What is your SOW ? SOW = statement of work. What kind of RPM are you trying to measure? Your best bet is to use the PSOC Creator software as it writes the programs for the components. Post your code so we can check it.
Welcome in the world of PSoCs, Matthias.
When in Creator there is on the left hand side a window with some vertical tabs. The "Datasheet" tab shows the PSoC family members, from which you learn that the core is an ARM Cortex M0.
A widely used method is to measure the time between pulses. When using a clock with 1MHz you can have a resolution of 1 µs. Use the capture input of the counter to read the timer value in an interrupt handler.
PS: Where in Germany are you located? I live near Bremen.