So I got in touch with ST and they said there was a problem that was fixed in v.1.7.1 of the HAL Libraries where if an interrupt occured during an I2C read it would cause the I2C receive register to get out of sync by 1 byte. I was using v.1.7.0 and they are currently on v. 1.7.3. I tried doing a "dummy read" as others in this thread have suggested and that did not work 100% (though it seemed to help for a while). ST recommended that I update my HAL Library files to v.1.7.3 and reprogram my targets. Here is a detailed explanation of the problem I received in e-mail.
The issue was relevant to how the RXNE and STOP flag were managed inside the static function I2C_WaitOnRXNEFlagUntilTimeout, which is used in polling mode.
Basically the bug could happen if the function would be interrupted in a specific point by an interrupt, like the systick. In the following the details:
static HAL_StatusTypeDef I2C_WaitOnRXNEFlagUntilTimeout
(I2C_HandleTypeDef *hi2c, uint32_t Timeout, uint32_t Tickstart)
while (__HAL_I2C_GET_FLAG(hi2c, I2C_FLAG_RXNE) == RESET)
{
/* Check if a NACK is detected */
if (I2C_IsAcknowledgeFailed(hi2c, Timeout, Tickstart) != HAL_OK)
{
return HAL_ERROR;
}
// At this moment the last byte is being received but not
completely received (let's say few bits received)
// Systick gets fired and loads the CPU for few microseconds
// I2C hardware receives the last byte in RXDR and generates the
NAK and STOP condition as it was set to auto end in I2C_TransferConfig
()
// Systick finishes the processing
// CPU gets back to I2C_WaitOnRXNEFlagUntilTimeout() and the first
thing to check the STOP flag which is already set
// The HAL driver returns a timeout and the last byte is not
copied in the user buffer but the RXDR register does have that data
/* Check if a STOPF is detected */
if (__HAL_I2C_GET_FLAG(hi2c, I2C_FLAG_STOPF) == SET)
{
/* Clear STOP Flag */
__HAL_I2C_CLEAR_FLAG(hi2c, I2C_FLAG_STOPF);
/* Clear Configuration Register 2 */
I2C_RESET_CR2(hi2c);
hi2c->ErrorCode = HAL_I2C_ERROR_NONE;
hi2c->State = HAL_I2C_STATE_READY;
hi2c->Mode = HAL_I2C_MODE_NONE;
/* Process Unlocked */
__HAL_UNLOCK(hi2c);
return HAL_ERROR;
}
