/*
 * Initialize LCD controller and flash "HELLO" on LCD.
 *
 * The LCD controller of EduBase board is connected to
 * the Nucleo board in parallel.
 *
 * The signals for LCD:
 * D4 - PB12
 * D5 - PB13
 * D6 - PB14
 * D7 - PB15
 * RS - PA11
 * EN - PA12
 * For simplicity, all delay below 1 ms uses 1 ms.
 */

#include "stm32f4xx.h"

#define RS 1        /* reg select */

void delayMs(int n);
void delayUs(int n);
void LCD_nibble_write(char data, unsigned char control);
void LCD_command(unsigned char command);
void LCD_data(char data);
void LCD_init(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(1000);

        /* clear LCD display */
        LCD_command(1);
        delayMs(1000);
    }
}

/* initialize the ports then the LCD controller */
void LCD_init(void) {
    PORTS_init();	/* initialize the ports that connect to the LCD */

    /* LCD controller reset sequence */
    delayMs(20);
    LCD_nibble_write(0x30, 0);
    delayMs(5);
    LCD_nibble_write(0x30, 0);
    delayMs(1);
    LCD_nibble_write(0x30, 0);
    delayMs(1);
    LCD_nibble_write(0x20, 0);  /* use 4-bit data mode */
    delayMs(1);
    LCD_command(0x28);          /* set 4-bit data, 2-line, 5x7 font */
    LCD_command(0x06);          /* move cursor right */
    LCD_command(0x01);          /* clear screen, move cursor to home */
    LCD_command(0x0F);          /* turn on display, cursor blinking */
}

void PORTS_init(void) {
    RCC->AHB1ENR |=  1;             /* enable GPIOA clock */
    RCC->AHB1ENR |=  2;             /* enable GPIOB clock */

    GPIOB->MODER &= ~0xFF000000;    /* clear pin mode */
    GPIOB->MODER |=  0x55000000;    /* set PB15-12 to output mode */

    GPIOA->MODER &= ~0x00C00000;    /* clear pin mode */
    GPIOA->MODER |=  0x00400000;    /* set PA11 to output mode */

    GPIOA->MODER &= ~0x03000000;    /* clear pin mode */
    GPIOA->MODER |=  0x01000000;    /* set PA12 to output mode */
}

void LCD_nibble_write(char data, unsigned char control) {
    /* populate data bits */
    GPIOB->BSRR = 0xF0000000;   // clear D7-4
    GPIOB->BSRR = data << 8;    // set D7-4

    /* set R/S bit */
    if (control & RS)
        GPIOA->BSRR = 0x0800;
    else
        GPIOA->BSRR = 0x08000000;

    /* pulse E */
    delayMs(0);
    GPIOA->BSRR = 0x00001000;
    delayMs(0);
    GPIOA->BSRR = 0x10000000;
}

void LCD_command(unsigned char command) {
    LCD_nibble_write(command & 0xF0, 0);    /* upper nibble first */
    LCD_nibble_write(command << 4, 0);      /* then lower nibble */

    if (command < 4)
        delayMs(2);         /* command 1 and 2 needs up to 1.64ms */
    else
        delayMs(1);         /* all others 40 us */
}

void LCD_data(char data) {
    LCD_nibble_write(data & 0xF0, RS);      /* upper nibble first */
    LCD_nibble_write(data << 4, RS);        /* then lower nibble */

    delayMs(1);
}

/* 16 MHz SYSCLK */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 3195; i++) ;
}