====== System Tick Timer ======

The STM32F429ZI offers a 24 bit system tick timer. It is a simple down counter. \\
The system tick timer counts down from the reload value to zero and generates an interrupt. \\

\\ {{systick_complete.svg}} \\ \\

===== Registers =====

==== CTRL - Control and status register ====

\\ {{systick_reg_ctrl.svg}} \\ \\

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|ENABLE|0|Systick timer disabled (reset state)|
|:::|1|Systick timer enabled|
|TICKINT|0|Systick interrupt disabled (reset state)|
|:::|1|Systick interrupt enabled|
|CLKSRC|0|Systick clock => f<sub>HCLK</sub> / 8 (reset state)|
|:::|1|Systick clock => f<sub>HCLK</sub>|

==== LOAD - Reload value register ====

\\ {{systick_reg_load.svg}} \\ \\

* Reload value of SysTick timer.

==== VAL - Current value register ====

\\ {{systick_reg_val.svg}} \\ \\

* Current value of SysTick timer.

===== Programming Example =====

<code c>
#include "reg_stm32f4xx.h"

STK->CTRL = (0x3 << 1u);             /* Set clock and interrupt. */
STK->LOAD = 84000u;                  /* Set reload value: 84 MHz / 84000 -> 1 ms. */
STK->CTRL |= (0x1 << 0u);            /* Enable timer. */

void SysTick_Handler(void)
{
    /* Handler for SysTick interrupt. */
}
</code>
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