Why that complicated UART baudrate formula for STM32F1

[Uwe Bonnes]

In RM0008 cha 27.3.4 talks of " Fractional baud rate generation" and goes at length with examples of those fractional number. If the "fractional" stuff is broken down to integers, it boils down that simply

baud = f(clk) / BRR.

Or, as libopencm3 writes: "marketing babble to sound awesome: