nrf52840dk PCA10056 I2S MCLK Ratio

RE: nrf52840dk PCA10056 I2S MCLK Ratio

tomatosoup — Tue, 04 Apr 2023 13:02:29 GMT

Ok, I have now found the solution.

Reconfiguring the MCKFREQ register results in a LRCLK/BCLK which isn't correct anymore as they were based on a different calculation.

Thus also setting the register RATIO is necessary.

This code was the solution for 8kHz SR and 256fs:

// 8kHz Sampling Rate
// --
// MCLK = 256 * 8 kHz = 2.048Mhz
// BCLK = 2 * 16 * 8kHz = 256kHz
// --
// CONFIG.MCKFREQ = 32MHz / 16 = 2Mhz -> 0x10000000
// CONFIG.RATIO = 2MHz / 256 = 7.8125kHz -> 6		
*(volatile uint32_t *) 0x40025514 = 0x10000000;
*(volatile uint32_t *) 0x40025518 = 6;

RE: nrf52840dk PCA10056 I2S MCLK Ratio

Kenneth — Tue, 04 Apr 2023 08:00:52 GMT

Seems to work here:

Kenneth

RE: nrf52840dk PCA10056 I2S MCLK Ratio

tomatosoup — Mon, 03 Apr 2023 18:50:10 GMT

Thanks, but somehow this seems to break the I2S Transfer.

Currently, I have hooked up an external 2.048MHz Clock Source to MCLK of my Codec. Doing so, the Echo Example with my modified codec.c works as expected. I have Audio on my Line Out with Echo from the Line In.

As soon as I place your suggested Line after printk("Streams started\n") I don't get any audio anymore.

No matter if I use the MCLK of my external clock source or the MCLK of the nRF.

RE: nrf52840dk PCA10056 I2S MCLK Ratio

Kenneth — Mon, 03 Apr 2023 15:12:50 GMT

You can try: *(volatile uint32_t *) 0x40025514 = 0x10000000;

Kenneth

RE: nrf52840dk PCA10056 I2S MCLK Ratio

tomatosoup — Mon, 03 Apr 2023 14:25:41 GMT

Ok, can you give me a code example to change the MCLK after i2s_configure()?

To my understanding, the nRF Connect SDK I2S driver hooks into the nRF5 SDK. But theres no API to change the MCLK. There is just nrfx_i2s_init(). But this doesn't really help me as I don't have the config object.

RE: nrf52840dk PCA10056 I2S MCLK Ratio

Kenneth — Mon, 03 Apr 2023 12:37:28 GMT

Looking quickly at the implementation of find_suitable_clock() in i2s_nrfx.c it looks to just choose one that fits, so if you need a specific MCLK I suggest to set it manually after i2s_configure() yes.

Kenneth

RE: nrf52840dk PCA10056 I2S MCLK Ratio

tomatosoup — Mon, 03 Apr 2023 10:47:10 GMT

Hi,

Thanks for your Answer.

Can you explain me on how I can set it to 2MHz in nRF Connect SDK? Do I need to write the Register directly?

Currently, I'm using this example which I would like to reconfigure to 2MHz: github.com/.../echo

RE: nrf52840dk PCA10056 I2S MCLK Ratio

Kenneth — Mon, 03 Apr 2023 10:07:09 GMT

Hello,

Looking at the Table 1 configuration example I can find that 32MDIV16 equals 2MHz:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/i2s.html

Also see:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/i2s.html#register.CONFIG.MCKFREQ

For Audio you should consider using the nRF5340 which has an Audio PLL (e.g. it can for instance allow dynamic adjustment on the fly):
https://infocenter.nordicsemi.com/topic/ps_nrf5340/i2s.html

Best regards,
Kenneth