extern crate stm32f4;
use stm32f4::stm32f407;

// works
fn timer_val(peripherals: &stm32f407::Peripherals) -> u16 {
    let timer = &peripherals.TIM6;
    timer.cnt.read().cnt().bits()
}

// compile error "type error"
fn timer_val(peripherals: &stm32f407::Peripherals.TIM6) -> u16 {
    timer.cnt.read().cnt().bits()
}