HSE Predivider

[agrif]

I'm trying to use this crate with an STM32F103CBT6 board that uses a 16MHz HSE oscillator. In C-land, I use the HSE predivider to bump that down to 8MHz, and as far as I know, this is the only method available to have both a 72MHz SYSCLK as well as the required 48MHz USB clock.

In STM32CubeMX, the HSE predivider is here (and called "HSE Prediv"):

It doesn't look like this crate supports setting this predivider at all. In get_clocks(), the value for SYSCLK is calculated using the HSE, and possibly the PLL multiplier, but not any divider.

Is this reading correct? And can support for the HSE predivider be added?