The clock source selection of LPUART depends on System clocks but also on
the serial baudrate. There is a specific computation done in serial driver
targets/target_STM/serial_api.c
At first start-up the LPUART1 clock selected in SetSysClock was anyway
overridden by the serial driver, so this was of no effect. But in case
of deep sleep SetSysClock is called again, while the driver isn't, so
SetSyClock was corrupting the serial clock configuration.
So let's remove these few lines of code which are causing trouble.
For targets L496 and L5.
Taking into account device TRNG in L5 configuration
Workaround a bug where the boot stack size configuration option is not
passed on to armlink, the Arm Compiler's linker. Prefer
MBED_CONF_TARGET_BOOT_STACK_SIZE if present, as this is what the
configuration system should provide. Fall back to MBED_BOOT_STACK_SIZE
if MBED_CONF_TARGET_BOOT_STACK_SIZE is not defined, as in the case of
buggy tools. If both MBED_CONF_TARGET_BOOT_STACK_SIZE and
MBED_BOOT_STACK_SIZE are not defined, then we fall back to a hard-coded
value provided by the linkerscript. See
https://github.com/ARMmbed/mbed-os/issues/13474 for more information.
To allow overriding of the boot stack size from the Mbed configuration
system, consistently use MBED_CONF_TARGET_BOOT_STACK_SIZE rather than
MBED_BOOT_STACK_SIZE.
Fixes#10319