[Sound-open-firmware] [PATCH 1/4] [RFC]DMIC: Add PDM microphones (DMIC) support to DAI

[Seppo Ingalsuo]

On 30.04.2018 23:22, Pierre-Louis Bossart wrote:
>> +/* Calculate scale and shift to use for FIR coefficients. Scale is 
>> applied
>> + * before write to HW coef RAM. Shift will be programmed to HW 
>> register.
>> + */
>> +static int fir_coef_scale(int32_t *fir_scale, int *fir_shift, int 
>> add_shift,
>> +    const int32_t coef[], int coef_length, int32_t gain)
>> +{
>> +    int32_t amax;
>> +    int32_t new_amax;
>> +    int32_t new_scale;
>> +    int32_t fir_gain;
>> +    int shift;
>> +    const int32_t coef_max_val = Q_CONVERT_FLOAT(0.9999, 20); /* 
>> Q1.20 */
>> +
>> +    /* Multiply gain passed from CIC with output full scale, result 
>> Q4.20 */
>> +    fir_gain = Q_MULTSR_32X32((int64_t)gain, DMIC_HW_SENS_Q23, 20, 
>> 23, 20);
>> +
>> +    /* Find the largest FIR coefficient value */
>> +    amax = find_max_abs_int32((int32_t *)coef, coef_length);
>> +
>> +    /* Scale with FIR gain */
>> +    new_amax = Q_MULTSR_32X32((int64_t)amax, fir_gain, 31, 20, 20);
>> +    if (new_amax <= 0)
>> +        return -EINVAL;
>> +
>> +    /* Needed scale for FIR taps, target is 0.9999 max */
>> +    new_scale = (int32_t)((((int64_t)coef_max_val << 20)) / new_amax);
>> +
>> +    /* Find shift value */
>> +    if (new_scale == 0)
>> +        return -EINVAL;
>> +
>> +    shift = 0;
>> +    while ((new_scale << shift) < (1 << 20))
>> +        shift++;
>
> don't we have some sort of macro for this (find number of leading 
> zeroes)? 

I rewrote this function partially since I noticed I can do the same 
without the division. The shift value can be calculated from the newly 
made norm_int32(new_amax) function output.

The other larger change is that I updated the modes search struct to use 
int16_t arrays to save RAM.

It took me some time to test these but I'll email shortly the new RFC 
patch set!

Thanks,
Seppo