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AM335x - alternative McASP functional clock source (i.e. not CLK_M_OSC)

mark_
Prodigy 60 points
Other Parts Discussed in Thread: AM3354

Hi,

Based on the AM335x TRM the McASP functional clock is called "PD_PER_MCASP_FCLK" or "Aux Clock" (Page  3949) and is sourced from the PRCM which is sourced from CLK_M_OSC (which is 24MHz on my customer's board). I am wondering if there is a way to either source the McASP functional clock from an alternative clock source (such as a PLL) or do a fractional divide on the Aux Clock? Pg. 3961 indicates that there _might_ be a mechanism to do a fractional divide: "Both the AUXCLK and System Clock are generated from SYSCLK2 (CLKDIV6 domain)." however CLKDIV6 does not appear to be documented.

The issue is that a 24MHz Aux clock can only produce nonstandard frame rates such as 44.117kHz, 50kHz, etc. since the frame rate is calculated like so:

CLK_M_OSC frequency (24MHz) / number of channels (2 for I2S) / channel size (16 for I2S) / (AHCLKX divider + ACLKX divider, both are integers)

Thanks,

Mark

  • 0
    TI__Guru* 86180 points

    Hi Mark,

    There are no fractional divide on the mcasp functional clock.  The best you can do is 24Mhz/544 = 44.117, and 24MHz/500 = 48KHz with a system clock of 24MHz.  You can optionally bring in an external clock through AHCLKX/R pins.  Unfortunately, there are no other choices for the mcasp functional clock. 

     

    Regards,

    James

     

  • 0 in reply to JJD
    Prodigy 60 points

    Thanks James!

    Unfortunately 48kHz is not possible since the customer is using I2S format (i.e. divider of 500 would not be achievable). I'll see if a 44.117kHz sample rate is usable otherwise I'll check if CLKOUT2 could be configured to drive a high frequency audio clock.

    Mark

  • 0 in reply to mark_
    Prodigy 150 points

    HI,

    I need set the sampling rate of 96KHZ using 24MHZ Input clock (CLK_M_OSC) in MCASP0 of AM3354.

    So I need ACLKX as 3.07MHZ, AFSX=96KHZ. I can't generate these exact output clock values of ACLKX and AFSX.

    Kindly suggest the configuration for this.

    Regards,

    R.Mahendra kumar