Handle GPIO in User Space ARM9 Embedded Linux AM1808 - embedded

Question

I have to interface my GSM module with the AM1808 based on ARM9.
I have assigned all the GPIO pins to the Da850.c as well as mux.h files. I successfully created a uImage and inserted that image in my flash.
I need to handle some of that GPIO from User application.
I know that we can handle the GPIO from the Kerel space but i need to handle from the user space.
As for example I have assigned a GPIO for power key to GSM module. I need to change the pin means (HIGH or LOW) through application.
Ok i have written a following code to access it from the User Space,
#include <stdio.h>
#include <time.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <unistd.h>
#include "GSMpwr.h"
#define BS_GSM_PWR_REGISTER 0x01E26014
#define BS_DCDS_MASK 0x00000004
int fd; // Memory device descriptor
unsigned long *pPWR;
unsigned short GetGSMpwr(void)
{
#if defined __HOST_ARM
unsigned long dcd_value = *pPWR;
return (pwr_value >> 7) & 0x01;
#endif
}
void InitializeGSMpwr(void)
{
#if defined __HOST_ARM
int page_size = getpagesize();
unsigned int MAP_addr;
unsigned int reg_addr;
unsigned char *pTemp; // Pointer to GSMpwr register
/*
* Open memory and get pointer to GSMpwr register in the FPGA
*/
if((fd = open("/dev/mem", O_RDWR | O_SYNC)) < 0)
{
printf("failed to open /dev/mem");
return;
}
else
{
MAP_addr = (BS_GSM_PWR_REGISTER & ~(page_size - 1));
pTemp = (unsigned char *)mmap(NULL, page_size,(PROT_READ | PROT_WRITE),MAP_SHARED,fd,MAP_addr);
if((pTemp == MAP_FAILED) || (pTemp == NULL))
{
printf("failed to map /dev/mem");
return;
}
else
{
printf(“Memory Mapped at Address %p. \n”,pTemp);
}
virt_addr = map_base + (control & MAP_MASK);
reg_addr = (BS_GSM_PWR_REGISTER & (page_size - 1));
pPWR = (unsigned long*)(pTemp + reg_addr);
printf("GSM PWR PIN mapped in Application\n");
}
I can only read that pin through this code, Now i want to use that pin as an output and want to go high and low with the time interval of 3sec.

Answer 1

The easiest way is to utilize GPIO support in sysfs, where you could control all the exported GPIO's. Please have a look at the Linux kernel GPIO documentation, in particular, Sysfs Interface for Userspace part.
After you have enabled GPIO support in sysfs (GPIO_SYSFS), the GPIO control would be as easy as:
Example
GPIO=22
cd /sys/class/gpio
ls
echo $GPIO > /sys/class/gpio/export
ls
Notice on the first ls that gpio22 doesn't exist, but does after you export GPIO 22 to user space.
cd /sys/class/gpio/gpio$GPIO
ls
There are files to set the direction and retrieve the current value.
echo "in" > direction
cat value
You can configure the GPIO for output and set the value as well.
echo "out" > direction
echo 1 > value
Example is taken from here.

Answer 2

I got it please find following code for that,I got the Specific pin address and i have accessed that pin like,
unsigned short GetGSMpwr(void)
{
unsigned long pwr_value = *pPWR;
printf("GSM_PWR:check Start : %ld",pwr_value);
return (pwr_value >> 1) & 0x01;
}
unsigned short SetGSMpwr(void)
{
unsigned long pwr_value = *pPWR;
printf("GSM_PWR:check Start : %ld",pwr_value);
*pPWR = ~((pwr_value >> 1) & 0x01);
}
unsigned short ClrGSMpwr(void)
{
unsigned long pwr_value = *pPWR;
printf("GSM_PWR:check Start : %ld",pwr_value);
*pPWR = 256;
}`