S3C2440 bare metal review ------ GPIO

After reading the S3C2440 bare metal for the first time, I have forgotten some of them, so I will select a few to review, starting with GPIO.

1 Schematic

First, we need to look at the schematic diagram. We can see that we can light up LED1 by setting GPF4 to a low level.

2 Chip Manual

From the chip manual, we can see that we need to set [9:8] of the GPFCON register to 01, and then set [4] of the GPFDAC to 0.

3 Assembly language lights up LED

3.1 start.S

.test

.global _start

    mov 0x56000050 #0x100

    mov ox56000054 #0x10

.halt

    b halt

 3.2 Makefile

all:

arm-linux-gcc -c start.S -o start.o

arm-linux-ld -Ttext 0 start.o -o start.elf

arm-linux-objcopy -O binary -S start.elf start.binary

clean:

rm *.bin *.o *.elf

3.3 Compile and debug

Compilation found various errors

 Text is written as test, "halt:" is written as ".halt". And the mov assignment is also wrong.

The modified start.S is as follows

.text

.global _start

    /*Configure GPF4 as output*/

    ldr r0,=0x56000050

    ldr r1, =0x100

    str r1,[r0]

    /*Configure GPF4 to output low level*/

    ldr r0,=0x56000054

    ldr r1, =0xff

    str r1,[r0]

halt:

    b halt

4 C language lights up LED

Next, use C language to light up the LED, and add the code to close the door, and set the stack to support both nandflash startup and norflash startup.

First modify start.S

.text

.global _start

    /*turn off watchdog*/

    ldr r0, =0x53000000

    ldr r1, =0x0

    str r1,[r0]

    /*Set up the stack,

    Write 0 to address 0, and then read it out. If 0 is obtained, it means that the content at address 0 has been modified, then NOR is started.

    Otherwise, nand starts*/

    mov r1, #0

    ldr r0, [r1] /*Read out the original value backup*/

    str r1, [r1]

    ldr r2,[r1]

    cmp r1,r2

    ldr sp,=0x40000000+4096 /*Assume that nand is started*/

    moveq sp,#4096

    streq r0,[r1] /*Restore the original value*/

    bl main

halt:

    b halt

Then led.c

#include "s3c2440_soc.h"

void delay(volatile int d)

{

while (d--);

}

/*Loop to light up the LED*/

int main(){

    int val = 0;

    int temp = 0;

    /*First configure GPIO as output*/

    GPFCON &= ~((3<<8) | (3<<10) | (3<<12)); // Clear

    GPFCON |= ((1<<8) | (1<<10) | (1<<12));

    while(1){

        temp = ~val; //We want all three lights to be off when the value is 0, but they are actually on when the level is low, so we invert it.

        temp &= 7; //We only care about three bits, and ignore the other bits.

        GPFDAT &= ~(7<<4); // clear to zero first

        GPFDAT |= (temp<<4);

        delay(100000);

        val++;

        if(8 == val)

            val =0;

    }

}