stm_systick.ctrl = ((1 << STM_SYSTICK_CTRL_ENABLE) |
(1 << STM_SYSTICK_CTRL_TICKINT) |
(STM_SYSTICK_CTRL_CLKSOURCE_HCLK_8 << STM_SYSTICK_CTRL_CLKSOURCE));
stm_systick.ctrl = ((1 << STM_SYSTICK_CTRL_ENABLE) |
(1 << STM_SYSTICK_CTRL_TICKINT) |
(STM_SYSTICK_CTRL_CLKSOURCE_HCLK_8 << STM_SYSTICK_CTRL_CLKSOURCE));