Posted on April 03, 2016 at 05:04To MCD Application Team and any professional,
I read through the source code of \STM32Cube_FW_F4_V1.10.0\Drivers\BSP\STM32F411E-Discovery\stm32f411e_discovery_audio.c
as well as any stm32f4xx_audio.c file.
I notice that in function BSP_AUDIO_OUT_Init(), the I2SCLK is set different for 2 different set of audio frequency, multiple of 8 (8k, 16k, 24k, 32k, etc.) and others (11.025k, 22.050k, 44.1k, etc)
================Source Code============================
if((AudioFreq & 0x7) == 0)
{
/* Audio frequency multiple of 8 (8/16/32/48/96/192)*/
/* PLLI2S_VCO Output = PLLI2S_VCO Input * PLLI2SN = 192 Mhz */
/* I2SCLK = PLLI2S_VCO Output/PLLI2SR = 192/6 = 32 Mhz */
rccclkinit.PeriphClockSelection = RCC_PERIPHCLK_I2S;
rccclkinit.PLLI2S.PLLI2SN = 192;
rccclkinit.PLLI2S.PLLI2SR = 6;
HAL_RCCEx_PeriphCLKConfig(&rccclkinit);
}
else
{
/* Other Frequency (11.025/22.500/44.100) */
/* PLLI2S_VCO Output = PLLI2S_VCO Input * PLLI2SN = 290 Mhz */
/* I2SCLK = PLLI2S_VCO Output/PLLI2SR = 290/2 = 145 Mhz */
rccclkinit.PeriphClockSelection = RCC_PERIPHCLK_I2S;
rccclkinit.PLLI2S.PLLI2SN = 290;
rccclkinit.PLLI2S.PLLI2SR = 2;
HAL_RCCEx_PeriphCLKConfig(&rccclkinit);
}
================END=====================================
What is the purpose for this setting??
Thank you
