Writing to an I/O Address - c

Question

I am using a VersaLogic Osprey Board and I am running Lubuntu 16.04 Xenial with GCC compiler 6.2.0. Writing in C, I cannot compile C++.
I am trying to read from the I/O address of the Watchdog timer, with the intent of later enabling it. According to the data sheet the I/O address is 1CA8 (WDT_CTL is the identifier of this address)
The code I have thus far is as follows:
#define WDT_CTL 0x1CA8
int main(void)
{
char *p_CTL = (char*) WDT_CTL;
printf("Attempting to print contents %c\n"),*p_CTL);
}
The code compiles, but I get a segmentation fault (core dumped) when I get to the important line, there are no other errors or warnings. As far as I know a seg fault is a "you can't access that memory location" error, but I am trying to read from the address that I found in the data sheet.
I have done some research and according to the datasheet the address I have is an I/O address, which seems to be different from a normal address. When I look at the address of a custom variable (char a) that address is 12 digits long as opposed to the four I am given for the watchdog timer.
Am I missing something? Is it a limitation of Lubuntu that I can no longer write directly to an I/O address? Do I need to use some specific command to do so? Do I need to enable something or change a setting?
Note that this thread is different from one with a similar title because that was done in Windows 7, not Lubuntu and that fix will not work here.

Answer 1

This is how I usually access the watchdog hardware:
This has worked on several different computers.
#include "watchdog.h"
#include <fcntl.h> /* open() */
#include <stdio.h> /* printf() */
#include <unistd.h> /* write() */
#include <string.h> /* strerror() */
#include <errno.h> /* errno */
#define APP_VERSION "1.1.0"
/* Look for the device in two places */
#define WD_KICK_DEV_NAME_1 "/dev/cs5535/gpio/5"
#define WD_KICK_DEV_NAME_2 "/dev/gpio/5"
#define WD_ENABLE_DEV_NAME_1 "/dev/cs5535/gpio/27"
#define WD_ENABLE_DEV_NAME_2 "/dev/gpio/27"
#define TEXT_WDOG_KICK "Ot0101"
#define TEXT_WDOG_ENABLE "1TO"
#define TEXT_WDOG_DISABLE "0TO"
static INT32 wd_kick_fd;
static INT32 wd_enable_fd;
/**
* Return the version
*/
const char *wd_get_version(void)
{
return(APP_VERSION);
}
/**
* Open GPIO-5 and GPIO-27
*/
INT32 wd_init(void)
{
if (((wd_kick_fd = open(WD_KICK_DEV_NAME_2, O_WRONLY)) < 0) &&
((wd_kick_fd = open(WD_KICK_DEV_NAME_1, O_WRONLY)) < 0))
{
printf("Failed to open '%s' or '%s': %s (%d)\n",
WD_KICK_DEV_NAME_1, WD_KICK_DEV_NAME_2, strerror(errno), errno);
return(FAILURE);
}
if (((wd_enable_fd = open(WD_ENABLE_DEV_NAME_2, O_WRONLY)) < 0) &&
((wd_enable_fd = open(WD_ENABLE_DEV_NAME_1, O_WRONLY)) < 0))
{
printf("Failed to open '%s' or '%s': %s (%d)\n",
WD_ENABLE_DEV_NAME_1, WD_ENABLE_DEV_NAME_2, strerror(errno), errno);
return(FAILURE);
}
return(SUCCESS);
}
/**
* Disabled via GPIO-27
*/
void wd_disable(void)
{
(void)write(wd_enable_fd, TEXT_WDOG_DISABLE, strlen(TEXT_WDOG_DISABLE));
}
/**
* Enabled via GPIO-27
*/
void wd_enable(void)
{
(void)write(wd_enable_fd, TEXT_WDOG_ENABLE, strlen(TEXT_WDOG_ENABLE));
}
/**
* Kick the watchdog by toggling GPIO 5
*/
void wd_kick(void)
{
(void)write(wd_kick_fd, TEXT_WDOG_KICK, strlen(TEXT_WDOG_KICK));
}
and the watchdog.h file contains:
#ifndef WATCHDOG_H_INCLUDED
#define WATCHDOG_H_INCLUDED
/**
* Grab the version of the kicker stuff
*/
const char *wd_get_version(void);
/**
* Do any initialization needed for the watchdog.
*
* #return SUCCESS or FAILURE
*/
INT32 wd_init(void);
/**
* Disables the watchdog.
* If watchdog cannot be disabled, then calls wd_kick()
*/
void wd_disable(void);
/**
* Enables the watchdog.
* If watchdog cannot be disabled, do nothing.
*/
void wd_enable(void);
/**
* Kicks the watchdog
*/
void wd_kick(void);
#endif /* WATCHDOG_H_INCLUDED */