Arm architecture and programming 3 -- key control LED (based on Baiwen arm architecture and programming tutorial video)

1、 Assembly implementation LED flashing

According to the previous compilation knowledge , You can know how to use assembly operation register and realize function call and parameter transfer . The following is the assembly code implementation written by myself LED flashing .

delay_A		; No parameter , No return value delay function 
	ldr		r1,=0x30d40	; Function local variable 200000
loop_delay_A
	subs	r1,r1,#1	; Local variable minus 1, The calculation results affect PSR
	bne		loop_delay_A	;r1 != 0, Continue to cycle 
	bx		lr	;r1 = 0, The loop ends , return while loop 

delay_B		; With parameters , Delay function with return value , Using stack operations 
	push	{r0,lr}	; Put parameters 5000 And return address pushed onto the stack 
	nop
loop_delay_B
	ldr		r1,[sp,#0]	; Read the data in the stack , That is to say 200000
	subs	r2,r1,#1	; Local variable minus 1 Save in R2, The calculation results affect PSR
	str		r2,[sp,#0]	; Save the changed variables on the stack 
	bne		loop_delay_B	;r1 != 0, Continue to cycle 
	mov		r0,#0xff	; The return value is stored in r0
	pop		{r3,pc}	; Out of the stack , hold lr The address in is assigned to PC, The program jumps to the return address to continue execution 

main 
	; Can make GPIO The clock 
	ldr		r1,=0x40021000
	add		r1,r1,#0x18	; Set the real address = Base address + offset 
	ldr		r2,[r1]	; Read register 
	orr		r2,r2,#8	; Bit operation , Third place 1
	str		r2,[r1]	; Write register 
	; Set up GPIO The output mode 
	ldr		r1,=0x40010C00
	add		r1,r1,#0
	ldr		r2,[r1]
	orr		r2,r2,#1
	str		r2,[r1]
	; Set up GPIO Output high level , The light goes out 
	ldr		r1,=0x40010C00
	add		r1,r1,#0X0c
	ldr		r2,[r1]
	orr		r2,r2,#1	;bit0 = 1
	str		r2,[r1]
	;while loop 
loop
	; Call delay function delay_A-- No parameters 
	bl		delay_A	; No parameters , No use R0 Save parameters , Direct jump 
	;GPIO Output low level , Light on 
	ldr		r1,=0x40010C00
	add		r1,r1,#0X0c
	ldr		r2,[r1]
	bic		r2,r2,#1	; The lowest bit is cleared ,bit0=0
	str		r2,[r1]
	; Call delay function delay_B-- With parameters 
	ldr		r0,=0x30d40	;0x30d40=200000, Save the parameters in R0 in 
	bl		delay_B	; Jump 
	;GPIO Output high level , The light goes out 
	ldr		r1,=0x40010C00
	add		r1,r1,#0X0c
	ldr		r2,[r1]
	orr		r2,r2,#1	;bit0 = 1
	str		r2,[r1]
	b	loop	; Jump to loop Realize the cycle 
	
Reset_Handler   PROC
				LDR     SP, =0x20000000+0x100
                BL      main
                ENDP
				END		
	

In order to understand CPU Functions of internal registers , Two delay functions are used , One has no parameters , no return value , Use it directly CPU Internal registers read and write data ; The other has parameters , There is a return value , Use stack to read and write data .

matters needing attention ：

1、 When a function is called , Jump command should use BL, The return address is saved to LR in , Otherwise, the function cannot return to the original address after execution .

2、 The parameters of the function are saved in R0-R3 in , Save the parameters in R0 in .

3、 For simple functions , The compiler will optimize , Data is stored directly in internal registers ,CPU Direct operation of internal registers , Efficient . For complex functions , The data will be put on the stack , Data is taken out of the stack , Put it back on the stack .

4、ldr,str Such as instruction , Square brackets indicate that the operation is the data of the address stored in the internal register in square brackets . The change is R0 The data pointed to by the saved address , instead of R0 Data in .

2、C Language to achieve key control LED

Just like before LED The experiment is similar , The same is true for keys . Here key connection PA0 Pin , Press the key ,PA0 Low level ; Release the button ,PA0 High level .

1、 Can make GPIOA.

2、 Set up PA0 The pin is in input mode .

3、 Read GPIOA Input data register , obtain PA0 Pin status of .

GPIO Before the clock enable register and the working mode configuration register LED It was introduced in the experiment , There is no explanation here , So let's talk about that GPIO Data register GPIOX_IDR .

You can see , This is a 32 Bit register , low 16 Bit effective , preservation PIN0-15 Current state of each pin , above-mentioned , This register can only read all values , Cannot read by bit .

Here is the procedure , First, define the pointer to all the registers used , Then through bit operation , Modify the value of the register , stay while In circulation , Read GPIOA_IDR Value , And to 0 Bit to judge , if bit0=1, explain PA0 This is the high level , Release the button , The light goes out ; if bit0=0, explain PA0 At this time, it is low level , Press the key , Light on .

int main(void)
{
    
	unsigned int * pAPB2En = ( unsigned int * )(0x40021000 + 0x18);
	unsigned int * pGPIOBCrl = ( unsigned int * )(0x40010C00 + 0);
	unsigned int * pGPIOACrl = ( unsigned int * )(0x40010800 + 0x00);
	unsigned int * pGPIOOdr = ( unsigned int * )(0x40010C00 + 0X0c);
	unsigned int * pGPIOIdr = ( unsigned int * )(0x40010800 + 0x08);
	*pAPB2En |= (3<<2);	// Can make GPIO_A_B
	* pGPIOBCrl |= (1<<0);	//PB0 Set the output mode 
	* pGPIOACrl |= (1<<2);	//PA0 Set to input mode 
	* pGPIOOdr |= (1<<0);	//PB0=1, The light goes out 
	while(1)
	{
    
		if((* pGPIOIdr) & (1<<0) == 1)	//PA0=1, Release the button 
		{
    
			* pGPIOOdr |= (1<<0);	//PB0=1, The light goes out 
		}
		else	//PA0=0, Press the key 
		{
    
			* pGPIOOdr &= ~(1<<0);	//PB0=0, Light on 
		}
	}
}