1. Mx6u-alpha development board (LED drive experiment in C language version)

One 、C Language runtime environment test

.global _start  		/*  Global label  */

_start:
	/*  Get into SVC Pattern  */
	mrs r0, cpsr
	bic r0, r0, #0x1f 	/*  take r0 Low in register 5 A reset , That is to say cpsr Of M0~M4*/
	orr r0, r0, #0x13 	/* r0 Or on the 0x13, Said the use of SVC Pattern */
	msr cpsr, r0		/*  take r0  Data written to cpsr_c in */

	ldr sp, =0X80200000	/*  Set the stack pointer */
	b main				/*  Jump to main function  */

One 、 Set processor mode

​ Set up 6ULL be in SVC Pattern Next . Set up CPSR The register of bit4-0, That is to say M[4:0] by 10011=0X13. Reading and writing the status register requires MRS and MSR Instructions .MRS take CPSR The register data is read into the general-purpose register ,MSR The instruction writes the value of the general-purpose register to CPSR Go inside the register .

Two 、 Set up sp The pointer

​ Sp Can point to the inside RAM, You can also point to DDR, We point it to DDR.Sp Where to set ？512MB The scope of the 0x80000000~0x9FFFFFFF. Stack size ,0x200000=2MB. Processor stack growth mode , about A7 In general, it is growing downward . Set up sp Point to 0x80200000.

3、 ... and 、 Jump to C Language

​ Use b Instructions , Jump to C Language functions , such as main function .

Two 、 Software writing

#ifndef __MAIN_H
#define __MAIN_H
/* * CCM Related register address  */
#define CCM_CCGR0 *((volatile unsigned int *)0X020C4068)
#define CCM_CCGR1 *((volatile unsigned int *)0X020C406C)

#define CCM_CCGR2 *((volatile unsigned int *)0X020C4070)
#define CCM_CCGR3 *((volatile unsigned int *)0X020C4074)
#define CCM_CCGR4 *((volatile unsigned int *)0X020C4078)
#define CCM_CCGR5 *((volatile unsigned int *)0X020C407C)
#define CCM_CCGR6 *((volatile unsigned int *)0X020C4080)

/* * IOMUX Related register address  */
#define SW_MUX_GPIO1_IO03 *((volatile unsigned int *)0X020E0068)
#define SW_PAD_GPIO1_IO03 *((volatile unsigned int *)0X020E02F4)

/* * GPIO1 Related register address  */
#define GPIO1_DR *((volatile unsigned int *)0X0209C000)
#define GPIO1_GDIR *((volatile unsigned int *)0X0209C004)
#define GPIO1_PSR *((volatile unsigned int *)0X0209C008)
#define GPIO1_ICR1 *((volatile unsigned int *)0X0209C00C)
#define GPIO1_ICR2 *((volatile unsigned int *)0X0209C010)
#define GPIO1_IMR *((volatile unsigned int *)0X0209C014)
#define GPIO1_ISR *((volatile unsigned int *)0X0209C018)
#define GPIO1_EDGE_SEL *((volatile unsigned int *)0X0209C01C)

#endif

#include "main.h"
/* Enable peripheral clock */
void clk_enable(void)
{
    
    CCM_CCGR1 = 0xFFFFFFFF;
    CCM_CCGR2 = 0xFFFFFFFF;
    CCM_CCGR3 = 0xFFFFFFFF;
    CCM_CCGR4 = 0xFFFFFFFF;
    CCM_CCGR5 = 0xFFFFFFFF;
    CCM_CCGR6 = 0xFFFFFFFF;
}

/* initialization LED*/
void led_init(void)
{
    
    SW_PAD_GPIO1_IO03 = 0x5;/* Reuse as GPIO1-IO03*/
    SW_PAD_GPIO1_IO03 = 0x10B0;/* Set up GPIO1——IO03 Electrical properties */

    /*GPIO initialization */
    GPIO1_GDIR = 0x8;/* Set as output */
    GPIO1_DR = 0x0;/* open LED The lamp */
}

/* Short delay */
void delay_short(volatile unsigned int n)
{
    
    while(n--){
    }
}

void delay(volatile unsigned int n)
{
    
    while(n--)
    {
    
        delay_short(0x77f); //1 millisecond （396MHZ）
    }
}

void led_on(void)
{
    
    GPIO1_DR &= ~(1<<3);
}

void led_off(void)
{
    
    GPIO1_DR |= (1<<3);
}


int main(void)
{
    
    clk_enable();
    led_init();
    while(1)
    {
    
        led_on();
        delay(500);

        led_off();
        delay(500);
    }
    return 0;
}

3、 ... and 、 Link script

​ The link script describes the file to be connected , And link order , And the first address of the link
​ The syntax of the link script is simple , Is to write a series of commands , These commands make up the link script , Each command is a keyword with parameters or an assignment to symbols , You can use semicolons to separate commands . Strings such as file names can be typed directly , You can also use wildcards “*”. The simplest link script can contain only one command “SECTIONS”, We can be here “SECTIONS” Inside to describe the memory layout of the output file . Generally, the compiled code is included in text、data、bss and rodata In these four paragraphs ,

Our link script requirements for this experiment are as follows ：

①、 The starting address of the link is 0X87800000

②、start.o To be linked to the beginning , because start.o It contains the first command to execute

According to the requirements , stay Makefile Create a new directory named “imx6ul.lds” The file of , Then enter the following code in this file ：

SECTIONS{
	. = 0X87800000;
	.text :
	{
		start.o 
		main.o 
		*(.text)
	}
	.rodata ALIGN(4) : {*(.rodata*)}     
	.data ALIGN(4)   : { *(.data) }    
	__bss_start = .;    
	.bss ALIGN(4)  : { *(.bss)  *(COMMON) }    
	__bss_end = .;
}

​ The first 1 OK, let's write a keyword first “SECTIONS”, Followed by a brace , This brace and the second 14 The braces of the line are a pair , It's a must . It looks like C The functions in the language are the same .

​ The first 2 Line pair a special symbol “.” Assign a value ,“.” It is called location counter in link script , The default positioning counter is 0. We ask the code to link to 0X87800000 Where is the starting address , So this line gives “.” assignment 0X87800000, Said to 0X87800000 Start , Subsequent files or paragraphs will be marked with 0X87800000 Start the link for the starting address .

​ The first 3 Yes “.text” Is the segment name , The following colon is the syntax requirement , You can fill in the braces after the colon to link to “.text” All the files in this section ,“(.text)” Medium “” The wildcard , Representing all input files .text Put all the paragraphs in “.text” in .

​ The first 5 Line sets the file linked to the start location to start.o, because start.o It contains the first instruction to be executed , So be sure to link to the beginning . The first 6 Line is main.o This file , In fact, you don't have to write it out , because main.o It doesn't matter where you are , It is up to the compiler to determine the link location .

​ The first 10 Line defines a name called “.data” Section of , Then all the files “.data” Put all the paragraphs here .ALIGN(4) It's for the right “.data” The beginning of this paragraph
The starting address is byte aligned ,ALIGN(4) Express 4 Byte alignment . That is to say, paragraph “.data” The starting address should be able to be 4 to be divisible by , The common ones are ALIGN(4) perhaps ALIGN(8), That is to say 4 Byte or 8 Byte alignment .

​ In the 11、13 Yes __bss_start and __bss_end It's the sign , The first 11、13 These two lines are actually assigning values to these two symbols , Its value is the locator “.”, These two symbols are used to save .bss The starting and ending addresses of the segment ..bss A segment is a variable that is defined but not initialized , We need to do it manually .bss Segment variables are cleared , So we need to know .bss Start and end addresses of segments , In this way, we directly assign... To this memory 0 You can complete clearing . Pass the first 11、13 Line code ,.bss The start address and end address of the segment are saved in __bss_start and __bss_end in , We can directly compile or C These two symbols are used in the file .

After execution LED flashing