Connect clock input to MCLK of I2S communication

I am trying to output I2S communication out from apalis imx6 using linux bsp V2.6

I have a differential MCLK signal coming in to TS_DIFF13+ and TS_DIFF13- (pins 133 and pins 131 respectively)

Where on the SOM can I change in software to use this signal as the master clock for I2S output?




I have a differential MCLK signal coming in to TS_DIFF13+ and TS_DIFF13- (pins 133 and pins 131 respectively)

You cannot.

Pins 133 and 131 go to the PCIe subsystem and serve the PCIe clocking. I don’t know if the i.MX6 HW allows to output an arbitrary frequency on those pins but I’m sure there is no driver available which would allow you to configure such thing should it be needed.

The MCLK usually is a clock which goes to the codec and not considered part of the I2S communication.
I usually recommend to use an external oscillator for an external Audio Codec. One less high speed signal to route.
You could use pin 194 DAP1_MCLK as a MCLK ouput should you chose to use the module as a clock source.
Note that the CCM_CLKO1 function is also used on another pin for the on module codec. So on top of the limited different frequencies that the i.MX 6 can generate for CLKO1 you’re further limited to 24MHz that we need for the internal codec.


P.S. Is there a reason why you want to use an I2S on the UART3/UART4 pins rather than taking the pins which in the Apalis standard are meant for that purpose. i.e. 194/196/198/200/202/204. Should you ever want to use another member of the Apalis family chances are much higher that your carrier board does not need a redesign that way.

The following resources might be usefull:
Apalis iMX 6 Datasheet
Carrier Board Design
Apalis Family Whitepaper

Hi Max,

Thanks for this information. That’s a good question regarding the apalis standard pins - I’ll have to ask our HW eng to see if there was a specific purpose to that choice. In the meantime, and I can ask this is a seperate question if you’d prefer, but would it be in the device tree I would define UART3/UART4 as the I2S output for the time being?

The device-tree is were you would do the pinmuxing, add the HW configuration of the codec (e.g. tell the kernel its i2c address) and match the codec driver with the i2s driver.