Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

RE: Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

Kevin Doss — Tue, 25 Jun 2024 14:55:26 GMT

Thank you, I suspected that might be the case... which is why I opened the ticket.

RE: Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

Naeem Maroof — Tue, 25 Jun 2024 08:56:27 GMT

Hi Kevin,

Maria is out-of-office, and I will communicate with you regarding this ticket. I am relaying to you the response received internally regarding the query.

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The reason for the two frequency bands is purely the limitations in the analog oscillator. The two bands correlate to 44.1 kHz and 48 kHz audio frequencies. We are production trimming these two bands to make sure the oscillator operates as intended.

Using frequencies outside these two ranges are prohibited. This is because there is no guarantee that the PLL can provide correct frequency due to the limited tuning range of the internal VCO.

Meaning, if a customer tries to use 12 MHz, they might be able to do so at the bench, but over temperature, process, and voltage, the PLL will start to fail. We cannot guarantee its accuracy or correct operation.

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Regards,

Naeem

RE: Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

Maria Gilje — Thu, 20 Jun 2024 10:17:44 GMT

The person who can provide the necessary information on the ACLK frequency is not available this week. When they are back and has provided us with an explanation we will update you. This will likely be done by Tuesday next week.
Thank you for your patience.

Best regards,
Maria

RE: Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

Kevin Doss — Wed, 19 Jun 2024 16:40:46 GMT

46875 samples per second is a proprietary solution. It's convenient for solutions where the main frequency reference in the system is 24 MHz (or a multiple thereof).

RE: Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

Maria Gilje — Wed, 19 Jun 2024 12:35:44 GMT

We have no guarantee for the device functionality if you go outside the SoC or protocol specification.

A sampling rate of 46875 is not within the LE Audio specification, so if you go forward with that it will be a proprietary solution.

I have not found the right person to ask about the reasoning for the two clock frequency bands for the ACLK yet.

RE: Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

Kevin Doss — Tue, 18 Jun 2024 21:09:31 GMT

FYI, I tried setting HFCLK.FREQUENCY = 0x8000 and configuring the I2S peripheral to operate using ACLK @12 MHz and LRCLK @ 46875 (ACLK/256). The clocks appear to be at the right frequency and stable on my devkit, but what I need to know is if this will always be true or am I just getting lucky on this particular device?

RE: Can ACLK be tuned to 12.0 MHz by setting HFCLKAUDIO.FREQUENCY to 0x8000?

Maria Gilje — Tue, 18 Jun 2024 12:37:25 GMT

Hello,

I want to let you know that I'm working on finding an answer to your questions. Thank you for your patience.

Best regards,

Maria