STM32F767 ZI, Trouble understanding how HAL_I2C_MASTER transmit works. Trying to send 32 bit adc data over I2C

[HSyed.1]

So I am trying to send an ADC value that I receiving on the board over I2C to another device.

I have adc_Value as a 32 bit one since the ADC read function on HAL is 32 bits.

I want to send this over i2c.

Currently I have this.

 HAL_ADC_Start(&hadc1); // starts the adc

   HAL_ADC_PollForConversion(&hadc1, 1); //

   // HAL_Delay(2000);

   ADC_Value = HAL_ADC_GetValue(&hadc1);

    HAL_I2C_Master_Transmit(&hi2c4, slave_addr, (uint8_t*)ADC_Value, 4, 50); // issue with (uint8_t *)

so I was confused about the casting here, I know that they want to send 8 bits but I was wondering since you can select the size as 4 bytes if it would send all 4.

I was thinking then of splitting my adc value into 4 bytes then just sending them one at a time.

Am i able to just send 32bits over I2c?

[TDK]

> HAL_I2C_Master_Transmit(&hi2c4, slave_addr, (uint8_t*)ADC_Value, 4, 50); // issue with (uint8_t *)

Almost. Assuming ADC_Value is a uint32_t, you want to pass the address of it, not its actual value.

HAL_I2C_Master_Transmit(&hi2c4, slave_addr, (uint8_t*) &ADC_Value, 4, 50);

The casting is needed because the parameter expects a pointer to uint8_t and not uint32_t, and pointers cannot be implicitly converted between those two.

Edit: Also, the ADC value is probably packed into the lower 2 bytes (or possibly only one byte), and data is stored in little endian format, so only sending the first 1 or 2 bytes instead of all 4 will suffice. So just make ADC_Value a uint16_t.

[HSyed.1]

Oh ok, yeah most of that makes sense, I chose ADC_Value to be 32 because HAL_read adc returned a 32 bit. So the 4 in the parameters will send 4 bytes from the pointers, so in my cause I will only need to do 2 after i change adc_value to 16 bit. So then I just need to make sure that my receiving program will read 2 bytes then. Also if I am not wrong I belive ( uint8_t * ) takes care of the pointer and another alternative is (uint8_t) &.( this is something I need to double check).

[TDK]

> Also if I am not wrong I belive ( uint8_t * ) takes care of the pointer and another alternative is (uint8_t) &.( this is something I need to double check).

Neither of those will do what you want. The former will compile without errors, but that doesn't mean it'll work.