usart.c

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/**
 * @file usart.c
 * @ingroup ccs811
 * @author Jason Duffy
 * @date 15th March 2022
 * @brief Driver file providing core USART communication between the target MCU
 * and your PC.
 * @bug No known bugs. 
 * @see
 */
 
#include <util/setbaud.h>
#include <avr/io.h>
 
#include "usart.h"
 
static void transmit_byte(uint8_t data);
static uint8_t receive_byte(void);
 
 
/*
 * Takes the defined BAUD and F_CPU, calculates the bit-clock multiplier,
 * configures the hardware USART.
 */
void init_usart(void)
{
  // defined in setbaud.h
  UBRR0H = UBRRH_VALUE;
  UBRR0L = UBRRL_VALUE;
 
#if USE_2X
  UCSR0A |= (1 << U2X0);
#else
  UCSR0A &= ~(1 << U2X0);
#endif
  
  // Enable USART transmitter/receiver
  UCSR0B = (1 << TXEN0) | (1 << RXEN0);
  // 8 data bits, 1 stop bit
  UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
}
 
// Utility function to transmit an entire string from RAM.
void print_string(const char myString[])
{
  uint8_t i = 0;
  while (myString[i])
  {
    transmit_byte(myString[i]);
    i++;
  }
}
 
/*
 * Define a string variable, pass it to this function. The string will contain
 * whatever you typed over serial.
 */
void read_string(char myString[], uint8_t maxLength)
{
  char response;
  uint8_t count = 0;
 
  while (count < (maxLength - 1))
  {                  
    response = receive_byte();
    transmit_byte(response); // echo
 
    if (response == '\r') // enter marks the end
    {
      break;
    }
 
    else
    {
      myString[count] = response; // add in a letter
      ++count;
    }
  }
  myString[count] = 0; // terminal NULL character */
}
 
// Prints a byte out as its 3-digit ascii equivalent.
void print_byte(uint8_t byte)
{
  // Converts a byte to a string of decimal text, sends it
  transmit_byte('0' + (byte / 100));            // Hundreds
  transmit_byte('0' + ((byte / 10) % 10));   // Tens
  transmit_byte('0' + (byte % 10));         // Ones
}
 
// Prints a word (16-bits) out as its 5-digit ascii equivalent.
void print_word(uint16_t word)
{
  transmit_byte('0' + (word / 10000));       // Ten-thousands
  transmit_byte('0' + ((word / 1000) % 10)); //  Thousands
  transmit_byte('0' + ((word / 100) % 10));  //  Hundreds
  transmit_byte('0' + ((word / 10) % 10));   //  Tens
  transmit_byte('0' + (word % 10));          //  Ones
}
 
// Prints a byte out in 1s and 0s.
void print_binary_byte(uint8_t byte)
{
  uint8_t bit;
  for (bit = 7; bit < 255; bit--)
  {
    if (bit_is_set(byte, bit))
    {
      transmit_byte('1');
    }
    else
    {
      transmit_byte('0');
    }
  }
}
 
// Converts a nibble to a hexadecimal character
char nibble_to_hex_character(uint8_t nibble)
{
  if (nibble < 10)
  {
    return ('0' + nibble);
  }
  else
  {
    return ('A' + nibble - 10);
  }
}
 
// Prints a byte as its hexadecimal equivalent
void print_hex_byte(uint8_t byte)
{
  uint8_t nibble;
  nibble = (byte & 0b11110000) >> 4;
  transmit_byte(nibble_to_hex_character(nibble));
  nibble = byte & 0b00001111;
  transmit_byte(nibble_to_hex_character(nibble));
}
 
 // Gets a numerical 0-255 from the serial port, converts string to number.
uint8_t get_number(void)
{
  char hundreds = '0';
  char tens = '0';
  char ones = '0';
  char thisChar = '0';
  do
  {
    hundreds = tens;
    tens = ones;
    ones = thisChar;
    thisChar = receive_byte(); // get a new character
    transmit_byte(thisChar);   // echo
  }
  while (thisChar != '\r'); // until type return
 
  // TODO: Bracketise this further
  return (100 * (hundreds - '0') + 10 * (tens - '0') + ones - '0');
}
 
// TODO: Replace these with non-blocking waits
//Blocking transmit and receive functions.
static void transmit_byte(uint8_t data)
{
  // Wait for empty transmit buffer
  loop_until_bit_is_set(UCSR0A, UDRE0);
  // Send Data
  UDR0 = data;
}
 
static uint8_t receive_byte(void)
{
  // Wait for incoming data
  loop_until_bit_is_set(UCSR0A, RXC0);
  //return register value
  return UDR0;
}
 
 
/*** end of file ***/