Linux/AM3358: McASP dts how is the bit clock set

Mohsen Khayami

Part Number: AM3358

Tool/software: Linux

I like to understand how is the direction, the speed , and the source of the ACLKx (the bit clock) is set?

I would imagine the direction is set by the pin mux defined if output or input . I would imagine if you wanted to use an external clock for the MCASP then you would have the AHCLK as input then that way you can use it as to generate the bit clock.

But I still don't understand the source of the clock and the speed? Any examples would help a bunch.

Thanks

Regards

Mohsen

over 6 years ago

0 Pavel Botev over 6 years ago

TI__Guru**** 170625 points

Hi Mohsen,

These ACLKx bit clock parameters (direction, speed, source) depends on who is the master. If master is the audio codec, then ACLKx bit clock is input and sourced by audio codec BCLK out pin. If master is AM335x McASP module, then ACLKx bit clock is output and generated by main clock osc CLK_M_OSC or AHCLKX input pin. Master or slave of ACLKx is selected by below DTS parameter:

simple-audio-card,bitclock-master = <&sound_master>;

If master is AM335x McASP module, we have:

sound_master: simple-audio-card,cpu

If master is audio codec, we have:

sound_master: simple-audio-card,codec

The speed is configured dynamically, it depends on what speed/frequency/rate value is passed to alsa tool (arecord/aplay) or used in alsa application. Then this speed/frequency/rate value is applied to McASP registers (if McASP is master).

You can refer to below documents for better understanding, there are also examples in these docs.

AM335x TRM, sections 22.3.5 Clock and Frame Sync Generators and 22.3.5.1 Transmit Clock

www.ti.com/.../sprack0.pdf
www.ti.com/.../sprac97.pdf
www.ti.com/.../sprac09a.pdf
www.ti.com/.../sprac10.pdf

software-dl.ti.com/.../Foundational_Components_Kernel_Drivers.html

processors.wiki.ti.com/.../AM335x_Audio_Driver's_Guide

Regards,
Pavel

0 Mohsen Khayami over 6 years ago in reply to Pavel Botev

TI__Mastermind 22391 points

Thanks Pavel
I missed the section on the sound in the DTS. That answers my question

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Linux/AM3358: McASP dts how is the bit clock set