Bare metal USART2 clock speed question

[STMnoob]

Hello,

I am learning bare metal programming for STM32F446RE and am trying to write a simple transmit driver for USART2. I managed to do it but my only problem is when I use HSI 16Mhz clock speed (or anything lower) I get a weird first character. When I use a higher clock speed it works fine (using another clock source). 

Does anyone know the reason for that?

Thank you

void USART_init(){
	RCC->APB1ENR|=(1<<17);

	USART2->CR1&=~(1<<12);
	USART2->CR1&=~(1<<10);
	USART2->CR1&=~(1<<15);

	USART2->CR1|=(1<<13);

	// Baud Rate of 115200 and Clock of 16Mhz
	USART2->BRR=(8<<4 | 11);

	USART2->CR1|=(1<<3);
	USART2->CR1|=(1<<2);

	char g[15];
	sprintf(g,"Hello\r\n");

	for(int i=0;i<strlen(g);i++){
		while(!(USART2->SR & (1<<7)));
		USART2->DR=g[i];
	}

	while(!(USART2->SR & (1<<6)));