stm32/stm32l4 PWM: While attempting to output a 70 MHz square wave from the...

stm32/stm32l4 PWM: While attempting to output a 70 MHz square wave from the timer output of a STM32 clocked at 140 MHz (which works fine in baremetal C), I stumbled on what I believe to be an error in arch/arm/src/stm32/stm32_pwm.c.  Line 1304 we are told that

reload = timclk / info->frequency;

which I belive to be incorrect, it should be

reload = timclk / info->frequency - 1;

since starting to count from 0, if I want to output half of the TIM clock, I must count to 1 and not to 2.

Surely enough, the original code did output 140/3=47 MHz, while this correction does allow the output up to 70 MHz.

I am not sure this affects most users generating slow PWM (e.g. PX4) but for frequencies
close to the PCLK, indeed the difference becomes significant.