#include "stm32f4xx.h"
#include "LCD2x16.c"

char *OutString;        // string must be terminated by '\0'

void main(void) {

  // GPIO clock enable, digital pin definitions
  RCC->AHB1ENR  |= 0x00000001;  // Enable clock for GPIOA
  RCC->AHB1ENR  |= 0x00000010;  // Enable clock for GPIOE
  GPIOE->MODER  |= 0x00010000;  // output pin PE08: time mark
  GPIOE->MODER  |= 0x00040000;  // output pin PE09: toggle
  GPIOA->MODER  |= 0x00001000;  // output pin PA06: LED D390
  GPIOA->MODER  |= 0x00004000;  // output pin PA06: LED D391
  GPIOC->MODER  |= 0x00900000;  // PC10, PC11 => AF mode
  GPIOC->AFR[0] |= 0x00000010;  // select AF1 (TIM2) for PA01 -> TIM2_CH2
  
  //UART4 initialization
  RCC->APB1ENR  |= 0x00080000;  // Enable clock for UART4
  RCC->AHB1ENR  |= 0x00000004;  // Enable clock for GPIOC
  GPIOC->MODER  |= 0x00a00000;  // PC10, PC11 => AF mode
  GPIOC->AFR[1] |= 0x00008800;  // select AF8 (UART4,5,6) for PA10, PA11 
  UART4->BRR     = 0x1120;      // 9600 baud
  //UART4->BRR     = 0x0890;      // 19200 baud
  //UART4->BRR     = 0x0450;      // 38400 baud
  //UART4->BRR     = 0x02e0;      // 57600 baud
  //UART4->BRR     = 0x016d;      // 115200 baud
  UART4->CR1    |= 0x200c;      // Enable UART for TX, RX
  UART4->CR1    |= 0x0020;      // Enable RX interrupt
  
  // LCD init
  LCD_init();                   // Init LCD

  //NVIC init
  NVIC_EnableIRQ(UART4_IRQn);   // Enable IRQ for UART4 in NVIC

  // endless loop
  while (1) {
    if (GPIOE->IDR & 0x0001) GPIOA->ODR |=  0x0040;   // LED on
    else                     GPIOA->ODR &= ~0x0040;   // else LED off
    if (GPIOE->IDR & 0x0002) UART4->DR = 'a';   // send    
    for (int i = 0; i<100000; i++) {};          // waste time
  };
}

// IRQ function
// caution: placing breakpoints in IRQ corrupts the execution!  
// this happends due to the reading of the DR by the IAR and changes IRQ flags!
// I wasted sevaral hours to find this out. Do not step into the same trap.
void UART4_IRQHandler(void)     {  
  // TX IRQ part
  if (UART4->SR & 0x0080) {     // If TXE flag in SR is on then
    if (*OutString != '\0')     // if not end of string
      UART4->DR = *OutString++; // send next character and increment pointer
    else                        // else
      UART4->CR1 &= ~0x0080;    // disable TX interrupt
  };
  // RX IRQ part
  if (UART4->SR & 0x0020) {     // if RXNE flag in SR is on then
    int RXch = UART4->DR;       // save received character & clear flag
    LCD_uInt16(RXch, 0x05, 1);  // show ASCII on LCD
    if (RXch == 'a') GPIOA->ODR |=  0x0080;   // if 'a' => LED on
    if (RXch == 'b') GPIOA->ODR &= ~0x0080;   // if 'b' => LED off
    if (RXch >= 'A' && RXch <= 'Z') UART4->DR = RXch;   // echo character
    if (RXch == 'c') {                        // if 'c' => return string
      OutString = "ABCDEFGH";   // Init string & ptr
      UART4->CR1 |= 0x0080;     // Enable TX IRQ
      UART4->DR = *OutString++; // Send first character
    };
  };
}