X-CUBE-SOUNDTER1: how to set I2S clock?

[Marco Perciavalle]

Posted on November 29, 2017 at 22:47

Hi, I have a nucleo f401re board and a x-nucleo-cca01m1 shield mounting STA350BW IC. Nucleo transmits data as a master to the shield using I2S half duplex communication. I want to know what is Master Clock's purpose on I2S bus. I understand that it stands for an external clock for STA350BW, doesn't it? So does the IC work on this clock? 

In particular I want to understand the meaning of these settings referred to the master clock: 

if (AudioFreq == 96000)

{ rccclkinit.PLLI2S.PLLI2SN = 344; rccclkinit.PLLI2S.PLLI2SR = 2; HAL_RCCEx_PeriphCLKConfig(&rccclkinit); } else if (AudioFreq == 48000) { rccclkinit.PLLI2S.PLLI2SN = 258; rccclkinit.PLLI2S.PLLI2SR = 3; HAL_RCCEx_PeriphCLKConfig(&rccclkinit); } else if (AudioFreq == 44100) { rccclkinit.PLLI2S.PLLI2SN = 271; rccclkinit.PLLI2S.PLLI2SR = 2; HAL_RCCEx_PeriphCLKConfig(&rccclkinit); } else if (AudioFreq == 32000) { rccclkinit.PLLI2S.PLLI2SN = 213; rccclkinit.PLLI2S.PLLI2SR = 2; HAL_RCCEx_PeriphCLKConfig(&rccclkinit); }

(x_nucleo_cca01m1_audio_f4.c)

Thanks for any answers. Best regards.

#x-cube-cca01m1 #i2s #nucleo-401 #x-cube-soundter1

[john doe]

Posted on November 30, 2017 at 04:47

N is a multiplier, R is a divisor.  its slowing down the i2s clock when the audio frequency is lower.  plug your values into the STM32CubeMX application's Clock Configuration pane and you can see the changes to the i2s clock frequency.

[Marco Perciavalle]

Posted on November 30, 2017 at 07:23

So the general rule is lower is sampling frequency, slower should be the master clock. Are there amy other constraints? Looking at 

STA350BW's datasheet some internal clock's frequencies are fixed in reference to sampling frequencies. Is there a link with master clock? 

PS in 44800 Hz case, clock seems slower than 44100 Hz case.

Thanks you for the answer