Welcome in the fascinating world of PSoCs!
There is no direct API, but you could use an ADC to measure it. Can you be a bit more specific what you want to do, what your problem is?
There are basically two methods:
- use a voltage divider for the supply voltage, and measure the result with ADC (using a internal reference). This is the direct way
- use the supply voltage as the reference for the ADC, and measure the internal voltage reference with it. This is indirect (and needs conversion), but doesn't any external components.
The ADC-configuration using 6 * VRef is explicitely mentioned for measuring the supply-voltage.
Oh, I did forget about that ADC mode. Sure, that would be the easiest version.
When you setup A/D also make sure you set
input buffer to "bypass buffer" in order to get a
CM range that includes the rail (Vdda).