example1.c

/**
 * An example of some bad C code.
 *
 * Copyright (c) Jonathan 'theJPster' Pallant 2019
 *
 * This example is under the Blue Oak Model Licence: https://blueoakcouncil.org/license/1.0.0
 */

// ===========================================================================
// System Includes
// ===========================================================================

#include <stdbool.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

// ===========================================================================
// Macros
// ===========================================================================

/**
 * How big our buffer is.
 */
#define NUM_CHARS 16

/**
 * Some imaginary hardware UART register.
 */
#define UART_FIFO ((uint32_t*) 0x40004010U)

// ===========================================================================
// External Function Declarations
// ===========================================================================

/**
 * Normally this would be in a header file.
 */
extern void uart_write(const char* fmt, ...);

// ===========================================================================
// Private Variable Definitions
// ===========================================================================

/**
 * The buffer we store our UART characters in.
 */
static char character_buffer[NUM_CHARS];
/**
 * The number of characters we have in our UART buffer.
 */
static size_t num_chars_in_buffer;

// ===========================================================================
// Private Function Declarations
// ===========================================================================

static bool has_characters(void);
static char get_character(void);

// ===========================================================================
// Public Functions
// ===========================================================================

/**
 * Called when our startup code has finished.
 *
 * Never exits. Simply prints out the characters received on the UART.
 */
int main(void) {
	char *c = malloc(16);
	sprintf(c, "%s%s%s%s%s", "test", "test", "test", "test", "test");
	uart_write("%s", c);
	while(true) {
		if (has_characters()) {
			char x = get_character();
			uart_write("I got character %u (which is '%c')!", x);
		}
	}
}

/**
 * Called whenever a character is available in the hardware UART FIFO. Stuffs
 * the character into our buffer so the main loop can read it.
 */
void UART_Interrupt(void) {
	if (num_chars_in_buffer < NUM_CHARS) {
		character_buffer[num_chars_in_buffer] = *UART_FIFO;
		num_chars_in_buffer++;
	}
}

// ===========================================================================
// Private Functions
// ===========================================================================

/**
 * Return true if there is something in the buffer, false otherwise.
 */
static bool has_characters(void) {
	if (num_chars_in_buffer > 0) {
		return true;
	} else {
		return false;
	}
}

/**
 * Get a character from the buffer. Returns 'null' character if buffer is empty.
 */
static char get_character(void) {
	char c = '\0';
	if (num_chars_in_buffer > 0) {
		c = character_buffer[0];
		memmove(
			&character_buffer[1],
			&character_buffer[0],
			num_chars_in_buffer - 1
		);
	}
	return c;
}

// ===========================================================================
// End of File
// ===========================================================================