I2S LRCK FREQ

[Shariff]

Hi, 

I am trying to develop an MP3 player I want to configure LRCK to 44100 but I only able to configure it to 43530 with configuration available in document as CONFIG.RATIO = 32X and CONFIG.MCKFREQ = 32MDIV23.

The exact configuration that I want is CONFIG.RATIO = 256X and CONFIG.MCKFREQ = 32MDIV3. Is there any formula to configure these frequencies since it is not defined in the SDK17.1.0

Thanks and regards.

[Turbo J]

Which codec do you use? Its sometimes simpler to make the codec chip the I²S master, especially if it has a PLL.

The electrical spec in PS limits MCK to 4 MHz maximum, that is why you cannot have a divider smaller than 8 agains the 32 MHz clock source.

Note that I don't think that the NRF52840 will be fast enough for real time MP3 decoding, even the NRF5340 will be at the limit.

I've used minimp3 on a 600 MHz Teensy 4.1, it runs at roughly 50% CPU usage with a high quality MP3 file.

[Shariff]

Hi thanks for the reply.

Now I am able to achieve  LRCK of 44100 but the mp3 audio is playing very fast and I am using fatfs f_read function with buffer size of 512.

And I am copying this buffer and streaming through i2s.

Thanks, and regards.

[Susheel Nuguru]

Ajmal,

Those divisors are from the hardware and only few combinations of LRCK are possible on this hardware.

the closest RATIO I can come up with is 32MDIV15/48 = 44,444

[Shariff]

Hi susheel,

I tried these configurations and now i am getting exact 44.1kHz

RF_I2S_MCK_32MDIV3   = I2S_CONFIG_MCKFREQ_MCKFREQ_32MDIV3,

#define I2S_CONFIG_MCKFREQ_MCKFREQ_32MDIV3 (0x50000000UL)

BR

Ajmal