Make RTC prescaler uint32

[me21]

The RTC prescaler register allows 20 bits wide values to be written, whereas RTClock library uses uint16 for prescaler argument:

Arduino_STM32/STM32F1/libraries/RTClock/src/RTClock.h

Line 44 in 8fa6bb4

RTClock(rtc_clk_src src, uint16 prescaler );

My device has 12 MHz crystal. The prescaler should be 93749 (12000000/128) in my case, but it won't fit into uint16 argument.
The underlying rtc_set_prescaler_load function, which is used internally, already uses uint32 argument.
Please update the library to use uint32 instead.

[rogerclarkmelbourne]

Can you do a PR for this?

[rogerclarkmelbourne]

BTW.
It looks like you need to change RTClock.h and RTClock.cpp because the low level api function

already takes 32 bits and seems to send write it into 2 separate registers in 16 bit chunks

Arduino_STM32/STM32F1/libraries/RTClock/src/utility/rtc_util.c

Lines 197 to 206 in 083e988

	void rtc_set_prescaler_load(uint32 value) {
	rtc_clear_sync();
	rtc_wait_sync();
	rtc_wait_finished();
	rtc_enter_config_mode();
	RTC->regs->PRLH = (value >> 16) & 0xffff;
	RTC->regs->PRLL = value & 0xffff;
	rtc_exit_config_mode();
	rtc_wait_finished();
	}

[me21]

Yeah, I totally agree. I will make a PR, I already have made the changes locally.

[me21]

@rogerclarkmelbourne Please take a look.