Skip to content

Instantly share code, notes, and snippets.

@sjgallagher2

sjgallagher2/embedded_linux_gpio1.c

Created July 2, 2025 20:39
Show Gist options

  • Select an option

    Learn more about clone URLs
  • Save sjgallagher2/fe348e618f56724255fd37d31e45542b to your computer and use it in GitHub Desktop.

Select an option

Learn more about clone URLs
Save sjgallagher2/fe348e618f56724255fd37d31e45542b to your computer and use it in GitHub Desktop.
Download ZIP
Raw
embedded_linux_gpio1.c
// Printing and file handling
#include <stdio.h>
#include <string.h>
// Function doc template:
/**
* @brief Summary.
*
* Long description.
*
* @param name Description.
* @return Return description.
*/
typedef enum{
GPIO_DIR_INPUT=0,
GPIO_DIR_OUTPUT
} GPIO_DIRECTION;
typedef enum{
GPIO_LOW=0,
GPIO_HIGH
} GPIO_VALUE;
typedef enum{
GPIO_EDGE_NONE,GPIO_EDGE_RISING,GPIO_EDGE_FALLING,GPIO_EDGE_BOTH
} GPIO_EDGE;
typedef enum{
GPIO_PROP_DIRECTION,GPIO_PROP_EDGE,GPIO_PROP_LABEL,GPIO_PROP_VALUE,GPIO_PROP_ACTIVE_LOW
} GPIO_PROPERTIES;
typedef struct{
int number;
GPIO_DIRECTION dir;
int debounce_time;
} gpio_pin;
// Private functions
int _gpio_get_filename(gpio_pin* gpio,char* fname,GPIO_PROPERTIES prop);
int _gpio_write(gpio_pin* gpio,GPIO_PROPERTIES prop,char* value);
int _gpio_read(gpio_pin* gpio,GPIO_PROPERTIES prop,char* value);
// Public functions
int gpio_set_direction(gpio_pin* gpio,GPIO_DIRECTION dir);
GPIO_DIRECTION gpio_get_direction(gpio_pin* gpio);
int gpio_set_value(gpio_pin* gpio,GPIO_VALUE val);
int gpio_toggle_output(gpio_pin* gpio);
GPIO_VALUE gpio_get_value(gpio_pin* gpio);
int gpio_set_active_low(gpio_pin* gpio);
int gpio_set_active_high(gpio_pin* gpio);
// Software debounce only
void gpio_set_debounce_time(gpio_pin* gpio,int time){gpio->debounce_time = time;}
int _gpio_get_filename(gpio_pin* gpio,char* fname,GPIO_PROPERTIES prop)
{
/**
* @brief Generates a filename based on gpio number and property.
*
* This helper function does not check if the file actually exists.
*
* @param gpio gpio_pin struct pointer.
* @param fname filename buffer to be written to.
* @param prop GPIO property enum.
* @return 1 on success, -1 if property is not recognized.
*/
if(prop == GPIO_PROP_DIRECTION)
sprintf(fname, "/sys/class/gpio/gpio%d/%s",gpio->number,"direction");
else if(prop == GPIO_PROP_EDGE)
sprintf(fname, "/sys/class/gpio/gpio%d/%s",gpio->number,"edge");
else if(prop == GPIO_PROP_LABEL)
sprintf(fname, "/sys/class/gpio/gpio%d/%s",gpio->number,"label");
else if(prop == GPIO_PROP_VALUE)
sprintf(fname, "/sys/class/gpio/gpio%d/%s",gpio->number,"value");
else if(prop == GPIO_PROP_ACTIVE_LOW)
sprintf(fname, "/sys/class/gpio/gpio%d/%s",gpio->number,"active_low");
else
return -1;
return 1;
}
int _gpio_write(gpio_pin* gpio,GPIO_PROPERTIES prop,char* value)
{
/**
* @brief Writes a value to a GPIO pin property file.
*
* Uses the given gpio data and the desired property `prop`, builds the
* filename, and attempts to write `value` to that file.
*
* @param gpio gpio_pin struct pointer.
* @param prop GPIO property enum.
* @param value C string with value to be written to file
* @return 1 on success, -1 on failure.
*/
// Generate filename.
char filename[FILENAME_MAX];
int stat = _gpio_get_filename(gpio,filename,prop);
if(stat != 1)
{
printf("Unrecognized GPIO_PROPERTIES value %d\n",prop);
return -1;
}
// Open file.
FILE* fp = fopen(filename,"w");
if(!fp){
perror("File opening failed.");
printf("Check that the path is correct and that you have privileges for writing to it. The GPIO pin might not exist.\n");
return -1;
}
// Write to file.
int write_status = fputs(value,fp);
if(write_status == EOF)
{
printf("File writing failed with fputs(%s,%s)\n",value,filename);
printf("Check that you have privileges for writing.\n");
return -1;
}
// Close file.
fclose(fp);
// Return success.
return 1;
}
int _gpio_read(gpio_pin* gpio,GPIO_PROPERTIES prop,char* value)
{
/**
* @brief Reads the GPIO property into a buffer.
*
* Uses the given gpio data and the desired property `prop`, builds the
* filename, and attempts to read the contents into `value`.
*
* @param gpio gpio_pin struct pointer.
* @param prop GPIO property enum.
* @return Return 1 on success, -1 on failure.
*/
char filename[FILENAME_MAX];
int stat = _gpio_get_filename(gpio,filename,prop);
if(stat != 1)
{
printf("Unrecognized GPIO_PROPERTIES value %d\n",prop);
return -1;
}
// Open file.
FILE* fp = fopen(filename,"r");
if(!fp){
perror("File opening failed, check that the path is correct and that you have privileges for reading it. The GPIO pin might not exist. Error");
return -1;
}
// Read from file.
fgets(value,100,fp);
value[strcspn(value, "\n") ] = '\0'; // Remove line ending
// Close file.
fclose(fp);
// Return success.
return 1;
}
int gpio_set_direction(gpio_pin* gpio,GPIO_DIRECTION dir)
{
/**
* @brief Summary.
*
* Long description.
*
* @param gpio gpio_pin struct pointer.
* @return Return description.
*/
int write_status = -1;
if(dir == GPIO_DIR_INPUT)
{
write_status = _gpio_write(gpio,GPIO_PROP_DIRECTION,"in");
}
else if(dir == GPIO_DIR_OUTPUT)
{
write_status = _gpio_write(gpio,GPIO_PROP_DIRECTION,"out");
}
else write_status = -1;
return write_status;
}
GPIO_DIRECTION gpio_get_direction(gpio_pin* gpio)
{
/**
* @brief Summary.
*
* Long description.
*
* @param gpio gpio_pin struct pointer.
* @return Return description.
*/
char dir[10];
_gpio_read(gpio,GPIO_PROP_DIRECTION,dir);
if(strcmp(dir,"in") == 0)
{
return GPIO_DIR_INPUT;
}
else if(strcmp(dir,"out")==0)
{
return GPIO_DIR_OUTPUT;
}
return -1;
}
int gpio_set_value(gpio_pin* gpio,GPIO_VALUE val)
{
/**
* @brief Summary.
*
* Long description.
*
* @param gpio gpio_pin struct pointer.
* @return Return description.
*/
return 0;
}
int gpio_toggle_output(gpio_pin* gpio)
{
/**
* @brief Summary.
*
* Long description.
*
* @param gpio gpio_pin struct pointer.
* @return Return description.
*/
return 0;
}
GPIO_VALUE gpio_get_value(gpio_pin* gpio)
{
/**
* @brief Summary.
*
* Long description.
*
* @param gpio gpio_pin struct pointer.
* @return Return description.
*/
return GPIO_LOW;
}
int gpio_set_active_low(gpio_pin* gpio)
{
/**
* @brief Summary.
*
* Long description.
*
* @param gpio gpio_pin struct pointer.
* @return Return description.
*/
return 0;
}
int gpio_set_active_high(gpio_pin* gpio)
{
/**
* @brief Summary.
*
* Long description.
*
* @param gpio gpio_pin struct pointer.
* @return Return description.
*/
return 0;
}
int main()
{
// TESTS
// For these tests, use GPIO67 (PIN37). Here is its info:
// GPIO67 (unallocated)
// pin 37 (PIN37): ocp:P8_08_pinmux (GPIO UNCLAIMED) function pinmux_P8_08_default_pin group pinmux_P8_08_default_pin
// pin 37 (PIN37) 3:gpio-64-95 44e10894 00000037 pinctrl-single
// Pad config: 0x37 = 0 1 1 0 111 = fast, input/output, pullup, pull enable, mode 7
// GPIO settings:
// direction = in
// active_low = 0
// edge = none
// label = P8_08
// value = 1
gpio_pin gpio67;
gpio67.number = 67;
gpio67.dir = GPIO_DIR_INPUT;
// int _gpio_get_filename(gpio_pin* gpio,char* fname,GPIO_PROPERTIES prop);
/**
* @brief Generates a filename based on gpio number and property.
*
* This helper function does not check if the file actually exists.
*
* @param gpio gpio_pin struct pointer.
* @param fname filename buffer to be written to.
* @param prop GPIO property enum.
* @return 1 on success, -1 if property is not recognized.
*/
// Common test parameters //
char fname[FILENAME_MAX];
int stat = -999;
printf("1. Existing GPIO pin and property\n");
stat = _gpio_get_filename(&gpio67,fname,GPIO_PROP_DIRECTION);
printf("Filename for gpio67 direction: %s\n",fname);
printf("Status out: %d\n",stat);
printf("2. Existing GPIO pin but non-existent property\n");
stat = _gpio_get_filename(&gpio67,fname,999);
printf("Filename for gpio67 non-existent property: %s\n",fname);
printf("Status out: %d\n",stat);
printf("3. Non-existent GPIO pin and existing property\n");
gpio67.number = 999;
stat = _gpio_get_filename(&gpio67,fname,GPIO_PROP_DIRECTION);
printf("Filename for gpio67 (999) direction: %s\n",fname);
printf("Status out: %d\n",stat);
gpio67.number = 67;
printf("4. Non-existent GPIO pin and property\n");
gpio67.number = 999;
stat = _gpio_get_filename(&gpio67,fname,GPIO_PROP_DIRECTION);
printf("Filename for gpio67 (999) non-existent property: %s\n",fname);
printf("Status out: %d\n",stat);
gpio67.number = 67;
printf("\n");
// int _gpio_read(gpio_pin* gpio,GPIO_PROPERTIES prop,char* value)
/**
* @brief Reads the GPIO property into a buffer.
*
* Uses the given gpio data and the desired property `prop`, builds the
* filename, and attempts to read the contents into `value`.
*
* @param gpio gpio_pin struct pointer.
* @param prop GPIO property enum.
* @return Return 1 on success, -1 on failure.
*/
// Common test parameters //
char pindir[10];
stat = -999;
printf("1. Existing pin and property\n");
stat = _gpio_read(&gpio67,GPIO_PROP_DIRECTION,pindir);
printf("gpio67 direction: %s\n",pindir);
printf("Status out: %d\n",stat);
printf("2. Existing pin and non-existent property\n");
stat = _gpio_read(&gpio67,99,pindir);
printf("gpio67 bad property: %s\n",pindir);
printf("Status out: %d\n",stat);
printf("3. Non-existent pin and existing property\n");
gpio67.number = 999;
stat = _gpio_read(&gpio67,GPIO_PROP_DIRECTION,pindir);
printf("gpio67 (999) direction: %s\n",pindir);
printf("Status out: %d\n",stat);
gpio67.number = 67;
printf("4. Non-existent pin and property\n");
gpio67.number = 999;
stat = _gpio_read(&gpio67,999,pindir);
printf("gpio67 (999) bad property: %s\n",pindir);
printf("Status out: %d\n",stat);
gpio67.number = 67;
// int _gpio_write(gpio_pin* gpio,GPIO_PROPERTIES prop,char* value)
/**
* @brief Writes a value to a GPIO pin property file.
*
* Uses the given gpio data and the desired property `prop`, builds the
* filename, and attempts to write `value` to that file.
*
* @param gpio gpio_pin struct pointer.
* @param prop GPIO property enum.
* @param value C string with value to be written to file
* @return 1 on success, -1 on failure.
*/
// Common test parameters //
char pindir_set[] = "in";
stat = -999;
printf("1. Existing pin and property, attempting to write \"%s\"\n",pindir_set);
stat = _gpio_write(&gpio67,GPIO_PROP_DIRECTION,pindir_set);
printf("Attempting to read pin direction...\n");
_gpio_read(&gpio67,GPIO_PROP_DIRECTION,pindir);
printf("Read: %s\n",pindir);
printf("String comparison: %d\n",strcmp(pindir_set,pindir));
if(strcmp(pindir_set,pindir)==0)
{
printf("Success.\n");
}
else printf("Failure.\n");
printf("\n");
printf("2. Non-existent pin and existing property, attempting to write \"%s\"\n",pindir_set);
gpio67.number = 999;
stat = _gpio_write(&gpio67,GPIO_PROP_DIRECTION,pindir_set);
printf("Attempting to read pin direction...\n");
_gpio_read(&gpio67,GPIO_PROP_DIRECTION,pindir);
printf("Read: %s\n",pindir);
if(strcmp(pindir_set,pindir)==0)
{
printf("Success.\n");
}
else printf("Failure.\n");
gpio67.number = 67;
return 0;
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment