How to set PDM gain

RE: How to set PDM gain

Aaron F — Tue, 02 Jan 2024 15:15:00 GMT

Hi Jeffrey,

The way we solved this was to call the the nrf_pdm_gain_set() between the calls to dmic_configure() and dmic_trigger().

        ret = dmic_configure(m_dmic_dev, &m_dmic_cfg);
        if (ret < 0) {
            LOG_ERR("Failed to configure the driver: %d", ret);
            return ret;
        }
#ifdef NRF_PDM0_S
        // nRF5340
        nrf_pdm_gain_set(NRF_PDM0_S, NRF_PDM_GAIN_MAXIMUM, NRF_PDM_GAIN_MAXIMUM);
#else
        // nRF52840
        nrf_pdm_gain_set(NRF_PDM, NRF_PDM_GAIN_MAXIMUM, NRF_PDM_GAIN_MAXIMUM);
#endif
        ret = dmic_trigger(m_dmic_dev, DMIC_TRIGGER_START);
        if (ret < 0) {
            LOG_ERR("START trigger failed: %d", ret);
            return ret;
        }

RE: How to set PDM gain

Jared — Tue, 05 Dec 2023 10:27:50 GMT

[quote user="jefffhaynes"]I just ran into this same problem. Would there be anything wrong with simply setting the gain registers after driver initialization?[/quote]

If it doesn't result in an error it's probably fine, but..

In general you should either use nrfx driver or zephyr driver. It's best not to mix the usage of both at the same time in the application code, as zephyr is using the nrfx driver and mixing both might add some redundant code or an error, for example if a function should only be called once per initialization etc.

PDM gain is set in the nrfx driver here,

regards

Jared

RE: How to set PDM gain

Jeffrey Haynes — Tue, 05 Dec 2023 03:50:18 GMT

I just ran into this same problem. Would there be anything wrong with simply setting the gain registers after driver initialization?

RE: How to set PDM gain

ovrebekk — Thu, 09 Nov 2023 13:39:11 GMT

You are not overlooking anything, no. The dmic example is quite generic and doesn't expose any functionality unique to the Nordic PDM peripheral.

In order to get full control over the PDM peripheral the best option is probably to use the nrfx_pdm driver directly, or to spin your own PDM driver based on the dmic_nfrx_pdm implementation.

The nrfx configuration is set in the code here, and you could always add some lines to set the gain_l and gain_r fields of the nrfx_cfg struct before the nrfx_pdm driver is initialized.

Best regards
Torbjørn