i. Construction of mx6ull C language environment

Catalog

One · Set processor mode

Two . Set up SP The pointer

3、 ... and . Link script

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One · Set processor mode

Set the processor to SVC In mode .

Set up CPSR The register of bit4-0, That is to say M[4：0] by 10011=0x13. The specific operations for reading and writing the status register are

MRS // take CPSR Register read to general purpose register 
MSR // Write the value in the general register to CPSR register 

( If you don't know what is svc Model students can read arm Architecture )    

Two . Set up SP The pointer

sp Can point to the inside RAM, You can also point to DDR, We point it to DDR.

With 6ull For example ,512MB Of DDR The address is 0x80000000-0x9fffffff... The stack size is 0x20000=2MB

commonly arm Schema code is growing downward .

So set sp Point to 0x800000000+ Stack size 0x20000=0x80020000

.global _start  		/*  Global label  */

/*
 *  describe ：	_start function , The program starts executing from this function , The main function of this function is to set C
 *		  Running environment .
 */
_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  		 */

Here, please refer to the code of zuozhongkai

If you use ddr The chip needs to be initialized first ddr You need to initialize in the startup file first ddr