zephyr/boards/arm/nucleo_f091rc/nucleo_f091rc_defconfig

# Zephyr Kernel Configuration
CONFIG_ARM=y
CONFIG_SOC_SERIES_STM32F0X=y

# Platform Configuration
CONFIG_SOC_STM32F091XC=y
CONFIG_BOARD_NUCLEO_F091RC=y

# General Kernel Options
CONFIG_CORTEX_M_SYSTICK=y
CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=48000000

# Serial Drivers
CONFIG_SERIAL=y
CONFIG_UART_INTERRUPT_DRIVEN=y
# enable console
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y

# Pinmux Driver
CONFIG_PINMUX=y

# GPIO Controller
CONFIG_GPIO=y

# Clock configuration
CONFIG_CLOCK_CONTROL=y
# SYSCLK selection
CONFIG_CLOCK_STM32_SYSCLK_SRC_PLL=y
# HSE configuration
CONFIG_CLOCK_STM32_HSE_CLOCK=8000000
# however, the board does not have an external oscillator, so just use
# the 8MHz clock signal coming from integrated STLink
CONFIG_CLOCK_STM32_HSE_BYPASS=y
# PLL configuration
CONFIG_CLOCK_STM32_PLL_SRC_HSE=y
# produce 48MHz clock at PLL output
CONFIG_CLOCK_STM32_PLL_PREDIV1=1
CONFIG_CLOCK_STM32_PLL_MULTIPLIER=6
CONFIG_CLOCK_STM32_AHB_PRESCALER=1
CONFIG_CLOCK_STM32_APB1_PRESCALER=1