/* p3_2.c:  Initialize and display "Hello" on the LCD using 8-bit data mode.
 *
 * Data pins use Port C; control pins use Port B.
 * Polling of the busy bit of the LCD status register is used for timing.
 *
 * The LCD controller is connected to the Nucleo-F446RE
 * board as follows:
 *
 * PC0-PC7 for LCD D0-D7, respectively.
 * PB5 for LCD R/S
 * PB6 for LCD R/W
 * PB7 for LCD EN
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0
 */

#include "stm32f0xx.h"

#define RS 0x20         /* PB5 mask for reg select */
#define RW 0x40         /* PB6 mask for read/write */
#define EN 0x80         /* PB7 mask for enable */

void delayMs(int n);
void LCD_command(unsigned char command);
void LCD_command_noPoll(unsigned char command);
void LCD_data(char data);
void LCD_init(void);
void LCD_ready(void);
void PORTS_init(void);

int main(void)
{
	/* initialize LCD controller */
	LCD_init();

	while (1) {
		/* Write "Hello" on LCD */
		LCD_data('H');
		LCD_data('e');
		LCD_data('l');
		LCD_data('l');
		LCD_data('o');
		delayMs(500);

		/* clear LCD display */
		LCD_command(1);
		delayMs(500);
	}
}

/* Initialize port pins then initialize LCD controller */
void LCD_init(void)
{
	PORTS_init();

	delayMs(30);                    /* initialization sequence */
	LCD_command_noPoll(0x30);       /* LCD does not respond to status poll yet */
	delayMs(10);
	LCD_command_noPoll(0x30);
	delayMs(1);
	LCD_command_noPoll(0x30);       /* busy flag cannot be polled before this */

	LCD_command(0x38);              /* set 8-bit data, 2-line, 5x7 font */
	LCD_command(0x06);              /* move cursor right after each char */
	LCD_command(0x01);              /* clear screen, move cursor to home */
	LCD_command(0x0F);              /* turn on display, cursor blinking */
}

void PORTS_init(void)
{
	/* enable GPIOB/C clock */
	RCC->AHBENR |= 0x00040000;
	RCC->AHBENR |= 0x00080000;

	/* PB5 for LCD R/S */
	/* PB6 for LCD R/W */
	/* PB7 for LCD EN */
	GPIOB->MODER &= ~0x0000FC00;    /* clear pin mode */
	GPIOB->MODER |=  0x00005400;    /* set pin output mode */
	GPIOB->BSRR = 0x00C00000;       /* turn off EN and R/W */

	/* PC0-PC7 for LCD D0-D7, respectively. */
	GPIOC->MODER &= ~0x0000FFFF;    /* clear pin mode */
	GPIOC->MODER |=  0x00005555;    /* set pin output mode */
}

/* This function waits until the LCD controller is ready to
 * accept a new command/data before returns.
 * It polls the busy bit of the status register of the LCD controller.
 * To read the status register, the data port of the
 * microcontroller has to change to an input port before reading
 * the LCD. The data port of the microcontroller is returned to
 * output port before the end of this function.
 */
void LCD_ready(void)
{
	char status;

	/* change to read configuration to poll the status register */
	GPIOC->MODER &= ~0x0000FFFF;    /* clear pin mode */
	GPIOB->BSRR = RS << 16;         /* RS = 0 for status register */
	GPIOB->BSRR = RW;               /* R/W = 1 for read */

	do {                            /* stay in the loop until it is not busy */
		GPIOB->BSRR = EN;       /* pulse E high */
		delayMs(0);
		status = GPIOC->IDR;    /* read status register */
		GPIOB->BSRR = EN << 16; /* clear E */
		delayMs(0);
	} while (status & 0x80);        /* check busy bit */

	/* return to default write configuration */
	GPIOB->BSRR = RW << 16;         /* R/W = 0, LCD input */
	GPIOC->MODER |=  0x00005555;    /* Port C as output */
}

void LCD_command(unsigned char command)
{
	LCD_ready();                    /* wait for LCD controller ready */
	GPIOB->BSRR = (RS | RW) << 16;  /* RS = 0, R/W = 0 */
	GPIOC->ODR = command;           /* put command on data bus */
	GPIOB->BSRR = EN;               /* pulse E high */
	delayMs(0);
	GPIOB->BSRR = EN << 16;         /* clear E */
}

/* This function is used at the beginning of the initialization
 * when the busy bit of the status register is not readable.
 */
void LCD_command_noPoll(unsigned char command)
{
	GPIOB->BSRR = (RS | RW) << 16;  /* RS = 0, R/W = 0 */
	GPIOC->ODR = command;           /* put command on data bus */
	GPIOB->BSRR = EN;               /* pulse E high */
	delayMs(0);
	GPIOB->BSRR = EN << 16;         /* clear E */
}

void LCD_data(char data)
{
	LCD_ready();            /* wait for LCD controller ready */
	GPIOB->BSRR = RS;       /* RS = 1 */
	GPIOB->BSRR = RW << 16; /* R/W = 0 */
	GPIOC->ODR = data;      /* put data on data bus */
	GPIOB->BSRR = EN;       /* pulse E high */
	delayMs(0);
	GPIOB->BSRR = EN << 16; /* clear E */
}
/* delay n milliseconds (8 MHz CPU clock) */
void delayMs(int n)
{
	int i;

	for (; n > 0; n--)
		for (i = 0; i < 1142; i++);
}