board: nucleo_l152re: Limit sysfreq to 16MHz

A bug under investigation (issue zephyrproject-rtos#22078) limits board operations
to 16MHz. When running at 32MHz, some applications may crash.

In order to enable use of nucleo_l152re with mot of applications,
limit frequency to 16MHz until bug is fixed.


Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>

boards/arm/nucleo_l152re/doc/index.rst

@@ -94,6 +94,13 @@ Other hardware features are not yet supported in this Zephyr port.
 The default configuration can be found in the defconfig file:
 ``boards/arm/nucleo_l152re/nucleo_l152re_defconfig``
 
+System Clock
+============
+
+Nucleo L152RE System Clock could be driven by internal or external oscillator,
+as well as main PLL clock. It should theoretically support running at 32MHz,
+but a bug (under investigation) limits operations to 16MHz.
+
 Connections and IOs
 ===================
 

boards/arm/nucleo_l152re/nucleo_l152re_defconfig

@@ -5,7 +5,7 @@ CONFIG_SOC_SERIES_STM32L1X=y
 CONFIG_SOC_STM32L152XE=y
 CONFIG_CORTEX_M_SYSTICK=y
 # 32MHz system clock
-CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=32000000
+CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=16000000
 
 # enable uart driver
 CONFIG_SERIAL=y
@@ -25,7 +25,7 @@ CONFIG_CLOCK_CONTROL=y
 CONFIG_CLOCK_STM32_SYSCLK_SRC_PLL=y
 # Use HSI source
 CONFIG_CLOCK_STM32_PLL_SRC_HSI=y
-CONFIG_CLOCK_STM32_PLL_DIVISOR=2
+CONFIG_CLOCK_STM32_PLL_DIVISOR=4
 # produce 32Mhz clock at PLL output
 CONFIG_CLOCK_STM32_PLL_MULTIPLIER=4
 CONFIG_CLOCK_STM32_AHB_PRESCALER=1