Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Keil/AT32F415xx_v2/SPI1/I2SCLK#0x0
I2S clock register
I2S division bit7 to bit0
Odd result for I2S division
I2S master clock output enable
I2S division bit9 and bit8
https://github.com/cmsis-svd/cmsis-svd-data