dedicated clocks configuration register
| USART1SEL | USART 1 clock source selection |
| USART2SEL | USART 2 clock source selection |
| USART3SEL | USART 3 clock source selection |
| UART4SEL | UART 4 clock source selection |
| UART5SEL | UART 5 clock source selection |
| USART6SEL | USART 6 clock source selection |
| UART7SEL | UART 7 clock source selection |
| UART8SEL | UART 8 clock source selection |
| I2C1SEL | I2C1 clock source selection |
| I2C2SEL | I2C2 clock source selection |
| I2C3SEL | I2C3 clock source selection |
| I2C4SEL | I2C4 clock source selection |
| LPTIM1SEL | Low power timer 1 clock source selection |
| CECSEL | HDMI-CEC clock source selection |
| CK48MSEL | 48MHz clock source selection |
| SDMMCSEL | SDMMC clock source selection |