stm32f407滴答定时器 ms

### STM32F407 SysTick Timer Millisecond Delay Implementation

In the context of configuring a system with an emphasis on debugging tools and optimization settings, it is important to understand how to implement precise delays using the SysTick timer within the STM32F407 microcontroller. The configuration starts by setting up the main clock frequency at 128 MHz[^1]. This setup ensures that timing-sensitive operations can be accurately controlled.

The SysTick timer provides a simple way to create millisecond-level delays which are often necessary for various applications such as LED blinking or periodic tasks execution. Below demonstrates initializing the SysTick timer for generating accurate millisecond delays:

#### Initializing SysTick Timer

To initialize the SysTick timer properly, one must configure its reload value based on the core clock speed (HCLK), ensuring each tick represents exactly 1 ms. Given HCLK runs at 128 MHz after initialization, calculations need adjustment accordingly when determining appropriate values for `SysTick_Config`.

#include "stm32f4xx.h"

void systick_init(void){
    if (SysTick_Config(SystemCoreClock / 1000)){ // Assuming SystemCoreClock equals HCLK set to 128MHz.
        while (1);                               // If configuration fails: stay here forever.
    }
}

This function configures the SysTick timer so that interrupts occur every millisecond. It uses `SystemCoreClock`, defined elsewhere in startup files typically provided by STMicroelectronics HAL libraries or CMSIS headers, representing the current CPU clock rate post-initialization processes including PLL configurations mentioned earlier.

#### Implementing Delays Using SysTick Handler

Once configured correctly, implementing delays becomes straightforward through handling interrupt requests generated periodically from this hardware peripheral. Here’s how to achieve non-blocking delays without halting program flow entirely during wait periods:

volatile uint32_t msTicks = 0;

void SysTick_Handler(void){
    msTicks++;
}

void delay_ms(uint32_t nms){
    uint32_t cur_ticks = msTicks;
    uint32_t target_tick = cur_ticks + nms;

    while(msTicks < target_tick);
}

Here, `delay_ms` waits until enough ticks have passed since calling time equating desired milliseconds count. Interrupt service routine increments global variable `msTicks` upon each occurrence thus allowing tracking elapsed real-time easily outside ISRs too.

--related questions--

1. How does changing the code optimization level affect performance?
2. What alternatives exist besides ITM for tracing debug information over UART interfaces?
3. Can you explain more about configuring other peripherals like ADC alongside SysTick timers?
4. Is there any impact of different power modes on SysTick functionality?