EmbeddedSystems/EmbeddedSystemsTHM/UART.c

/*
 * UART.c
 *
 * Created: 25/11/2021 16:26:10
 *  Author: n0x
 */ 

#include "UART.h"

/* create structs for TX and TX buffer */
CircularBuffer TxBuffer;
CircularBuffer* pTxBuffer = &TxBuffer;
CircularBuffer RxBuffer;
CircularBuffer* pRxBuffer = &RxBuffer;

volatile uint8_t TxActive;

void 
uart_init(void) {
	UBRR0 = 103;					/* set BAUD rate to 9600 */
	 
	UCSR0C |= 
	(0<<UMSEL00)|(0<<UMSEL01)|		/* Async UART */
	(0<<UPM00)|(0<<UPM01)|			/* Disable Parity */
	(1<<UCSZ00)|(1<<UCSZ01)|		/* 8 Bit */
	(0<<USBS0);						/* 1 Stopbit */
	 	
	UCSR0B |= 
	(1<<TXEN0)|(1<<RXEN0)|			/* enable send and receive */
	(1<<RXCIE0);					/* enable Receive interrupts */	
	
	
	/* Initiate read- and write-pointers with 0 */
	pTxBuffer->Readpointer	= 0;
	pTxBuffer->Writepointer = 0;
	pRxBuffer->Readpointer	= 0;
	pRxBuffer->Writepointer = 0;
}

/********Sending Data********/

void
uart_send_string(char* string) {
	/* Take a whole string and transmit every char from it */
	int i = 0;
	while(string[i] != '\0'){
		uart_send_byte(string[i]);
		i++;
	}
}

void
uart_send_byte(char c) {
	/* Disable the TX Interrupt to prevent issues while writing to the send buffer*/
	UCSR0B &= ~(1<<TXCIE0);
	
	/* Check if a transmit is in progress
	if yes -> write the byte to the buffer
	if no -> write the byte to the UDR0 register and enable the transmit in progress flag 
	*/
	if(TxActive){
		pTxBuffer->data[pTxBuffer->Writepointer++] = c;
		if (pTxBuffer->Writepointer>=SIZE_BUFFER){
			pTxBuffer->Writepointer = 0;
		}
	} else {
		TxActive = 1;
		UDR0 = c;	
	}
	/* Enable the TX Interrupt again*/
	UCSR0B |= (1<<TXCIE0);
}

/* when data (a data frame) is to be send (written to UDR0) */
ISR(USART0_TX_vect) {
	/* check if the read and write pointer of the send buffer are not aligned
	if not aligned -> read the next byte and write it to UDR0 register 
	if aligned -> no more data to send, disable the send in progress flag */
	if(pTxBuffer->Readpointer != pTxBuffer->Writepointer)
	{
		/* writing data to the register withing the interrupt will cause a new interrupt which then will repeat till no more data is to be read from the send buffer */
		UDR0 = pTxBuffer->data[pTxBuffer->Readpointer++];
		
		if(pTxBuffer->Readpointer >= SIZE_BUFFER){
			pTxBuffer->Readpointer = 0;
		}
	} else {
		TxActive = 0;
	}
}

/*******Receiving Data*******/
uint8_t 
uart_data_available(void) {
	uint8_t dataAvailabel = 0;
	/* Disable the RX Interrupt to prevent issues when checking if data is available */
	UCSR0B &= ~(1<<RXCIE0);
	
	/* check if read and write pointer are at different locations
	if yes -> data is available and can be read */
	if(pRxBuffer->Readpointer != pRxBuffer->Writepointer){
		dataAvailabel = 1;
	}
	
	/* Enable the RX Interrupt again*/
	UCSR0B |= (1<<RXCIE0);
	return dataAvailabel;
}

char 
uart_get_data(void) {
	char data = 0;
	/* Disable the RX Interrupt to prevent issues when reading out a char from the buffer */
	UCSR0B &= ~(1<<RXCIE0);
	
	/* check if read and write pointer are at different locations
	if yes -> data is available and can be read */
	if(pRxBuffer->Readpointer != pRxBuffer->Writepointer)
	{
		/* read a char from the buffer and increment the read pointer */
		data = pRxBuffer->data[pRxBuffer->Readpointer++];
		if(pRxBuffer->Readpointer >= SIZE_BUFFER){
			pRxBuffer->Readpointer = 0;
		}
	}
	/* Enable the RX Interrupt again*/
	UCSR0B |= (1<<RXCIE0);
	/* give back the read in character */
	return data;
}

/* when data (a data frame) is received */
ISR(USART0_RX_vect) {
	uint8_t status = UCSR0A;
	uint8_t data = UDR0;
	
	/* check status flags if data is correctly accessible */
	if((status & ((1<<DOR0) | (1<<FE0))) == 0){
		/* Save data to buffer and increment the write pointer */
		pRxBuffer->data[pRxBuffer->Writepointer++] = data;
		if(pRxBuffer->Writepointer >= SIZE_BUFFER) {
			pRxBuffer->Writepointer = 0;
		}
	}
}