USART receiving nonsense (STM32F0) - c

Question

I have an implementation for USART communication from a GPS module to a STM32F091 microcontroller.
For some reason I only receive nonsense. I have already tried setting different Baud Rates, but none gave me a proper result.
Now I am unsure if maybe there is something funky with prescaler settings or something else I forgot.
The relevant code looks as follows:
peripherals.c
/* Clock settings */
void clock_init(void)
{
/* Enable HSI clock */
RCC->CR |= RCC_CR_HSION;
/* Enable clocks on Port A, B, F */
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOB, ENABLE);
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOF, ENABLE);
/* Enable USART clocks */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
}
/* Select Alternate Port Functions */
void alt_init(void)
{
/* Port A: USART1 */
GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_1);
GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_1);
/* Port B: USART3 */
GPIO_PinAFConfig(GPIOB, GPIO_PinSource10, GPIO_AF_4);
GPIO_PinAFConfig(GPIOB, GPIO_PinSource11, GPIO_AF_4);
}
usart.c
USART_InitTypeDef USART_InitStructure;
GPIO_InitTypeDef GPIO_InitStructure;
NVIC_InitTypeDef NVIC_InitStructure;
/* Baud rate */
uint32_t bd = 9600;
void usart_init(void)
{
/* ##################### USART 1 ##################### */
/* USART GPIO Settings */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* USART Settings */
USART_InitStructure.USART_BaudRate = bd;
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_StopBits = USART_StopBits_1;
USART_InitStructure.USART_Parity = USART_Parity_No;
USART_InitStructure.USART_HardwareFlowControl =
USART_HardwareFlowControl_None;
USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
USART_Init(USART1, &USART_InitStructure);
/* Enable USART because it's disabled in USART_Init */
USART_Cmd(USART1, ENABLE);
/* ##################### USART 2 ##################### */
/* ##################### USART 3 ##################### */
/* Disable USART3 in order to use SWAP */
USART_Cmd(USART3, DISABLE);
/* Swap TX and RX pins */
USART3->CR2 |= USART_CR2_SWAP;
/* Enable USART3 */
USART_Cmd(USART3, ENABLE);
/* USART GPIO Settings */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10 | GPIO_Pin_11;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOB, &GPIO_InitStructure);
/* USART Settings */
USART_InitStructure.USART_BaudRate = bd;
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_StopBits = USART_StopBits_1;
USART_InitStructure.USART_Parity = USART_Parity_No;
USART_InitStructure.USART_HardwareFlowControl =
USART_HardwareFlowControl_None;
USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
USART_Init(USART3, &USART_InitStructure);
/* Enable USART because it's disabled in USART_Init */
USART_Cmd(USART3, ENABLE);
/* Enable USART Interrupts */
USART_ITConfig(USART3, USART_IT_RXNE, ENABLE);
USART_ITConfig(USART3, USART_IT_TXE, ENABLE);
/* Enable external interrupts */
NVIC_InitStructure.NVIC_IRQChannel = USART3_8_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
/* ##################### USART 4 ##################### */
}
stm32f0xx_it.c
#include <main.h>
void USART3_8_IRQHandler(void)
{
char t[] = "U";
uint16_t byte = 0;
if (USART_GetFlagStatus(USART3, USART_FLAG_RXNE) != RESET) // Data reception
{
byte = USART_ReceiveData(USART3);
(*pRXD3).Buffer[(*pRXD3).wr] = byte;
(*pRXD3).wr = ((*pRXD3).wr + 1);
USART_SendData(USART1, t[0]);
USART_GetFlagStatus(USART3, USART_IT_ORE);
USART_ClearITPendingBit(USART3, USART_IT_RXNE);
}
return;
}
The USART_SendData bit is for communication with my PC, so I can see if I receive the letter U or more nonesense.
I have also checked the content of the DR register (by way of checking the Buffer I write its content to) of USART3 directly so I know the STM32F091 receives (or rather interperts) my GPS output wrong.
The GPS module uses a default baudrate of 9600 which I do not change.
Let me know if there's any additional info

Answer 1

After a lot of searching and the suggestions of everyone in the comments, I figured out that the System Clock was not set up properly.
The following pieces of code were necessary in addition to what was already in the 'clock_init'.
peripherals.c
/* Clock settings */
void clock_init(void)
{
....
/* Select System Clock to be HSI */
RCC_SYSCLKConfig(RCC_SYSCLKSource_HSI);
/* Select USART clock source to be System Clock */
RCC_USARTCLKConfig(RCC_USART1CLK_SYSCLK);
RCC_USARTCLKConfig(RCC_USART3CLK_SYSCLK);
....
}
Thanks to everyone for the help.