# GPIO Command-Line Tool in C

A simple command-line tool written in C to control Raspberry Pi GPIO pins using the Linux GPIO `sysfs` interface.

The program supports configuring a GPIO as an **input** or **output**, writing a digital value, and reading the state of an input.

## Compile

Compile the program using GCC:

```bash
gcc main.c -o gpio
```

## Usage

The general command syntax is:

```bash
./gpio <gpio> <direction> [value]
```

### GPIO as Output

Configure GPIO 17 as an output and set it HIGH:

```bash
./gpio 17 out 1
```

Set GPIO 17 LOW:

```bash
./gpio 17 out 0
```

When `out` is selected, the value argument is required:

```text
./gpio <gpio> out <0|1>
```

For example, the following command is invalid:

```bash
./gpio 17 out
```

because the output value is missing.

### GPIO as Input

Configure GPIO 17 as an input and read its current digital state:

```bash
./gpio 17 in
```

The program reads the GPIO `value` file and displays either:

```text
0
```

or:

```text
1
```

No additional value argument is required for an input.

## Program Flow

The program follows this sequence:

```text
Command-line arguments
        │
        ▼
Validate direction
        │
        ├── out → verify value argument
        │
        └── in  → no value required
        │
        ▼
Export GPIO
        │
        ▼
Set GPIO direction
        │
        ├── out → gpio_write()
        │
        └── in  → gpio_read()
        │
        ▼
Unexport GPIO
```

## Functions

The program is divided into the following functions:

```c
int gpio_export(const char *gpio);
int gpio_direction(const char *gpio, const char *direction);
int gpio_write(const char *gpio, const char *value);
int gpio_read(const char *gpio);
int gpio_unexport(const char *gpio);
```

Their responsibilities are:

- `gpio_export()` — exports the selected GPIO.
- `gpio_direction()` — configures the GPIO as `in` or `out`.
- `gpio_write()` — writes `0` or `1` to an output.
- `gpio_read()` — reads the digital state of an input.
- `gpio_unexport()` — releases the GPIO after the operation.

## GPIO sysfs Files

For GPIO 17, the program accesses files such as:

```text
/sys/class/gpio/chip0/gpio17/direction
/sys/class/gpio/chip0/gpio17/value
```

The `direction` file determines whether the GPIO is configured as an input or output.

The `value` file is used to read or write the digital state of the GPIO.

## Example

Output:

```bash
./gpio 17 out 1
```

Input:

```bash
./gpio 17 in
```

Invalid output command:

```bash
./gpio 17 out
```

Expected error:

```text
Error: GPIO out option requires a value.
Usage: ./gpio <gpio> out <0|1>
```

## Current Features

- GPIO export and unexport
- Input/output direction configuration
- Digital output (`0` or `1`)
- Digital input reading
- Command-line argument validation
- Invalid direction detection

## Future Work

A future version will include a `blink` operation:

```bash
./gpio 17 blink 500
```

where `500` represents the blinking interval in milliseconds.

This version now reflects the structure of your current C implementation, including the separation between argument validation and GPIO operations.