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@ -1,182 +1,10 @@
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# GPIO Command-Line Tool in C
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A simple command-line tool written in C to control Raspberry Pi GPIO pins using the Linux GPIO `sysfs` interface.
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The program supports configuring a GPIO as an **input** or **output**, writing a digital value, and reading the state of an input.
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## Compile
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Compile the program using GCC:
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```bash
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gcc main.c -o gpio
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```
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## Usage
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The general command syntax is:
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```bash
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./gpio <gpio> <direction> [value]
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```
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### GPIO as Output
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Configure GPIO 17 as an output and set it HIGH:
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```bash
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./gpio 17 out 1
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```
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Set GPIO 17 LOW:
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```bash
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./gpio 17 out 0
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```
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When `out` is selected, the value argument is required:
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```text
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./gpio <gpio> out <0|1>
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```
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For example, the following command is invalid:
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```bash
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./gpio 17 out
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```
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because the output value is missing.
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### GPIO as Input
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Configure GPIO 17 as an input and read its current digital state:
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# Introduction
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How to compile
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```bash
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./gpio 17 in
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```
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The program reads the GPIO `value` file and displays either:
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```text
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0
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```
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or:
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```text
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1
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gcc main.c -o hello
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```
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No additional value argument is required for an input.
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## Program Flow
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The program follows this sequence:
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```text
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Command-line arguments
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│
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▼
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Validate direction
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│
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├── out → verify value argument
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│
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└── in → no value required
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│
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▼
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Export GPIO
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│
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▼
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Set GPIO direction
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│
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├── out → gpio_write()
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│
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└── in → gpio_read()
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│
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▼
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Unexport GPIO
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```
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## Functions
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The program is divided into the following functions:
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```c
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int gpio_export(const char *gpio);
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int gpio_direction(const char *gpio, const char *direction);
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int gpio_write(const char *gpio, const char *value);
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int gpio_read(const char *gpio);
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int gpio_unexport(const char *gpio);
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```
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Their responsibilities are:
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- `gpio_export()` — exports the selected GPIO.
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- `gpio_direction()` — configures the GPIO as `in` or `out`.
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- `gpio_write()` — writes `0` or `1` to an output.
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- `gpio_read()` — reads the digital state of an input.
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- `gpio_unexport()` — releases the GPIO after the operation.
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## GPIO sysfs Files
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For GPIO 17, the program accesses files such as:
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```text
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/sys/class/gpio/chip0/gpio17/direction
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/sys/class/gpio/chip0/gpio17/value
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```
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The `direction` file determines whether the GPIO is configured as an input or output.
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The `value` file is used to read or write the digital state of the GPIO.
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## Example
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Output:
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```bash
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./gpio 17 out 1
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```
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Input:
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```bash
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./gpio 17 in
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```
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Invalid output command:
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```bash
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./gpio 17 out
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```
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Expected error:
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```text
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Error: GPIO out option requires a value.
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Usage: ./gpio <gpio> out <0|1>
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```
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## Current Features
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- GPIO export and unexport
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- Input/output direction configuration
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- Digital output (`0` or `1`)
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- Digital input reading
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- Command-line argument validation
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- Invalid direction detection
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## Future Work
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A future version will include a `blink` operation:
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```bash
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./gpio 17 blink 500
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```
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where `500` represents the blinking interval in milliseconds.
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This version now reflects the structure of your current C implementation, including the separation between argument validation and GPIO operations.
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# Issues
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- [ ] Error catcher
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@ -1,142 +1,66 @@
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// Gerardo Marx 24/09/2026
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// gpio command tool
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// eg. ./gpio 17 out 1
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// ./gpio 17 in
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// ./gpio 17 blink 500(ms)
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#include <stdio.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <string.h>
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// prototype functions
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int gpio_export(const char *gpio);
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int gpio_direction(const char *gpio, const char *direction); // this function
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int gpio_write(const char *gpio, const char *value); // write function
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int gpio_read(const char *gpio); //read function
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int gpio_unexport(const char *gpio);
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int main(int argc, char *argv[]){
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int fd;
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const char *pin;
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const char *dir;
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const char *val = NULL;
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// checking that at least gpio and direction is passed
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if(argc<3){
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printf("Usage:\n");
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printf(" %s <gpio> in\n", argv[0]);
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printf(" %s <gpio> out <value>\n", argv[0]);
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return 1;
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}
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pin = argv[1]; // get gpio number from argument
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dir = argv[2]; // get gpio direction from arguments
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//const char *val = argv[3];
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// checking the gpio direction
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if(strcmp(dir, "out") == 0) {
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if(argc<4){
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printf("Error: GPIO out option requires a value.\n");
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printf("Usage: %s <gpio> out <0|1>\n", argv[0]);
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return 1;
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}
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val = argv[3];
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}
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// performing the read/write operation
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gpio_export(pin);
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gpio_direction(pin, dir);
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//gpio_write(pin, val);
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if (strcmp(dir,"out") == 0) {
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gpio_write(pin, val);
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} else if (strcmp(dir, "in") == 0) {
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gpio_read(pin);
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} else {
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perror("invalid direction argument\n");
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return -12;
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}
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gpio_unexport(pin);
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}
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// comple functions
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//
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// gpio_export
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int gpio_export(const char *gpio){
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int fd;
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// export
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fd = open("/sys/class/gpio/chip0/export", O_WRONLY);
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if(fd<0){
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perror("Error opening the GPIO path during export");
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if(fd<0)
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{
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perror("Error opening the GPIO path");
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return -1;
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}
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write(fd,gpio,strlen(gpio));
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close(fd);
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return 0;
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}
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// gpio direction
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int gpio_direction(const char *gpio, const char *direction){
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// pin direction - convert into functions
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int fd;
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char path[64];
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snprintf(path, sizeof(path),
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"/sys/class/gpio/chip0/gpio%s/direction", gpio);
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fd = open(path, O_WRONLY); //gpio number
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write(fd,"17",2);
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close(fd);
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// pin direction
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fd = open("/sys/class/gpio/chip0/gpio17/direction", O_WRONLY);
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if(fd<0)
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{
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perror("Error opening the GPIO path");
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return -1;
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}
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write(fd,direction,strlen(direction));
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write(fd,"out",3);
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close(fd);
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return 0;
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}
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int gpio_write(const char *gpio, const char *value){
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int fd;
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char path[64];
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snprintf(path, sizeof(path),
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"/sys/class/gpio/chip0/gpio%s/value", gpio);
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fd = open(path, O_WRONLY);
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if(fd<0){
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perror("Error opening the GPIO path during write");
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// pin value to 1
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fd = open("/sys/class/gpio/chip0/gpio17/value", O_WRONLY);
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if(fd<0)
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{
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perror("Error opening the GPIO path");
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return -1;
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}
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if(write(fd,value, strlen(value)) < 0) {
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perror("write");
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close(fd);
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write(fd,"1",1);
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close(fd);
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sleep(1);
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// pin valu to 0
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fd = open("/sys/class/gpio/chip0/gpio17/value", O_WRONLY);
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if(fd<0)
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{
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perror("Error opening the GPIO path");
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return -1;
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}
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//write(fd, value, strlen(value));
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write(fd,"0",1);
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close(fd);
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return 0;
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}
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// gpio read
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int gpio_read(const char *gpio){
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printf(" Test read function for gpio %s\n", gpio);
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return 0;
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}
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// unexport
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int gpio_unexport(const char *gpio){
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int fd;
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sleep(1);
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// unexport
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fd = open("/sys/class/gpio/chip0/unexport", O_WRONLY);
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if(fd<0)
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{
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perror("Error opening the GPIO path during unexport");
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return -1;
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}
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if(write(fd,gpio, strlen(gpio)) < 0) {
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perror("unexport");
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close(fd);
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perror("Error opening the GPIO path");
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return -1;
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}
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write(fd,"17",2);
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close(fd);
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printf("Hello from Raspberry Pi!\n");
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printf("Number of arguments: %d\n", argc);
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printf("Program is reciving: %s\n", argv[0]);
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if(argc > 1 )
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printf("Argument: %s\n", argv[1]);
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return 0;
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}
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