Merge pull request #1 from fesolix/Kernel_Module

Kernel module

Kernel/Makefile

+obj-m := kernel_M.o
+KVERSION = $(shell uname -r)
+all:
+	make -C /lib/modules/$(KVERSION)/build M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(KVERSION)/build M=$(PWD) clean
\ No newline at end of file

Kernel/kernel_M.c

+#include <linux/init.h>
+#include <linux/module.h>
+
+#include <linux/kernel.h>
+#include <linux/fs.h>         // For file_operations
+#include <linux/uaccess.h>    // For copy_from_user
+#include <linux/cdev.h>       // For cdev
+#include <linux/device.h>     // For device_create, class_create
+#include <linux/slab.h>       // For kmalloc, kfree
+
+#include <linux/crc32.h>      // Include CRC32
+
+#include <linux/gpio.h>      // GPIO support
+#include <linux/delay.h>     // Delay functions
+#include <linux/jiffies.h>   // Time measurement
+
+#include <linux/kthread.h>   // Kernel threads
+#include <linux/sched.h>     // Task scheduling
+
+#define DEVICE_NAME "packet_receiver"
+#define CLASS_NAME  "packet_class"
+
+// cat /sys/kernel/debug/gpio
+#define GPIO_DATA 17  // GPIO for data transmission
+#define GPIO_CLOCK 27 // GPIO for clock control
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Me :)");
+MODULE_DESCRIPTION("A kernel module to receive packets from userspace.");
+MODULE_VERSION("1.7");
+
+// The size of the receive buffer
+#define RECV_BUF_SIZE 512
+
+// Global variables for device number, class, device.
+static dev_t dev_number;
+static struct class *packet_class = NULL;
+static struct cdev packet_cdev;
+
+// Store last valid data packet
+static char last_valid_packet[256] = {0}; 
+
+// Time of last transmission
+static struct task_struct *transmit_thread;
+
+// Flag to control loop in the thread
+static int keep_sending = 0;  
+
+// This buffer will temporarily store data from userspace
+static char *recv_buffer;
+
+// Forward declarations for file operations
+static int     packet_open(struct inode *inode, struct file *file);   //not used
+static int     packet_release(struct inode *inode, struct file *file);   //not used
+static ssize_t packet_read(struct file *filp, char __user *buf, size_t len, loff_t *offset);   //not used
+static ssize_t packet_write(struct file *filp, const char __user *buf, size_t len, loff_t *offset);
+static unsigned long calculate_crc32(const char *data, size_t len);
+static int transmit_loop(void *data); // Kernel thread function
+
+// File operations structure
+static struct file_operations fops = {
+    .owner   = THIS_MODULE,
+    .open    = packet_open,     //not used
+    .read    = packet_read,     //not used
+    .write   = packet_write,
+    .release = packet_release,  //not used
+};
+
+// CRC32 Calculation Function
+// uses the same polynomial as zlib’s standard CRC32
+static u32 calculate_crc32(const char *data, size_t len) {
+    return crc32(0, data, len);
+}
+
+// ====================== Device Open ======================
+static int packet_open(struct inode *inode, struct file *file) {
+    printk(KERN_INFO "packet_receiver: Device opened.\n");
+    return 0;
+}
+
+// ====================== Kernel Thread for Continuous Sending ======================
+static int transmit_loop(void *data) {
+    while (!kthread_should_stop()) {
+        if (keep_sending && strlen(last_valid_packet) > 0) {
+            // Wait for clock signal
+            if (gpio_get_value(GPIO_CLOCK) == 1) {
+                printk(KERN_INFO "packet_receiver: Clock HIGH -> Pausing transmission.\n");
+                msleep(100); // Small sleep to avoid busy looping
+                continue;
+            }
+
+            // Transmit the last valid packet
+            for (size_t i = 0; i < strlen(last_valid_packet); i++) {
+                gpio_set_value(GPIO_DATA, 1);
+                msleep(1);
+                gpio_set_value(GPIO_DATA, 0);
+                msleep(1);
+            }
+
+            printk(KERN_INFO "packet_receiver: Sent data to GPIO %d\n", GPIO_DATA);
+
+            // Wait 3x the transmission time before sending again
+            msleep(strlen(last_valid_packet) * 3);
+        } else {
+            msleep(100); // Wait if no valid packet
+        }
+    }
+    return 0;
+}
+
+// ====================== Device Read ======================
+static ssize_t packet_read(struct file *filp, char __user *buf, size_t len, loff_t *offset) {
+    printk(KERN_INFO "packet_receiver: Read called.\n");
+    return 0;
+}
+
+// ====================== Device Write ======================
+static ssize_t packet_write(struct file *filp, const char __user *buf, size_t len, loff_t *offset) {
+    // Bound the incoming size to the size of the buffer
+    size_t to_copy = min(len, (size_t)RECV_BUF_SIZE - 1);
+
+    // Clear the buffer before copying data into it (for safety)
+    memset(recv_buffer, 0, RECV_BUF_SIZE);
+
+    // Copy data from user space into recv_buffer 
+    if (copy_from_user(recv_buffer, buf, to_copy) != 0) {
+        printk(KERN_ERR "packet_receiver: copy_from_user failed.\n");
+        return -EFAULT;
+    }
+
+    // Ensure null-termination 
+    recv_buffer[to_copy] = '\0';
+
+    unsigned int sender_hex = 0;
+    int value_id_0 = -1, value_id_1 = -1;
+    char value_str_0[64] = {0};
+    char value_str_1[64] = {0};
+    unsigned long crc_val = 0;
+
+    printk(KERN_INFO "packet_receiver: Parsed fields [matches=%d]:\n", matches);
+    printk(KERN_INFO "  sender=0x%X\n", sender_hex);
+    printk(KERN_INFO "  value_id_0=%d  value_0=\"%s\"\n", value_id_0, value_str_0);
+    printk(KERN_INFO "  value_id_1=%d  value_1=\"%s\"\n", value_id_1, value_str_1);
+    printk(KERN_INFO "  crc=0x%lX\n", crc_val);
+
+    // Prepare the payload for CRC verification
+    char crc_buffer[256];
+    snprintf(crc_buffer, sizeof(crc_buffer), "SENDER=0x%x VALUE_ID=%d VALUE=%s VALUE_ID=%d VALUE=%s",
+        sender_hex, value_id_0, value_str_0, value_id_1, value_str_1);
+        
+    // Calculate CRC32 for the received data excluding the CRC field
+    unsigned long computed_crc = calculate_crc32(crc_buffer, strlen(crc_buffer));
+    printk(KERN_INFO "  computed_crc=0x%lX\n", computed_crc);
+
+    // Check CRC32 before transmission
+    if (computed_crc != crc_val) {
+        printk(KERN_ERR "packet_receiver: CRC32 mismatch! Data rejected.\n");
+        return -EIO;
+    }
+
+    // Store the valid packet
+    strcpy(last_valid_packet, crc_buffer);
+    keep_sending = 1;
+
+    printk(KERN_INFO "packet_receiver: Sent data to GPIO %d\n", GPIO_DATA);
+
+    // Return the number of bytes written
+    return len;
+}
+
+// ====================== Device Release ======================
+static int packet_release(struct inode *inode, struct file *file) {
+    printk(KERN_INFO "packet_receiver: Device closed.\n");
+    return 0;
+}
+
+// ====================== Module Init ======================
+static int __init packet_init(void) {
+    int ret;
+
+    // Allocate a device number dynamically
+    ret = alloc_chrdev_region(&dev_number, 0, 1, DEVICE_NAME);
+    if (ret < 0) {
+        printk(KERN_ERR "packet_receiver: Failed to allocate major/minor.\n");
+        return ret;
+    }
+    printk(KERN_INFO "packet_receiver: Registered with major=%d, minor=%d\n",
+           MAJOR(dev_number), MINOR(dev_number));
+
+    // Initialize the cdev structure 
+    cdev_init(&packet_cdev, &fops);
+    packet_cdev.owner = THIS_MODULE;
+
+    // Add the cdev to the kernel 
+    ret = cdev_add(&packet_cdev, dev_number, 1);
+    if (ret < 0) {
+        printk(KERN_ERR "packet_receiver: Unable to add cdev.\n");
+        unregister_chrdev_region(dev_number, 1);
+        return ret;
+    }
+
+    // Create a class for udev 
+    packet_class = class_create(CLASS_NAME);
+    if (IS_ERR(packet_class)) {
+        printk(KERN_ERR "packet_receiver: Failed to create class.\n");
+        cdev_del(&packet_cdev);
+        unregister_chrdev_region(dev_number, 1);
+        return PTR_ERR(packet_class);
+    }
+
+    // Create a device node /dev/packet_receiver
+    if (IS_ERR(device_create(packet_class, NULL, dev_number, NULL, DEVICE_NAME))) {
+        printk(KERN_ERR "packet_receiver: Failed to create device.\n");
+        class_destroy(packet_class);
+        cdev_del(&packet_cdev);
+        unregister_chrdev_region(dev_number, 1);
+        return -1;
+    }
+
+    // Allocate memory for receive buffer
+    recv_buffer = kmalloc(RECV_BUF_SIZE, GFP_KERNEL);
+    if (!recv_buffer) {
+        printk(KERN_ERR "packet_receiver: Failed to allocate recv_buffer.\n");
+        device_destroy(packet_class, dev_number);
+        class_destroy(packet_class);
+        cdev_del(&packet_cdev);
+        unregister_chrdev_region(dev_number, 1);
+        return -ENOMEM;
+    }
+
+    gpio_request(GPIO_DATA, "packet_data");
+    gpio_request(GPIO_CLOCK, "packet_clock");
+    gpio_direction_output(GPIO_DATA, 0);
+    gpio_direction_input(GPIO_CLOCK); // Clock is an input signal
+
+    // Start the transmission thread
+    transmit_thread = kthread_run(transmit_loop, NULL, "packet_transmitter");
+    if (IS_ERR(transmit_thread)) {
+        printk(KERN_ERR "packet_receiver: Failed to create transmit_thread.\n");
+        kfree(recv_buffer);
+        device_destroy(packet_class, dev_number);
+        class_destroy(packet_class);
+        cdev_del(&packet_cdev);
+        unregister_chrdev_region(dev_number, 1);
+        return PTR_ERR(transmit_thread);
+    }
+
+    printk(KERN_INFO "packet_receiver: Module loaded.\n");
+    return 0;
+}
+
+// ====================== Module Exit ======================
+static void __exit packet_exit(void) {
+
+    // Stop the transmission thread
+    kthread_stop(transmit_thread);
+
+    // Free recv_buffer
+    kfree(recv_buffer);
+
+    // Remove device node
+    device_destroy(packet_class, dev_number);
+    // Destroy class
+    class_destroy(packet_class);
+    // Delete cdev
+    cdev_del(&packet_cdev);
+    // Free device numbers
+    unregister_chrdev_region(dev_number, 1);
+    // Free GPIOs
+    gpio_free(GPIO_DATA);
+    gpio_free(GPIO_CLOCK);
+
+    printk(KERN_INFO "packet_receiver: Module unloaded.\n");
+}
+
+module_init(packet_init);
+module_exit(packet_exit);