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

char SPItransaction (int AandD)    {    // about 7us
#define MOSI 0x8000
#define MISO 0x4000
#define SCK  0x2000
#define SEL  0x1000
int Ret = 0;
  GPIOB->ODR &= ~SEL;                   // SPI select
  for (char k = 0; k<16; k++)    {      // for 16 bits
    if (AandD & 0x8000) GPIOB->ODR |=  MOSI;      // send address & data
    else                GPIOB->ODR &= ~MOSI;      // 
    AandD <<= 1;                        // next bit of address & data
    GPIOB->ODR &= ~SCK;                 // SCL lo
    for (int i = 0; i<10; i++) {};      // waste 150ns
    Ret <<= 1;                          // shift bits read right
    GPIOB->ODR |=  SCK;                 // SCL hi
    if (GPIOB->IDR & MISO) Ret++;       // read bit and add to string
  };
  GPIOB->ODR |=  SEL;                   // SPI done
  return ((char)(Ret & 0xff));          // return result
}

void SPIwrite(int Adr, int Data)   {
  SPItransaction(((Adr & 0x3f) << 8) + Data);   // prepare 16 bits
}

char SPIread(int Adr)               {
  char Ret = SPItransaction(((Adr & 0x3f) << 8) + 0x8000); // 16 bits
  return (Ret);                                 // return result
}

void main ()  {

  // ports init: 15-MOSI, 14-MISO, 13-SCK, 12-SEL
  RCC->AHB1ENR  |=  0x00000002; // Enable clock for GPIOB
  GPIOB->MODER  &= ~0x80000000; // PB 15 => input pin, no AF!
  GPIOB->MODER  |=  0x45000000; // PB 15,13,12 => outputs
  GPIOB->ODR    |=  0xc000;     // SEL & SCK -> hi
  
  // Init accelerometer chip
  SPIwrite(0x20, 0xc7);         // CR1: power-up, all axes
  SPIwrite(0x21, 0x40);         // CR2: Block data update & 12 bit mode
  SPIwrite(0x22, 0x00);         // CR3: no filtering
  
  // Init LCD & prepare display
  LCD_init();                           // Init LCD
  LCD_string("x=       mg", 0x00);      // prepare 1st row
  LCD_string("y=       mg", 0x40);      // prepare 2nd row

  // endless loop
  while (1) {
    short retX = SPIread(0x28) + (SPIread(0x29) << 8);  // read x axix, both bytes
    LCD_sInt16(retX, 0x02, 1);                          // display result
    short retY = SPIread(0x2a) + (SPIread(0x2b) << 8);  // read y axix, both bytes
    LCD_sInt16(retY, 0x42, 1);                          // display result
    for (int i=0; i<1000000; i++)       {};             // waste time, ~30ms
  };
}