stm32 timebase, SYS.

'When FreeRTOS is used, it is strongly recommended to use a HAL timebase source other than the systick.'
-- The HAL timebase source can be changed from the Pinout tab under SYS

到 Pinout tab 的 SYS，果然有 Timebase Source 可以選：

• SysTick
• TIM2
• TIM3
• TIM6
• TIM7
• TIM21
• TIM22