STM32F103C8T6: I2C Master does not generate START bit

DPosv.1 · ‎2020-02-20

I am programming Blue Pill stm32f103c8t6 mcu, and I am having troubles implementing I2C driver for it. I have tried one I2C example from one site, then tried to implement it on my own by datasheet, yet it does not work - it does not generate START.

I know this I2C and I2C device work, because I have tried using STM32Duino software and the device with address 72 replied, but I have troubles reimplementing it on my own. I use CMSIS, no HAL and the minimal code is as follows:

void i2c_init() {
 
  I2C_InitTypeDef i2c_initstruct;
  I2C_StructInit(&i2c_initstruct);
 
  // Initialize I2C
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_I2C2, ENABLE);
  i2c_initstruct.I2C_ClockSpeed = 100e3;
  i2c_initstruct.I2C_Mode = I2C_Mode_I2C;
  i2c_initstruct.I2C_DutyCycle = I2C_DutyCycle_2;
  i2c_initstruct.I2C_OwnAddress1 = 0;
  i2c_initstruct.I2C_Ack = I2C_Ack_Disable;
  i2c_initstruct.I2C_AcknowledgedAddress = I2C_AcknowledgedAddress_7bit;
  I2C_Init(I2C2, &i2c_initstruct);
  I2C_Cmd(I2C2, ENABLE);
 
  // Initialize GPIO as open drain alternate function
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);
  GPIO_InitTypeDef GPIO_InitStruct;
  GPIO_InitStruct.GPIO_Pin = GPIO_Pin_10 | GPIO_Pin_11;
  GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_OD;
  GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
  GPIO_Init(GPIOB, &GPIO_InitStruct);
 
}
 
void i2c_start2(uint8_t addr_with_mode) {
nlio_print("(0");
 
  // Wait until no longer busy
  while((I2C2->SR2 & I2C_SR2_BUSY) != 0);
  // Send start bit
  I2C2->CR1 |= I2C_CR1_START;
 
  // Wait until no longer busy
  while((I2C2->SR2 & I2C_SR2_BUSY) != 0);
 
  //while((I2C2->SR2 & I2C_SR2_MSL) == 0);
 
nlio_print("(1");
  // Wait until START bit is actually sent
  while((I2C2->SR1 & I2C_SR1_SB) == 0);
 
nlio_print("(2");
  // Write address
  I2C2->DR = addr_with_mode;
 
nlio_print("(3");
  // Wait for ACK (address match)
  while((I2C2->SR1 & I2C_SR1_ADDR) == 0);
 
nlio_print("(4");
  // Read SR1 followerd by SR2 to clear (I2C->SR1 & ADDR)
  (void) I2C2->SR2;
}
 
void i2c_send(uint8_t byte) {
  // Wait until Data register is empty
  while((I2C2->SR1 & I2C_SR1_TXE) == 0);
 
  // Send byte
  I2C2->DR = byte;
}
 
void i2c_end() {
  // Wait until Data register is empty
  while((I2C2->SR1 & I2C_SR1_TXE) == 0);
 
  // Wait until Byte transfer finished
  while((I2C2->SR1 & I2C_SR1_BTF) == 0);
 
  // Send stop
  I2C2->CR1 |= I2C_CR1_STOP;
}
 
#define WRITE 0
 
void i2c_test() {
  i2c_init();
 
  nlio_print("Hello\r\n");
  i2c_start2((72 << 1) | WRITE);
  nlio_println("Chp1");
  i2c_send(0);
  nlio_println("Chp2");
  i2c_end();
  // i2c_write(72, 0);
 
  nlio_println("Chp4");
  uint8_t rec;
  i2c_read(72, &rec);
  nlio_println("Chp5");
 
  // uart_println("Wait busy");
  // i2c_wait_busy();
  // uart_println("Wait done");
 
  // info();
  while(1);
 
 
  // uart_println("Sending STOP");
  // i2c_read(72);
 
  // uart_println("DONE\n");
 
  // while(1) {
  //   info();
  // }
}
 
int main() {
  // ...
  nlio_print("NLIO\r\n");
  i2c_test();
  while(1);
}

and it hangs when waiting for START condition, so the output is as follows:

NLIO
Hello
(0(1

I have also soldered two pull-up 5k1 resistors connecting SDL and SCL to 3.3V, yet it still hangs.

I have no clue what I am doing wrong. Any help is appreciated.

waclawek.jan · ‎2020-02-20

Observe SDA/SCL pins, using oscilloscope/logic analyzer.

Read out the I2C registers and check/compare to working example.

JW

DPosv.1 · ‎2020-02-20

Thanks for your answer. It ***** that I currently I don't have an oscilloscope, even though I have recently ordered low speed one. I will try the register reading at least, and if it won't help I guess I will have to wait until it arrives.

DPosv.1 · ‎2020-02-20

Thanks for your answer. I currently I don't have an oscilloscope, even though I have recently ordered low speed one. I will try the register reading at least, and if it won't help I guess I will have to wait until it arrives.

berendi · ‎2020-02-20

Try initializing GPIO first, and I2C afterwards. Print the control and status registers at every step.

DPosv.1 · ‎2020-02-20

Tried initializing GPIO first, didn't help. Looking at the registers, even though I don't really know what exactly I should look for.

DPosv.1 · ‎2020-02-20

The content of the registers immediately after printing "(0" is following

and immediately after printing "(1" the registers change and SR2 indicates I2C is busy:

and since then nothing changes, the registers remaing with those values.

TEMAN.1 · ‎2020-03-16

Did you check "anolog function" init?

AFIO->MAPR &=~ 0x00000002; // GPIOB 6 and 7 AF

if you wanna use 8.and 9. pins, then

AFIO->MAPR =| 0x00000002; // GPIOB 8 VE 9 AF

and if i am not wrong, your pins cant be 10 and 11