Why DAC output nothing in software trigger?
I am use STM32L431RCT6,and my CubeMX config is this:

And my code is:
```
uint32_t data = 128;
ret = HAL_DAC_SetValue(&hdac1, DAC_CHANNEL_1, DAC_ALIGN_8B_R, data);
if(ret) {
HAL_Delay(10);
}
ret = HAL_DAC_Start(&hdac1, DAC_CHANNEL_1);
if(ret) {
HAL_Delay(10);
}
```
And if my Trigger method use None, measure is OK(middle with VCC).
I do not know why.
