STM32 learning notes - using SysTick timer for delay-EEWORLD

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School has started, and I can no longer play with the board all day like I did during the holidays! Fortunately, the number of classes this semester is not too few, but not too many either, with more than a dozen classes per week. In the remaining time, apart from student work and other miscellaneous things, I can still read tutorials and play with the board from time to time! I find that the "STM32 Novice Learning Manual - Long-winded Edition" is a really good introductory tutorial, simple and easy to understand. Other official documents such as the "Firmware Library Manual" are even more indispensable, but it's a pity that it's really troublesome to find manuals on the ST company's website!

I have been looking at documents about SysTick these days, but since the 3.5 version of the firmware library has removed the driver functions related to SysTick compared to the 2.0 version, users must call the functions in CMSIS to use SysTick, and most of the examples on the Internet (including the "Rookie Learning Manual") use the 2.0 library, so I encountered many problems in learning, and there were always problems with program compilation. Generally, the error is "Cannot find the function related to SysTick, the function is undefined". Therefore, I searched a lot of literature to solve it.

The SysTick timer is bundled in the NVIC and is used to generate the SysTick exception (exception number: 15). It is mainly used in the operating system as a "tick interrupt" to maintain the rhythm of the operating system's "heartbeat". Of course, in addition to serving the operating system, the SysTick timer can also be used for other purposes: such as as an alarm, for measuring time, etc. It should be noted that when the processor is halted during debugging, the SysTick timer will also be suspended.

1.SysTick register:

register	illustrate	address
CTRL	SysTick Control and Status Register	0xE000E010
LOAD	Systick reload value register	0xE000E014
VAL	Systick Current Value Register	0xE000E018
CALIB	SysTick Calibration Value Register	0xE000E01C

l SysTick Control and Status Register (SysTick_CTRL)

STM32 learning notes - using SysTick timer for delay

illustrate:

CLKSOURCE bit: CM3 allows two clock sources to be selected for SysTick. The first is the core's "free running clock" FCLK. "Free" means that it does not come from the system clock HCLK, so FCLK continues to run when the system clock stops. The second is an external reference clock. However, when using an external clock, because it is sampled internally by FCLK, its period must be at least twice that of FCLK (sampling theorem). In many cases, chip manufacturers will ignore this external reference clock, so it is usually not available.

COUNTFLAG bit: When the SysTick timer counts from 1 to 0, it will set the COUNTFLAG bit; the following method can clear it:

Read the SysTick control and status register (STCSR);

Write any data to the SysTick Current Value Register (STCVR).

l SysTick reload value register (SysTick_LOAD)

STM32 learning notes - using SysTick timer for delay

illustrate:

When the counter counts down to 0, use the SysTick_LOAD register to specify the initial value loaded into the "Current Value Register". The initial value can be any value between 1 and 0x00FFFFFF. [page]

l Systick current value register (SysTick_VAL)

l SysTick calibration value register (SysTick_CALIB)

STM32 learning notes - using SysTick timer for delay

Schematic diagram of each register:

2. SysTick function

The STM32 firmware library after version 3.0 removes the SysTick driver in the standard peripheral library, so users must call the CMSIS-defined functions.

CMSIS only provides a SysTick setting function, which replaces all the functions of the original SysTick driver of STM32.

[cpp] view plain copy

SysTick_Config(uint32_t ticks);

This function sets the value of the auto-reload counter (LOAD), the priority of the SysTick IRQ, resets the value of the counter (VAL), starts counting and enables the SysTick IRQ interrupt. The SysTick clock uses the system clock by default.

In addition, you can use the SysTick_CLKSourceConfig function to change the clock source and use NVIC_SetPriority to set the interrupt priority (more on this later).

SysTick_CLKSourceConfig function

Function name	SysTick_CLKSourceConfig
Function prototype	SysTick_CLKSourceConfig(u32 SysTick_CLKSource)
Behavior Description	Configure the SysTick clock source
Input parameters	SysTick_CLKSource: Clock source of SysTick
Output parameters	none
return value	none
Prerequisites	none
Call functions	none

SysTick_CLKSource allowed values

SysTick_CLKSource	describe
SysTick_CLKSource_HCLK_Div8	The SysTick clock source is 1/8 of the AHB clock
SysTick_CLKSource_HCLK	The SysTick clock source is the AHB clock

[page]

example:

Select 1/8 of the AHB clock as the SysTick clock source

[cpp] view plain copy

SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK_Div8);

3. Routines

3.1 Program Code

This example code is modified from the example code for lighting up the LED lamp, using SysTick timing delay. Except for the delay, other codes remain unchanged, and the statements related to SysTick are commented.

[cpp] view plain copy

#include "stm32f10x.h"
void Delay(u32 nTime); //Declare delay function
void GPIO_Configuration(void);
int main(void)
{
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC,ENABLE);
GPIO_Configuration();
while(SysTick_Config(SystemCoreClock/1000)!=0); //Configure SysTick and load the initial value. The load value depends on the clock source frequency. A 72MHz clock source generates a 1ms interrupt and the load value needs to be (72000000/1000)
while(1)
{
GPIO_ResetBits(GPIOC,GPIO_Pin_7|GPIO_Pin_9);
GPIO_SetBits(GPIOC,GPIO_Pin_6|GPIO_Pin_8);
Delay(1000);
GPIO_ResetBits(GPIOC,GPIO_Pin_6|GPIO_Pin_8);
GPIO_SetBits(GPIOC,GPIO_Pin_7|GPIO_Pin_9);
Delay(1000);
GPIO_Write(GPIOC,0x0140);
Delay(1000);
GPIO_Write(GPIOC,0x0280);
Delay(1000);
}
}
void GPIO_Configuration(void)
{
GPIO_InitTypeDefGPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin=GPIO_Pin_6|GPIO_Pin_7|GPIO_Pin_8|GPIO_Pin_9;
GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode=GPIO_Mode_Out_PP;
GPIO_Init(GPIOC,&GPIO_InitStructure);
}
volatile u32 TimingDelay; //define global variables, which are declared in stm32f10x_it.c
void Delay(u32 nTime) //define delay function
{
TimingDelay=nTime; //Assign the delay number to the global variable
while(TimingDelay!=0);
}

Among them, in stm32f10x_it.c:

[cpp] view plain copy

extern volatile u32 TimingDelay; //declare global variables
void SysTick_Handler(void)
{
TimingDelay--;
}

3.2 Results

After compiling and burning into the development board, the LEDs will flash alternately with an accurate interval of 1 second.

references:

[1] Joseph Yiu, translated by Song Yan. "Cortex-M3 Authoritative Guide" [EB/OL]. http://ishare.iask.sina.com.cn/f/11378333.html?retcode=0, 2010-11-05/2012-09-09.

[2] ST. "Comparison of STM32 firmware library 2.0.3 and 3.0 versions (Chinese version)" [EB/OL]. http://ishare.iask.sina.com.cn/f/18297257.html?from=like, 2011-08-22/2012-09-09.

[3]Xxbing8.STM32_SysTick[EB/OL].http://hi.baidu.com/xxbing8/item/c99ea4f53f996ad042c36ab8 2012-06-14/2012-09-09.

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