I am going to use FTM capture mode for period measurement. Looking into the datasheet (VYBRIDRM.pdf), possible FTM clocks are: system clock, fixed frequency clock, external clock. I have not found a direct description of what the "system clock" is for FTM. I assumed that it is the System Core Clock for A5, that is, around 396MHz or so. But sample code showed that the real clock is only 66MHz (while A5 clocked at 396MHz). PDF references for other CPUs with FlexTimer explicitly tell that "FTM system closk is the bus clock, around 66MHz", but VYBRIDRM.pdf does not explain this (or I missed that). At the same time the table 9-10 (page 628) introduces "flex_root_clk" clock name, for which the maximum frequency is 85MHz. This flex_root_clk is found in the document just once, and no more references to it. It looks like FTM clock = Bus clock.
So my questions are:
- What is the maximum frequency for FTM clock of MVF61NN151CMK50?
- What the "system clock" for FTM is?
- Where it is documented for this chip?