src/hardware/usart.c File Reference

Implements a driver for USART0, which is connected to the host. More...

#include "usart.h"
#include "yarf.h"
#include "fastio.h"
#include <stdint.h>
#include <stdio.h>
#include <math.h>
#include <avr/interrupt.h>
#include <util/setbaud.h>

Go to the source code of this file.

Defines
#define	BAUD   HOST_BAUD_RATE
	The baud rate, which must be defined before loading the <util/setbaud.h> helper macros.
#define	ERROR_CHARACTER   ((char)0xFE)
	A character which can be inserted into the input buffer to signal the occurrence of an error while receiving a character.
Functions
static uint8_t	buf_index_next (uint8_t index)
	Returns the successor index of the given index in the input buffer.
static uint8_t	buf_index_prev (uint8_t index)
	Returns the predecessor index of the given index in the input buffer.
static bool	buf_full (void)
	Returns whether the input buffer is full.
static bool	buf_empty (void)
	Returns whether the input buffer is empty.
static void	usart0_init (void)
	Initializes the USART0 hardware.
static int	usart0_putchar (char c, FILE *stream)
	Sends a character to the USART hardware buffer and waits until it has been transmitted.
static int	usart0_getchar (FILE *stream)
	Returns the first unread character from the USART.
static void	read_character (void)
	Reads a character from the USART hardware buffer and appends it to the input buffer.
	ISR (USART0_RX_vect, ISR_BLOCK)
	Interrupt service routine which is called whenever a new character has arrived in the USART hardware buffer.
void	usart_init (void)
	Initializes the usart component.
void	usart0_try_read_character (void)
	If a character is waiting in the USART hardware buffer, this function reads that character and places it into the input buffer.
Variables
static volatile char	rx_buffer [USART0_RECEIVE_BUFFER_SIZE]
	Array for buffering incoming characters.
static volatile uint8_t	rxbuf_head
	The index of the head of the input buffer.
static volatile uint8_t	rxbuf_tail
	The index of the tail of the input buffer.
FILE	usart0_stream = FDEV_SETUP_STREAM(usart0_putchar, usart0_getchar, _FDEV_SETUP_RW)
	Stream which can be used to read from and write to the USART.

---

Detailed Description

Implements a driver for USART0, which is connected to the host.

Author:

Pieter Agten (pieter.agten@gmail.com)

Date:

18 sep 2011

Definition in file usart.c.

---

Define Documentation

#define BAUD   HOST_BAUD_RATE

The baud rate, which must be defined before loading the <util/setbaud.h> helper macros.

See also:

config.h

Definition at line 46 of file usart.c.

#define ERROR_CHARACTER   ((char)0xFE)

A character which can be inserted into the input buffer to signal the occurrence of an error while receiving a character.

This can be any non-ASCII character.

Definition at line 54 of file usart.c.

---

Function Documentation

static bool buf_empty

(

void

)

[inline, static]

Returns whether the input buffer is empty.

Returns:

whether the input buffer is empty

Definition at line 122 of file usart.c.

static bool buf_full

(

void

)

[inline, static]

Returns whether the input buffer is full.

Returns:

whether the input buffer is full

Definition at line 111 of file usart.c.

static uint8_t buf_index_next

(

uint8_t

index

)

[inline, static]

Returns the successor index of the given index in the input buffer.

Parameters:

index

the index of which to return the successor

Returns:

the successor index of the given index in the input buffer

Definition at line 80 of file usart.c.

static uint8_t buf_index_prev

(

uint8_t

index

)

[inline, static]

Returns the predecessor index of the given index in the input buffer.

Parameters:

index

the index of which to return the predecessor

Returns:

the predecessor index of the given index in the input buffer

Definition at line 96 of file usart.c.

static void read_character

(

void

)

[inline, static]

Reads a character from the USART hardware buffer and appends it to the input buffer.

If the hardware buffer is full or an error occurred while reading or receiving the character, a special ERROR_CHARACTER is written to the input buffer at the position of the last character previously received.

Definition at line 223 of file usart.c.

static int usart0_getchar

(

FILE *

stream

)

[static]

Returns the first unread character from the USART.

Parameters:

stream

a reference to the stream to which the character will be written

Returns:

the first unread character from the USART or _FDEV_ERR if there was a problem reading the character

The actual reception is line buffered, and one character is returned from the input buffer at each invokation of this function. If the buffer is empty, this function will wait for a new character to arrive. If there was a problem reading the character to be returned, the function returns the _FDEV_ERR error character.

Definition at line 198 of file usart.c.

static int usart0_putchar	(	char	c,
		FILE *	stream
	)		[static]

Sends a character to the USART hardware buffer and waits until it has been transmitted.

Parameters:

c	the character to transmit
stream	a reference to the underlying stream object from which the character is sent

Returns:

0 on success and a nonzero value if the character could not be transmitted

Definition at line 166 of file usart.c.

void usart0_try_read_character

(

void

)

If a character is waiting in the USART hardware buffer, this function reads that character and places it into the input buffer.

This function can be called from within long interrupt service routines that have higher priority than the USART0_RX interrupt, in order to prevent the hardware buffer from overrunning.

Definition at line 262 of file usart.c.

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Variable Documentation

volatile char rx_buffer[USART0_RECEIVE_BUFFER_SIZE] [static]

Array for buffering incoming characters.

This array is used as a circular buffer.

Definition at line 61 of file usart.c.

volatile uint8_t rxbuf_head [static]

The index of the head of the input buffer.

This is where new characters will be inserted.

Definition at line 66 of file usart.c.

volatile uint8_t rxbuf_tail [static]

The index of the tail of the input buffer.

This is where the next character will be fetched from, when reading from the input.

Definition at line 71 of file usart.c.