Create fat16.c

Add implementation for fat16 filesystem

kernel/ata.c

@@ -1,91 +0,0 @@
-#include "ata.h"
-#include "io.h"
-#include "print.h"
-
-#define ATA_TIMEOUT 100000
-
-static inline void ata_delay(void) {
-    /* 400ns delay by reading alternate status */
-    inb(ATA_PRIMARY_CTRL);
-    inb(ATA_PRIMARY_CTRL);
-    inb(ATA_PRIMARY_CTRL);
-    inb(ATA_PRIMARY_CTRL);
-}
-
-static bool ata_wait(uint8_t mask) {
-    for (int i = 0; i < ATA_TIMEOUT; i++) {
-        uint8_t status = inb(ATA_PRIMARY_IO + ATA_REG_STATUS);
-        if (!(status & ATA_SR_BSY) && (status & mask))
-            return true;
-    }
-    return false;
-}
-
-bool ata_init(void) {
-    outb(ATA_PRIMARY_IO + ATA_REG_HDDEVSEL, 0xA0); // master
-    ata_delay();
-
-    outb(ATA_PRIMARY_IO + ATA_REG_COMMAND, ATA_CMD_IDENTIFY);
-    ata_delay();
-
-    uint8_t status = inb(ATA_PRIMARY_IO + ATA_REG_STATUS);
-    if (status == 0)
-        return false; // no drive
-
-    if (!ata_wait(ATA_SR_DRQ))
-        return false;
-
-    uint16_t identify[256];
-    for (int i = 0; i < 256; i++)
-        identify[i] = inw(ATA_PRIMARY_IO);
-
-    print_string("[ATA] Primary master detected\n");
-    return true;
-}
-
-bool ata_read_sector(uint32_t lba, uint8_t* buffer) {
-    if (!buffer) return false;
-
-    outb(ATA_PRIMARY_IO + ATA_REG_HDDEVSEL, 0xE0 | ((lba >> 24) & 0x0F));
-    outb(ATA_PRIMARY_IO + ATA_REG_SECCOUNT0, 1);
-    outb(ATA_PRIMARY_IO + ATA_REG_LBA0, (uint8_t)(lba));
-    outb(ATA_PRIMARY_IO + ATA_REG_LBA1, (uint8_t)(lba >> 8));
-    outb(ATA_PRIMARY_IO + ATA_REG_LBA2, (uint8_t)(lba >> 16));
-    outb(ATA_PRIMARY_IO + ATA_REG_COMMAND, ATA_CMD_READ_PIO);
-
-    if (!ata_wait(ATA_SR_DRQ))
-        return false;
-
-    for (int i = 0; i < 256; i++) {
-        uint16_t data = inw(ATA_PRIMARY_IO);
-        buffer[i * 2]     = data & 0xFF;
-        buffer[i * 2 + 1] = data >> 8;
-    }
-
-    ata_delay();
-    return true;
-}
-
-bool ata_write_sector(uint32_t lba, const uint8_t* buffer) {
-    if (!buffer) return false;
-
-    outb(ATA_PRIMARY_IO + ATA_REG_HDDEVSEL, 0xE0 | ((lba >> 24) & 0x0F));
-    outb(ATA_PRIMARY_IO + ATA_REG_SECCOUNT0, 1);
-    outb(ATA_PRIMARY_IO + ATA_REG_LBA0, (uint8_t)(lba));
-    outb(ATA_PRIMARY_IO + ATA_REG_LBA1, (uint8_t)(lba >> 8));
-    outb(ATA_PRIMARY_IO + ATA_REG_LBA2, (uint8_t)(lba >> 16));
-    outb(ATA_PRIMARY_IO + ATA_REG_COMMAND, ATA_CMD_WRITE_PIO);
-
-    if (!ata_wait(ATA_SR_DRQ))
-        return false;
-
-    for (int i = 0; i < 256; i++) {
-        uint16_t word =
-            buffer[i * 2] |
-            (buffer[i * 2 + 1] << 8);
-        outw(ATA_PRIMARY_IO, word);
-    }
-
-    ata_delay();
-    return true;
-}

kernel/ata.h

@@ -1,43 +0,0 @@
-#ifndef ATA_H
-#define ATA_H
-
-#include <stdint.h>
-#include <stdbool.h>
-
-/* ATA I/O ports */
-#define ATA_PRIMARY_IO     0x1F0
-#define ATA_PRIMARY_CTRL   0x3F6
-
-/* ATA registers */
-#define ATA_REG_DATA       0x00
-#define ATA_REG_ERROR      0x01
-#define ATA_REG_FEATURES   0x01
-#define ATA_REG_SECCOUNT0  0x02
-#define ATA_REG_LBA0       0x03
-#define ATA_REG_LBA1       0x04
-#define ATA_REG_LBA2       0x05
-#define ATA_REG_HDDEVSEL   0x06
-#define ATA_REG_COMMAND    0x07
-#define ATA_REG_STATUS     0x07
-
-/* ATA commands */
-#define ATA_CMD_READ_PIO   0x20
-#define ATA_CMD_WRITE_PIO  0x30
-#define ATA_CMD_IDENTIFY   0xEC
-
-/* Status flags */
-#define ATA_SR_BSY         0x80
-#define ATA_SR_DRDY        0x40
-#define ATA_SR_DRQ         0x08
-#define ATA_SR_ERR         0x01
-
-/* Drive select */
-#define ATA_MASTER         0x00
-#define ATA_SLAVE          0x10
-
-/* Public API */
-bool ata_init(void);
-bool ata_read_sector(uint32_t lba, uint8_t* buffer);
-bool ata_write_sector(uint32_t lba, const uint8_t* buffer);
-
-#endif

kernel/fat16.c

@@ -0,0 +1,107 @@
+#include "fat16.h"
+#include "ata.h"   // Use ata_read_sector and ata_write_sector
+#include "print.h" // For debugging
+#include <string.h> // For string manipulation
+
+// Global variables
+static fat16_boot_sector_t boot_sector;
+static uint32_t root_dir_sector = FAT16_ROOT_DIR_SECTOR;
+
+// Read a sector from the disk using ATA
+bool read_sector(uint32_t lba, uint8_t* buffer) {
+    return ata_read_sector(lba, buffer);
+}
+
+// Write a sector to the disk using ATA
+bool write_sector(uint32_t lba, const uint8_t* buffer) {
+    return ata_write_sector(lba, buffer);
+}
+
+// Parse the boot sector to retrieve basic file system info
+bool parse_fat16_boot_sector(void) {
+    uint8_t sector_buffer[FAT16_SECTOR_SIZE];
+
+    // Read the boot sector
+    if (!read_sector(FAT16_BOOT_SECTOR, sector_buffer)) {
+        print_string("[FAT16] Failed to read boot sector\n");
+        return false;
+    }
+
+    // Cast to boot sector structure
+    memcpy(&boot_sector, sector_buffer, sizeof(fat16_boot_sector_t));
+
+    // Check for FAT16 signature
+    if (boot_sector.oem_name[0] != 'F' || boot_sector.oem_name[1] != 'A' || boot_sector.oem_name[2] != 'T') {
+        print_string("[FAT16] Invalid FAT16 boot sector signature\n");
+        return false;
+    }
+
+    print_string("[FAT16] FAT16 boot sector parsed successfully\n");
+    return true;
+}
+
+// Parse the root directory
+bool parse_fat16_root_dir(void) {
+    uint8_t sector_buffer[FAT16_SECTOR_SIZE];
+
+    for (int i = 0; i < (boot_sector.max_root_entries / (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t))); i++) {
+        // Read root directory sector
+        if (!read_sector(root_dir_sector + i, sector_buffer)) {
+            print_string("[FAT16] Failed to read root directory sector\n");
+            return false;
+        }
+
+        // Parse the root directory entries
+        for (int j = 0; j < (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t)); j++) {
+            fat16_dir_entry_t* entry = (fat16_dir_entry_t*)&sector_buffer[j * sizeof(fat16_dir_entry_t)];
+            if (entry->name[0] == 0x00) {
+                // End of directory entries
+                return true;
+            }
+            if (entry->name[0] != 0xE5) {
+                // Print file name (8.3 format)
+                char filename[12];
+                strncpy(filename, (char*)entry->name, 8);
+                filename[8] = '.';
+                strncpy(&filename[9], (char*)entry->ext, 3);
+                filename[11] = '\0';
+                print_string(filename);
+                print_string("\n");
+            }
+        }
+    }
+    return true;
+}
+
+// Read a specific directory entry from the FAT16 root directory
+bool read_fat16_entry(uint16_t entry_index, fat16_dir_entry_t* entry) {
+    uint8_t sector_buffer[FAT16_SECTOR_SIZE];
+    uint32_t sector_num = FAT16_ROOT_DIR_SECTOR + (entry_index / (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t)));
+    uint16_t entry_offset = entry_index % (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t));
+
+    // Read the sector
+    if (!read_sector(sector_num, sector_buffer)) {
+        print_string("[FAT16] Failed to read root directory sector\n");
+        return false;
+    }
+
+    // Get the entry
+    memcpy(entry, &sector_buffer[entry_offset * sizeof(fat16_dir_entry_t)], sizeof(fat16_dir_entry_t));
+    return true;
+}
+
+// Mount the FAT16 filesystem
+bool mount_fat16(void) {
+    // Parse the boot sector
+    if (!parse_fat16_boot_sector()) {
+        return false;
+    }
+
+    // Parse the root directory
+    if (!parse_fat16_root_dir()) {
+        return false;
+    }
+
+    print_string("[FAT16] Filesystem mounted successfully\n");
+    return true;
+}

kernel/fat16.h

@@ -0,0 +1,60 @@
+#ifndef FAT16_H
+#define FAT16_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+/* FAT16 Constants */
+#define FAT16_SECTOR_SIZE        512
+#define FAT16_CLUSTER_SIZE       1
+#define FAT16_MAX_FILENAME_LEN   11   // 8.3 format
+#define FAT16_ROOT_DIR_ENTRIES   224  // Fat16 root directory entries (typically 512 bytes per entry)
+
+#define FAT16_BOOT_SECTOR        0
+#define FAT16_FAT1_SECTOR        1
+#define FAT16_FAT2_SECTOR        2
+#define FAT16_ROOT_DIR_SECTOR    19  // First sector of root directory
+
+/* Boot Sector */
+typedef struct {
+    uint8_t jmp[3];               // Jump instruction to code
+    uint8_t oem_name[8];          // OEM Name
+    uint16_t bytes_per_sector;    // Bytes per sector (512)
+    uint8_t sectors_per_cluster;  // Sectors per cluster
+    uint16_t reserved_sectors;    // Reserved sectors
+    uint8_t num_fats;             // Number of FAT tables
+    uint16_t max_root_entries;    // Max number of root directory entries
+    uint16_t total_sectors_16;    // Total sectors in FAT16
+    uint8_t media_type;           // Media type (0xF8 = fixed drive)
+    uint16_t sectors_per_fat;    // Sectors per FAT table
+    uint16_t sectors_per_track;  // Sectors per track (for CHS addressing)
+    uint16_t num_heads;          // Number of heads (for CHS addressing)
+    uint32_t hidden_sectors;     // Hidden sectors (before the partition)
+    uint32_t total_sectors_32;   // Total sectors in FAT16 (extended)
+} __attribute__((packed)) fat16_boot_sector_t;
+
+/* FAT16 Directory Entry */
+typedef struct {
+    uint8_t name[8];   // File name (8 chars)
+    uint8_t ext[3];    // File extension (3 chars)
+    uint8_t attributes; // File attributes (e.g., directory, read-only)
+    uint8_t reserved;   // Reserved
+    uint8_t creation_time[2]; // Creation time
+    uint8_t creation_date[2]; // Creation date
+    uint8_t last_access_date[2]; // Last access date
+    uint8_t first_cluster_high[2]; // High part of first cluster number
+    uint8_t last_mod_time[2];  // Last modification time
+    uint8_t last_mod_date[2];  // Last modification date
+    uint8_t first_cluster_low[2];  // Low part of first cluster number
+    uint32_t file_size;         // File size in bytes
+} __attribute__((packed)) fat16_dir_entry_t;
+
+/* Function Prototypes */
+bool mount_fat16(void);
+bool read_sector(uint32_t lba, uint8_t* buffer);
+bool write_sector(uint32_t lba, const uint8_t* buffer);
+bool parse_fat16_boot_sector(void);
+bool parse_fat16_root_dir(void);
+bool read_fat16_entry(uint16_t entry_index, fat16_dir_entry_t* entry);
+
+#endif // FAT16_H