Arm architecture and programming 1 -- LED flashing (based on Baiwen arm architecture and programming tutorial video)

One 、 How to operate registers

1、 Access memory

Read the value of the register , modify , Write back .（ The operation is complicated ）

int * p;
int Val;
p = (0x40010C00 + 0x0C);
Val = *p;
Val |= (1<<3);
*p = Val;

2、 Access registers

Write directly to the register .（ It's easy to operate ）

int * p;
p = (0x40010C00 + 0x0C);
*p |= (1<<3);

Two 、 Who will call main function

After hardware reset , The first step of the program is to execute the reset processing program .

In the reset handler , First, execute SystemInit Initialization function , Users can write this function by themselves , No keil To encapsulate . And then call main function .

got it main Calling procedure of function , You can write the startup process of the system by yourself . because main The function is a C function , So you need stack space , So also specify the stack space .

The above figure shows the stack space set in the official startup file .

This is the startup code written by myself , After reset , Execute first __Vectors Vector table , register Reset_Handler function , Then execute the reset function , In the reset function , Declare external functions main, Then set the stack space , Finally jump to main Function to execute function .

Stack space can be found in the official manual or in keil Select the corresponding chip in and check .

3、 ... and 、 Experimental code

1、 Related registers

Turn on the clock register

Because it is a direct operation register , So there is no need to include a pile of header files . Directly operate the corresponding register .

The essence of turning on the peripheral clock is to turn on the corresponding peripheral bus APB1 and APB2 Clock enable register RCC_APB2、1ENR Correlation bit of .

If the system does not configure the clock , The default system clock source after power on is HSI,8MHz.

Pin configuration register

GPIO There are two mode configuration registers of the pin , One is CRL、CRH Control a group GPIO The lower eight and the higher eight . such as GPIOB_CRL It's pins 0-7 Mode configuration ;GPIOB_CRH yes 8-15 Mode configuration of pins .

GPIOB_ODR It's a 32 Bit register , low 16 Bit effective , Relevant location 1 Then the corresponding pin outputs high level .

2、 Specific code

1、 Define a pointer to a specific register

unsigned int * pAPB2En = ( unsigned int * )(0x40021000 + 0x18);
unsigned int * pGPIOCrl = ( unsigned int * )(0x40010C00 + 0);
unsigned int * pGPIOOdr = ( unsigned int * )(0x40010C00 + 0X0c);

2、 By configuring registers

*pAPB2En |= (1<<3);// Register No 3 Location 1, Can make GPIOB The clock 
*pGPIOCrl |= (1<<0);// Register No 0 Location 1, Set up GPIOB10MHz Open drain output 
*pGPIOOdr |= (1<<0);// Set register number 0 Location 1,GPIOB_PIN0 Output high level , The light goes out 

3、LED flashing

while(1)
	{	
		delay();// Time delay 
		*pGPIOOdr &= ~(1<<0);//GPIOB_PIN0 Output low level , Light on 
		delay();// Time delay 
		*pGPIOOdr |= (1<<0);//GPIOB_PIN0 Output high level , The light goes out 
	}