 1
#define CONFIG_PERIOD 15
#define CONFIG_DATNB  1
#define CONFIG_FSLEN 15

#define DELAY ((CONFIG_DELAY << SSC_STTDLY_SHIFT) & SSC_STTDLY_MASK)
#define PERIOD ((CONFIG_PERIOD << (SSC_PERIOD_SHIFT)) & SSC_PERIOD_MASK)
#define DATNB ((CONFIG_DATNB << SSC_DATNB_SHIFT) & SSC_DATNB_MASK)
#define FSLEN ((CONFIG_FSLEN << SSC_FSLEN_SHIFT) & SSC_FSLEN_MASK)

#define SSC_DMA_IRQ_PRIORITY 5

void i2s_init(void)
{
    PIOA_PDR = BV(SSC_TK) | BV(SSC_TF) | BV(SSC_TD);
    /* reset device */
    SSC_CR = BV(SSC_SWRST);

    SSC_CMR = MCK_DIV & SSC_DIV_MASK;
    SSC_TCMR = SSC_CKS_DIV | SSC_CKO_CONT | SSC_CKG_NONE | DELAY | PERIOD | SSC_START_FALL_F;
    SSC_TFMR = DATALEN | DATNB | FSLEN | BV(SSC_MSBF) | SSC_FSOS_NEGATIVE;

    /* Disable all irqs */
    SSC_IDR = 0xFFFFFFFF;

    /* Enable the SSC IRQ */
    AIC_IECR = BV(SSC_ID);

    /* enable i2s */
    PMC_PCER = BV(SSC_ID);

    /* Enable SSC */
    SSC_CR = BV(SSC_TXEN);
}