@@ -186,6 +186,9 @@ mov %eax, %fs
   mov %eax, %gs
 
   call load_kernel
+
+  test %eax, %eax
+  jnz loop
   
   # create a page directory for the kernel that maps it to 0xC0000000
   # and identity maps the first 1M of memory

@@ -1,182 +0,0 @@
-#include "fat.h"
-#include "string.h"
-#include <stdint.h>
-
-typedef struct {
-    char jmp[3];
-    char oemname[8];
-
-    uint16_t bytes_per_sect;
-    uint8_t sect_per_cluster;
-    uint16_t num_reserved_sectors;
-    uint8_t num_FAT;
-    uint16_t max_root_dir_entries;
-    uint16_t total_log_sectors;
-    uint8_t media_desc;
-    uint16_t log_sect_per_fat;
-} __attribute__((packed))  BOOT_SECT;
-
-typedef struct {
-    char name[8];
-    char ext[3];
-    uint8_t file_attr;
-    uint8_t user_attr;
-    uint8_t del_char;
-    uint16_t create_time;
-    uint16_t create_date;
-    uint16_t last_access_date;
-    uint16_t access_rights;
-    uint16_t last_modified_time;
-    uint16_t last_modified_date;
-    uint16_t start_of_clusters;
-    uint32_t file_size;
-} __attribute__((packed)) DIR_ENTRY;
-
-typedef struct {
-    uint8_t seq_num;
-    uint16_t part_1[5];
-    uint8_t file_attr;
-    uint8_t user_attr;
-    uint8_t del_char;
-    uint16_t part_2[6];
-    uint16_t start_of_clusters;
-    uint16_t part_3[2];
-} __attribute__((packed)) VFAT_LFN_ENTRY;
-
-
-void *FAT_addr;
-BOOT_SECT *boot_sect;
-
-uint32_t FAT1_lba;
-uint32_t FAT2_lba;
-uint32_t root_lba;
-uint32_t data_lba;
-
-void FAT_init() {
-    // open image file
-    FAT_addr = (void*)(0x10000);
-
-    boot_sect = (BOOT_SECT*)(FAT_addr);
-
-    FAT1_lba = boot_sect->num_reserved_sectors;
-    FAT2_lba = FAT1_lba + boot_sect->log_sect_per_fat;
-    root_lba = FAT1_lba + (boot_sect->log_sect_per_fat * boot_sect->num_FAT);
-
-    long root_dir_size = boot_sect->max_root_dir_entries * sizeof(DIR_ENTRY);
-    data_lba = root_lba + (root_dir_size / boot_sect->bytes_per_sect);
-}
-
-void *FAT_read_sector_offset(uint32_t lba, uint32_t *offset) {
-    if (offset != NULL) {
-        lba += (*offset) / boot_sect->bytes_per_sect;
-        *offset = (*offset) % boot_sect->bytes_per_sect;
-    }
-
-    return (void*)((long)(FAT_addr) + (long)(lba * boot_sect->bytes_per_sect));
-}
-
-void *FAT_read_cluster(uint16_t cluster, void *buffer) {
-    // TODO: perform memcpy
-    void *addr = FAT_read_sector_offset(data_lba + ((cluster - 2) * boot_sect->sect_per_cluster), NULL);
-
-    uint32_t cluster_size = boot_sect->bytes_per_sect * boot_sect->sect_per_cluster;
-
-    memcpy(buffer, addr, cluster_size);
-
-    return (void*)((uint8_t*)(buffer) + cluster_size);
-}
-
-int FAT_root_dir_next(int index, char *fname_buffer, uint16_t *first_cluster, uint32_t *file_size) {
-    memset(fname_buffer, 0, sizeof(fname_buffer));
-
-    while (1) {
-        // index overflow
-        if (index >= boot_sect->max_root_dir_entries) {
-            return -1;
-        }
-
-        uint32_t offset = index * sizeof(DIR_ENTRY);
-        void *sect = FAT_read_sector_offset(root_lba, &offset);
-        DIR_ENTRY *dir_entry = (DIR_ENTRY *)((uint32_t)(sect) + offset);
-
-        // if first character of name is 0, then no subsequent entry is in use
-        if (dir_entry->name[0] == 0x00) { 
-            return -1; 
-        }
-
-        // deleted file
-        if (dir_entry->name[0] == (char)(0xE5)) {
-            index++;
-            continue;
-        }
-
-        // VFAT LFN entry
-        if (dir_entry->file_attr == 0x0F && dir_entry->start_of_clusters == 0 && dir_entry->file_size != 0) {
-            VFAT_LFN_ENTRY *lfn_entry = (VFAT_LFN_ENTRY*)(dir_entry);
-
-            int offset = 13 * ((lfn_entry->seq_num & 0x3F) - 1);
-
-            // read long file name
-            for (int i = 0; i < 5; i++) {
-                fname_buffer[offset++] = lfn_entry->part_1[i];
-            }
-
-            for (int i = 0; i < 6; i++) {
-                fname_buffer[offset++] = lfn_entry->part_2[i];
-            }
-
-            for (int i = 0; i < 2; i++) {
-                fname_buffer[offset++] = lfn_entry->part_3[i];
-            }
-
-            index++;
-            continue;
-        }
-
-        if (index == 0 && (dir_entry->file_attr & 0x08) && dir_entry->file_size == 0) {
-        // volume label
-
-        } else if ((dir_entry->file_attr & 0x10) && dir_entry->file_size == 0) {
-        // subdirectory
-
-        } else {
-        // regular file
-
-        }
-
-        *file_size = dir_entry->file_size;
-        *first_cluster = dir_entry->start_of_clusters;
-
-        // if no VFAT LFN exists, use DOS name
-        if (fname_buffer[0] == 0) {
-            for (int i = 0; i < 8; i++) {
-                fname_buffer[i] = dir_entry->name[i];
-            }
-            fname_buffer[8] = '.';
-            for (int i = 0; i < 3; i++) {
-                fname_buffer[i + 9] = dir_entry->ext[i];
-            }
-            fname_buffer[12] = 0;
-        }
-
-        return index + 1;
-    }
-}
-
-uint16_t FAT_next_cluster(uint16_t cluster) {
-    // assuming FAT12
-    uint32_t offset = (cluster >> 1) * 3;
-    uint8_t *sect = FAT_read_sector_offset(FAT1_lba, &offset);
-    sect += offset;
-
-    if (cluster & 0x01) {
-        uint16_t high = (uint16_t)(sect[2]);
-        uint16_t low = (uint16_t)(sect[1] & 0xF0) >> 4;
-        return (high << 4) | low;
-    } else {
-        uint16_t low = (uint16_t)(sect[0]);
-        uint16_t high = (uint16_t)(sect[1] & 0x0F) << 8;
-        return low | high;
-    }
-}
-

@@ -1,13 +0,0 @@
-#ifndef FAT_H
-#define FAT_H
-
-#include <stdint.h>
-
-void FAT_init();
-void *FAT_read_sector_offset(uint32_t lba, uint32_t *offset);
-void *FAT_read_cluster(uint16_t cluster, void *buffer);
-uint16_t FAT_next_cluster(uint16_t cluster);
-int FAT_root_dir_next(int index, char *fname_buffer, uint16_t *first_cluster, uint32_t *file_size);
-void *FAT_find_file(const char *fname);
-
-#endif

@@ -1,7 +1,8 @@
 #include <stdint.h>
+#include <stddef.h>
 
 #include "string.h"
-#include "fat.h"
+#include "fat12.h"
 
 void printc(char c) {
     static uint8_t *display = (uint8_t*)(0xB8000);
@@ -21,6 +22,23 @@
     while (1) {}
 }
 
+FAT12_descriptor_t fat_desc;
+
+void *FAT12_read(uint32_t lba, uint32_t *offset, size_t size, void *buffer) {
+    void *FAT_addr = (void*)(0x10000);
+
+    if (offset != NULL) {
+        lba += (*offset) / fat_desc.bytes_per_sect;
+        *offset = (*offset) % fat_desc.bytes_per_sect;
+
+        void *ptr = (void*)((long)(FAT_addr) + (long)(lba * fat_desc.bytes_per_sect));
+        return memcpy(buffer, ptr + *offset, size);
+    } else {
+        void *ptr = (void*)((long)(FAT_addr) + (long)(lba * fat_desc.bytes_per_sect));
+        return memcpy(buffer, ptr, size);
+    }
+}
+
 int load_kernel() {
     // debug output
     uint8_t *dbuf = (uint8_t *)(0x10000);
@@ -37,8 +55,7 @@ printc(' ');
     }
 
     //while (1);
-
-    FAT_init();
+    FAT12_init(&fat_desc);
 
     int i = 0;
 
@@ -49,7 +66,7 @@ while (1) {
         char buffer[832];
         uint32_t file_size;
 
-        i = FAT_root_dir_next(i, buffer, &first_cluster, &file_size);
+        i = FAT12_root_dir_next(&fat_desc, i, buffer, &first_cluster, &file_size);
 
         print_string(buffer);
         print_string("  ");
@@ -62,8 +79,8 @@ // copy all clusters
     uint16_t cluster = first_cluster;
     uint8_t *buffer = (uint8_t *)(0x100000);
     while (1) {
-        buffer = FAT_read_cluster(cluster, buffer);
-        cluster = FAT_next_cluster(cluster);
+        buffer = FAT12_read_cluster(&fat_desc, cluster, buffer);
+        cluster = FAT12_next_cluster(&fat_desc, cluster);
         
         if (cluster == 0xFFF || cluster == 0x000) { break; }
     }

@@ -1,7 +1,6 @@
 #include "paging.h"
 #include "linker.h"
 #include "string.h"
-#include "fat.h"
 
 
 void *create_kernel_environment() {

@@ -0,0 +1,180 @@
+#include "fat12.h"
+
+#include <stdint.h>
+#include <stddef.h>
+
+#include "string.h"
+
+typedef struct {
+    char jmp[3];
+    char oemname[8];
+
+    uint16_t bytes_per_sect;
+    uint8_t sect_per_cluster;
+    uint16_t num_reserved_sectors;
+    uint8_t num_FAT;
+    uint16_t max_root_dir_entries;
+    uint16_t total_log_sectors;
+    uint8_t media_desc;
+    uint16_t log_sect_per_fat;
+} __attribute__((packed))  BOOT_SECT;
+
+typedef struct {
+    char name[8];
+    char ext[3];
+    uint8_t file_attr;
+    uint8_t user_attr;
+    uint8_t del_char;
+    uint16_t create_time;
+    uint16_t create_date;
+    uint16_t last_access_date;
+    uint16_t access_rights;
+    uint16_t last_modified_time;
+    uint16_t last_modified_date;
+    uint16_t start_of_clusters;
+    uint32_t file_size;
+} __attribute__((packed)) DIR_ENTRY;
+
+typedef struct {
+    uint8_t seq_num;
+    uint16_t part_1[5];
+    uint8_t file_attr;
+    uint8_t user_attr;
+    uint8_t del_char;
+    uint16_t part_2[6];
+    uint16_t start_of_clusters;
+    uint16_t part_3[2];
+} __attribute__((packed)) VFAT_LFN_ENTRY;
+
+
+/**
+ * @brief 
+*/
+void FAT12_init(FAT12_descriptor_t *fat) {
+    BOOT_SECT boot_sect;
+    FAT12_read(0, NULL, sizeof(boot_sect), &boot_sect);
+
+    // copy FAT parameters from boot sector into fat descriptor
+    fat->bytes_per_sect         = boot_sect.bytes_per_sect;
+    fat->log_sect_per_fat       = boot_sect.log_sect_per_fat;
+    fat->max_root_dir_entries   = boot_sect.max_root_dir_entries;
+    fat->media_desc             = boot_sect.media_desc;
+    fat->num_FAT                = boot_sect.num_FAT;
+    fat->num_reserved_sectors   = boot_sect.num_reserved_sectors;
+    fat->sect_per_cluster       = boot_sect.sect_per_cluster;
+    fat->total_log_sectors      = boot_sect.total_log_sectors;
+
+    // calculate starting addresses of FAT regions
+    fat->FAT1_lba = fat->num_reserved_sectors;
+    fat->FAT2_lba = fat->FAT1_lba + fat->log_sect_per_fat;
+    fat->root_lba = fat->FAT1_lba + (fat->log_sect_per_fat * fat->num_FAT);
+
+    long root_dir_size = fat->max_root_dir_entries * sizeof(DIR_ENTRY);
+    fat->data_lba = fat->root_lba + (root_dir_size / fat->bytes_per_sect);
+    
+    // calculate cluster size
+    fat->cluster_size = fat->bytes_per_sect * fat->sect_per_cluster;
+}
+
+void *FAT12_read_cluster(FAT12_descriptor_t *fat, uint16_t cluster, void *buffer) {
+    FAT12_read(fat->data_lba + ((cluster - 2) * fat->sect_per_cluster), NULL, fat->cluster_size, buffer);
+
+    return buffer += fat->cluster_size;
+}
+
+int FAT12_root_dir_next(FAT12_descriptor_t *fat, int index, char *fname_buffer, uint16_t *first_cluster, uint32_t *file_size) {
+    memset(fname_buffer, 0, sizeof(fname_buffer));
+
+    while (1) {
+        //printk("%i\n", index);
+        // index overflow
+        if (index >= fat->max_root_dir_entries) {
+            return -1;
+        }
+
+        uint32_t offset = index * sizeof(DIR_ENTRY);
+        DIR_ENTRY dir_entry;
+        FAT12_read(fat->root_lba, &offset, sizeof(DIR_ENTRY), &dir_entry);
+
+        // if first character of name is 0, then no subsequent entry is in use
+        if (dir_entry.name[0] == 0x00) { 
+            return -1; 
+        }
+
+        // deleted file
+        if (dir_entry.name[0] == (char)(0xE5)) {
+            index++;
+            continue;
+        }
+
+        // VFAT LFN entry
+        if (dir_entry.file_attr == 0x0F && dir_entry.start_of_clusters == 0 && dir_entry.file_size != 0) {
+            VFAT_LFN_ENTRY *lfn_entry = (VFAT_LFN_ENTRY*)(&dir_entry);
+
+            int offset = 13 * ((lfn_entry->seq_num & 0x3F) - 1);
+
+            // read long file name
+            for (int i = 0; i < 5; i++) {
+                fname_buffer[offset++] = lfn_entry->part_1[i];
+            }
+
+            for (int i = 0; i < 6; i++) {
+                fname_buffer[offset++] = lfn_entry->part_2[i];
+            }
+
+            for (int i = 0; i < 2; i++) {
+                fname_buffer[offset++] = lfn_entry->part_3[i];
+            }
+
+            index++;
+            continue;
+        }
+
+        if (index == 0 && (dir_entry.file_attr & 0x08) && dir_entry.file_size == 0) {
+            // volume label
+            index++;
+            continue;
+
+        } else if ((dir_entry.file_attr & 0x10) && dir_entry.file_size == 0) {
+        // subdirectory
+
+        } else {
+        // regular file
+
+        }
+
+        *file_size = dir_entry.file_size;
+        *first_cluster = dir_entry.start_of_clusters;
+
+        // if no VFAT LFN exists, use DOS name
+        if (fname_buffer[0] == 0) {
+            for (int i = 0; i < 8; i++) {
+                fname_buffer[i] = dir_entry.name[i];
+            }
+            fname_buffer[8] = '.';
+            for (int i = 0; i < 3; i++) {
+                fname_buffer[i + 9] = dir_entry.ext[i];
+            }
+            fname_buffer[12] = 0;
+        }
+
+        return index + 1;
+    }
+}
+
+uint16_t FAT12_next_cluster(FAT12_descriptor_t *fat, uint16_t cluster) {
+    // assuming FAT12
+    uint32_t offset = (cluster >> 1) * 3;
+    uint8_t sect[3];
+    FAT12_read(fat->FAT1_lba, &offset, sizeof(sect), sect);
+
+    if (cluster & 0x01) {
+        uint16_t high = (uint16_t)(sect[2]);
+        uint16_t low = (uint16_t)(sect[1] & 0xF0) >> 4;
+        return (high << 4) | low;
+    } else {
+        uint16_t low = (uint16_t)(sect[0]);
+        uint16_t high = (uint16_t)(sect[1] & 0x0F) << 8;
+        return low | high;
+    }
+}

@@ -0,0 +1,82 @@
+#ifndef FAT12_H
+#define FAT12_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+typedef struct {
+    // logical block addresses of FAT regions
+    uint32_t FAT1_lba;
+    uint32_t FAT2_lba;
+    uint32_t root_lba;
+    uint32_t data_lba;
+
+    // FAT parameters, read out from boot sector
+    uint32_t bytes_per_sect;
+    uint32_t sect_per_cluster;
+    uint32_t num_reserved_sectors;
+    uint32_t num_FAT;
+    uint32_t max_root_dir_entries;
+    uint32_t total_log_sectors;
+    uint32_t media_desc;
+    uint32_t log_sect_per_fat;
+
+    // calculated cluster size in bytes
+    uint32_t cluster_size;
+} FAT12_descriptor_t;
+
+
+/**
+ * @brief Read out a portion from the raw FAT12 image.
+ * This function has to be defined by whichever code is including this driver.
+ */
+extern void *FAT12_read(uint32_t lba, uint32_t *offset, size_t size, void *buffer);
+
+
+/**
+ * @brief Initialize FAT12 descriptor structure
+ * 
+ * The FAT12 descriptor contains read-out and pre-computed
+ * information about a given FAT12 image or disk.
+ * FAT12_init initializes the descriptor \p fat based on the FAT
+ * device that is accessible through the FAT12_read function.
+ * 
+ * @param fat FAT descriptor to be initialized.
+*/
+void FAT12_init(FAT12_descriptor_t *fat);
+
+/**
+ * @brief Read a single cluster from the FAT image.
+ * 
+ * @param fat FAT descriptor of the FAT device. The driver user has to
+ * ensure that the descriptor corresponds to the FAT device accessible
+ * through the FAT12_read function.
+ * @param cluster Index of the cluster to read.
+ * @param buffer Pointer to a cluster-sized buffer.
+*/
+void *FAT12_read_cluster(FAT12_descriptor_t *fat, uint16_t cluster, void *buffer);
+
+/**
+ * @brief Iterate through entries in the root directory and return the next file name, the first cluster index, and file size.
+ * 
+ * @param fat FAT descriptor of the FAT device.
+ * @param index Index within the root directory table at which to start.
+ * @param fname_buffer Pointer to a buffer for the file name.
+ * @param first_cluster Pointer to a uint16_t to be filled with the index of the first cluster of the file.
+ * @param file_size Pointer to a uint32_t to be filled with the file size.
+ * 
+ * @return -1 if the search has reached an end; Index within the directory table otherwise.
+*/
+int FAT12_root_dir_next(FAT12_descriptor_t *fat, int index, char *fname_buffer, uint16_t *first_cluster, uint32_t *file_size);
+
+/**
+ * @brief Given a cluster index, return the value of the FAT table.
+ * 
+ * @param fat FAT descriptor of the FAT device.
+ * @param cluster Cluster index.
+ *
+ * @return Value of the FAT at the given cluster index.
+*/
+uint16_t FAT12_next_cluster(FAT12_descriptor_t *fat, uint16_t cluster);
+
+#endif

@@ -5,6 +5,7 @@ #include "assert.h"
 #include "core.h"
 
 #include "memory.h"
+#include "fat12.h"
 
 #include <stdint.h>
 
@@ -18,198 +19,41 @@ FAT_lseek,      /* lseek */
     FAT_tell        /* tell */
 };
 
-typedef struct {
-    char jmp[3];
-    char oemname[8];
-
-    uint16_t bytes_per_sect;
-    uint8_t sect_per_cluster;
-    uint16_t num_reserved_sectors;
-    uint8_t num_FAT;
-    uint16_t max_root_dir_entries;
-    uint16_t total_log_sectors;
-    uint8_t media_desc;
-    uint16_t log_sect_per_fat;
-} __attribute__((packed))  BOOT_SECT;
-
-typedef struct {
-    char name[8];
-    char ext[3];
-    uint8_t file_attr;
-    uint8_t user_attr;
-    uint8_t del_char;
-    uint16_t create_time;
-    uint16_t create_date;
-    uint16_t last_access_date;
-    uint16_t access_rights;
-    uint16_t last_modified_time;
-    uint16_t last_modified_date;
-    uint16_t start_of_clusters;
-    uint32_t file_size;
-} __attribute__((packed)) DIR_ENTRY;
-
-typedef struct {
-    uint8_t seq_num;
-    uint16_t part_1[5];
-    uint8_t file_attr;
-    uint8_t user_attr;
-    uint8_t del_char;
-    uint16_t part_2[6];
-    uint16_t start_of_clusters;
-    uint16_t part_3[2];
-} __attribute__((packed)) VFAT_LFN_ENTRY;
-
-
-void *FAT_addr;
-BOOT_SECT *boot_sect;
-
-uint32_t FAT1_lba;
-uint32_t FAT2_lba;
-uint32_t root_lba;
-uint32_t data_lba;
-
 uint8_t *cluster_buffer;
-uint32_t cluster_size;
 
-void FAT_init() {
-    // open image file
-    FAT_addr = (void*)(0x10000);
+FAT12_descriptor_t *fat_desc;
 
-    boot_sect = (BOOT_SECT*)(FAT_addr);
+void *FAT12_read(uint32_t lba, uint32_t *offset, size_t size, void *buffer) {
+    void *FAT_addr = (void*)(0x10000);
 
-    FAT1_lba = boot_sect->num_reserved_sectors;
-    FAT2_lba = FAT1_lba + boot_sect->log_sect_per_fat;
-    root_lba = FAT1_lba + (boot_sect->log_sect_per_fat * boot_sect->num_FAT);
-
-    long root_dir_size = boot_sect->max_root_dir_entries * sizeof(DIR_ENTRY);
-    data_lba = root_lba + (root_dir_size / boot_sect->bytes_per_sect);
-    
-    cluster_size = boot_sect->bytes_per_sect * boot_sect->sect_per_cluster;
-    cluster_buffer = malloc(cluster_size);
-}
+    if (offset != NULL) {
+        lba += (*offset) / fat_desc->bytes_per_sect;
+        *offset = (*offset) % fat_desc->bytes_per_sect;
 
-void *FAT_read_sector_offset(uint32_t lba, uint32_t *offset) {
-    if (offset != NULL) {
-        lba += (*offset) / boot_sect->bytes_per_sect;
-        *offset = (*offset) % boot_sect->bytes_per_sect;
+        void *ptr = (void*)((long)(FAT_addr) + (long)(lba * fat_desc->bytes_per_sect));
+        return memcpy(buffer, ptr + *offset, size);
+    } else {
+        void *ptr = (void*)((long)(FAT_addr) + (long)(lba * fat_desc->bytes_per_sect));
+        return memcpy(buffer, ptr, size);
     }
-
-    return (void*)((long)(FAT_addr) + (long)(lba * boot_sect->bytes_per_sect));
 }
 
-void *FAT_read_cluster(uint16_t cluster, void *buffer) {
-    // TODO: perform memcpy
-    void *addr = FAT_read_sector_offset(data_lba + ((cluster - 2) * boot_sect->sect_per_cluster), NULL);
 
-    uint32_t cluster_size = boot_sect->bytes_per_sect * boot_sect->sect_per_cluster;
+void FAT_init() {
+    fat_desc = malloc(sizeof(FAT12_descriptor_t));
 
-    memcpy(buffer, addr, cluster_size);
+    FAT12_init(fat_desc);
 
-    return (void*)((uint8_t*)(buffer) + cluster_size);
+    cluster_buffer = malloc(fat_desc->cluster_size);
 }
 
-int FAT_root_dir_next(int index, char *fname_buffer, uint16_t *first_cluster, uint32_t *file_size) {
-    //memset(fname_buffer, 0, sizeof(fname_buffer));
-
-    while (1) {
-        // index overflow
-        if (index >= boot_sect->max_root_dir_entries) {
-            return -1;
-        }
-
-        uint32_t offset = index * sizeof(DIR_ENTRY);
-        void *sect = FAT_read_sector_offset(root_lba, &offset);
-        DIR_ENTRY *dir_entry = (DIR_ENTRY *)((uint32_t)(sect) + offset);
-
-        // if first character of name is 0, then no subsequent entry is in use
-        if (dir_entry->name[0] == 0x00) { 
-            return -1; 
-        }
-
-        // deleted file
-        if (dir_entry->name[0] == (char)(0xE5)) {
-            index++;
-            continue;
-        }
-
-        // VFAT LFN entry
-        if (dir_entry->file_attr == 0x0F && dir_entry->start_of_clusters == 0 && dir_entry->file_size != 0) {
-            VFAT_LFN_ENTRY *lfn_entry = (VFAT_LFN_ENTRY*)(dir_entry);
-
-            int offset = 13 * ((lfn_entry->seq_num & 0x3F) - 1);
-
-            // read long file name
-            for (int i = 0; i < 5; i++) {
-                fname_buffer[offset++] = lfn_entry->part_1[i];
-            }
-
-            for (int i = 0; i < 6; i++) {
-                fname_buffer[offset++] = lfn_entry->part_2[i];
-            }
-
-            for (int i = 0; i < 2; i++) {
-                fname_buffer[offset++] = lfn_entry->part_3[i];
-            }
-
-            index++;
-            continue;
-        }
-
-        if (index == 0 && (dir_entry->file_attr & 0x08) && dir_entry->file_size == 0) {
-            // volume label
-            index++;
-            continue;
-
-        } else if ((dir_entry->file_attr & 0x10) && dir_entry->file_size == 0) {
-        // subdirectory
-
-        } else {
-        // regular file
-
-        }
-
-        *file_size = dir_entry->file_size;
-        *first_cluster = dir_entry->start_of_clusters;
-
-        // if no VFAT LFN exists, use DOS name
-        if (fname_buffer[0] == 0) {
-            for (int i = 0; i < 8; i++) {
-                fname_buffer[i] = dir_entry->name[i];
-            }
-            fname_buffer[8] = '.';
-            for (int i = 0; i < 3; i++) {
-                fname_buffer[i + 9] = dir_entry->ext[i];
-            }
-            fname_buffer[12] = 0;
-        }
-
-        return index + 1;
-    }
-}
 
 int FAT_dir_next(file_t *file, int index, char *fname_buffer) {
     uint16_t first_cluster;
     uint32_t file_size;
 
     // TODO: subdirectories
-    return FAT_root_dir_next(index, fname_buffer, &first_cluster, &file_size);
-}
-
-uint16_t FAT_next_cluster(uint16_t cluster) {
-    // assuming FAT12
-    uint32_t *offset = (cluster >> 1) * 3;
-    uint8_t *sect = FAT_read_sector_offset(FAT1_lba, &offset);
-    sect += (uint32_t)(offset);
-
-    if (cluster & 0x01) {
-        uint16_t high = (uint16_t)(sect[2]);
-        uint16_t low = (uint16_t)(sect[1] & 0xF0) >> 4;
-        return (high << 4) | low;
-    } else {
-        uint16_t low = (uint16_t)(sect[0]);
-        uint16_t high = (uint16_t)(sect[1] & 0x0F) << 8;
-        return low | high;
-    }
+    return FAT12_root_dir_next(fat_desc, index, fname_buffer, &first_cluster, &file_size);
 }
 
 int FAT_openat(file_t *root, file_t *handle, const char *fname, int flags) {
@@ -221,7 +65,7 @@ while (1) {
         char buffer[832];
         uint32_t file_size;
 
-        i = FAT_root_dir_next(i, buffer, &first_cluster, &file_size);
+        i = FAT12_root_dir_next(fat_desc, i, buffer, &first_cluster, &file_size);
         if (i <= 0) { return -1; }
 
         if (strcmp(buffer, fname) == 0) {
@@ -245,22 +89,22 @@ if (offset + count > file_size) {
         count = file_size - offset;
     }
 
-    while (offset >= cluster_size) {
-        cluster = FAT_next_cluster(cluster);
+    while (offset >= fat_desc->cluster_size) {
+        cluster = FAT12_next_cluster(fat_desc, cluster);
         if (cluster == 0xFFF || cluster == 0x000) { return -1; }
-        offset -= cluster_size;
+        offset -= fat_desc->cluster_size;
     }
 
     while (count > 0) {
         if (cluster == 0xFFF || cluster == 0x000) { break; }
 
-        FAT_read_cluster(cluster, cluster_buffer);
-        cluster = FAT_next_cluster(cluster);
+        FAT12_read_cluster(fat_desc, cluster, cluster_buffer);
+        cluster = FAT12_next_cluster(fat_desc, cluster);
 
         uint32_t memcpy_size;
 
-        if (offset + count > cluster_size) {
-            memcpy_size = (cluster_size - offset);
+        if (offset + count > fat_desc->cluster_size) {
+            memcpy_size = (fat_desc->cluster_size - offset);
         } else {
             memcpy_size = count;
         }