STM32F3 Discovery reading values from sensor using I2C

Question

I need to read values from on-board LSM303DLHC (connected via I2C) sensor and send them through UART. UART part is working but PuTTy shows: "S▒▒" every restart... Can anyone tell me what's wrong? I know that I2C part is not perfect but it should return something, right?

PS. I don't want to use their library - I will learn more this way :)

#include "stm32f30x.h"
void SysTick_Handler(void);
void TimingDelay_Decrement(void);
void Delay(__IO uint32_t nTime);
static __IO uint32_t TimingDelay;
int b=0;
void UART_init (void);
void UART_SendChar (char data);
void USART_SendString (uint8_t * str);
int UART_read (void);
void i2c_conf();
void i2c_write_byte(uint8_t addr, uint8_t data);
uint8_t i2c_read_byte(uint8_t addr);
char read;
char data_from_i2c;
uint8_t CRA_REG_M = 0x00;
uint8_t MR_REG_M = 0x02;
uint8_t CRB_REG_M = 0x01;
uint8_t scldel;
uint8_t sdadel;
int main(void)
{
 SysTick_Config(SystemCoreClock / 1000); // Delay(1) = 1 ms with */1000
 UART_init();
 i2c_conf();
 /* ustaw zakres pomiarowy */
 i2c_write_byte(CRB_REG_M, 0x80);
 /* wlacz termometr i ustaw czestotliwosc odswiezania */
 i2c_write_byte(CRA_REG_M, 0x90);
 i2c_write_byte(MR_REG_M, 0x00);
 UART_SendChar('S'); 
 data_from_i2c = i2c_read_byte(0x03);
 UART_SendChar(data_from_i2c); 
 data_from_i2c = i2c_read_byte(0x04);
 UART_SendChar(data_from_i2c);
 while(1)
 {
// uint8_t String[]="Hello world!";
// USART_SendString (String);
// Delay(1000);
 read=UART_read();
 UART_SendChar(read);
 read=0;
 }
}
void SysTick_Handler(void)
{
 TimingDelay_Decrement();
}
void Delay(__IO uint32_t nTime)
{
 TimingDelay = nTime;
 while(TimingDelay != 0);
}
void TimingDelay_Decrement(void)
{
 if (TimingDelay != 0x00)
 { 
 TimingDelay--;
 }
}
void UART_init (void) {
 RCC -> AHBENR |= (1UL << 19); // Enable GPIOC clock
 GPIOC -> MODER |= (2 << 2*10) | (2 << 2*11); // PC10 PC11 as AF mode
 GPIOC -> AFR[1] |= (7 << 8); // PC10 as AF7 - USART3_TX
 GPIOC -> AFR[1] |= (7 << 12); // PC11 as AF7 - USART3_RX
 RCC->APB1ENR |= (1UL << 18); // Enable USART3 clock
 USART3 -> BRR = 3750; //Baudrate based on 24MHz clock 
 USART3 -> CR1 |= (USART_CR1_RE | USART_CR1_TE); 
 USART3 -> CR1 |= USART_CR1_UE;
}
void UART_SendChar (char data) {
 while( ( USART3 -> ISR & USART_ISR_TXE) == 0 ); 
 USART3 -> TDR = data;
}
void USART_SendString (uint8_t * str) {
 while(*str != 0) {
 UART_SendChar(*str); 
 str++;
 }
 UART_SendChar(10); 
 UART_SendChar(13); 
}
int UART_read (void)
{
 while ( (USART3->ISR & USART_ISR_RXNE) == 0); 
 return USART3-> RDR & USART_RDR_RDR;
}
void i2c_conf() {
 /* ustaw altenatywne funkcje GPIO */
 RCC -> AHBENR |= RCC_AHBENR_GPIOBEN;
 GPIOB -> OSPEEDR &= ~GPIO_OSPEEDER_OSPEEDR6 | ~GPIO_OSPEEDER_OSPEEDR7;
 GPIOB -> MODER |= GPIO_MODER_MODER6_1 | GPIO_MODER_MODER7_1;
 GPIOB -> OTYPER |= GPIO_OTYPER_OT_6 | GPIO_OTYPER_OT_7;
 GPIOB -> AFR[0] |= (4 << 24) | (4 << 28);
 /* zegar z APB1 - 72 MHz */
 //RCC->CFGR3 |= RCC_CFGR3_I2C1SW;
 RCC->APB1ENR |= RCC_APB1ENR_I2C1EN ;
 /* skonfiguruj I2C1 */
 I2C1->CR1 |= I2C_CR1_ANFOFF;
 scldel = 4;
 sdadel = 5;
 I2C1->TIMINGR = 0xF0001317 | ((scldel & 0x0F) << 20) | ((sdadel & 0x0F) << 16);
 I2C1->CR2 |= (0x1E << 1);
 I2C1->CR1 |= I2C_CR1_PE;
}
void i2c_write_byte(uint8_t addr, uint8_t data) {
 I2C1->CR2 &= ~(I2C_CR2_RD_WRN);
 I2C1->CR2 |= I2C_CR2_START | (2 << 16);
 while(I2C1->CR2 & I2C_CR2_START);
 I2C1->TXDR = addr;
 while (!(I2C1->ISR & I2C_ISR_TXE));
 I2C1->TXDR = data;
 while (!(I2C1->ISR & I2C_ISR_TXE));
 I2C1->CR2 |= I2C_CR2_STOP;
 while(I2C1->CR2 & I2C_CR2_STOP);
}
uint8_t i2c_read_byte(uint8_t addr) {
 uint8_t data = 0;
 I2C1->CR2 &= ~(I2C_CR2_RD_WRN);
 I2C1->CR2 &= ~(0xff << 16);
 I2C1->CR2 |= I2C_CR2_START | (1 << 16);
 while(I2C1->CR2 & I2C_CR2_START);
 I2C1->TXDR = addr;
 while (!(I2C1->ISR & I2C_ISR_TXE));
 I2C1->CR2 |= I2C_CR2_RD_WRN;
 I2C1->CR2 |= I2C_CR2_START | (1 << 16);
 while(I2C1->CR2 & I2C_CR2_START);
 while (!(I2C1->ISR & I2C_ISR_RXNE));
 data = I2C1->RXDR;
 I2C1->CR2 |= I2C_CR2_STOP;
 while(I2C1->CR2 & I2C_CR2_STOP);
 return data;
}

So the problem with UART is because I'm sending hex values which are shown as ASCII characters. So I'm receiving values which should be for example my X-axis acceleration data in two bits (High and Low) in two's complement. But how to convert that to decimal value and send it through UART?

• Ekci: So the problem with UART is because I'm sending hex values which are shown as ASCII characters. So I'm receiving values which should be for example my X-axis acceleration data in two bits (High and Low) in two's complement. But how to convert that to decimal value and send it through UART?

Answer 1

Problem solved. Here's corrected part of the code:

 i2c_write_byte(0x20, 0x37); //CTRL_REG1_A = 00110111b
 test = i2c_read_byte(0x28);
 test2 = i2c_read_byte(0x29);
 X = (int16_t)(test | test2 << 8);
 test = i2c_read_byte(0x2A);
 test2 = i2c_read_byte(0x2B);
 Y = (int16_t)(test | test2 << 8);
 test = i2c_read_byte(0x2C);
 test2 = i2c_read_byte(0x2D);
 Z = (int16_t)(test | test2 << 8);
 AccYangle = (float) atan2(Y, Z) * 180/M_PI;
 AccXangle = (float) atan2(-X, sqrt(Y*Y + Z*Z)) * 180/M_PI;
 sprintf(buffer, "X = %f", AccXangle);
 USART_SendString(buffer);
 sprintf(buffer, "Y = %f", AccYangle);
 USART_SendString(buffer);

And correct address of Accelerometer: I2C1->CR2 |= (0x19 << 1);