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const_mbr: Initialize MBR at compile-time
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This saves VFS_SECTOR_SIZE (512) bytes of RAM
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@mbrossard
mbrossard committed Jan 1, 2022
1 parent c49da21 commit 844b7cd
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Showing 3 changed files with 50 additions and 47 deletions.
2 changes: 1 addition & 1 deletion source/daplink/drag-n-drop/vfs_user.c
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Original file line number Diff line number Diff line change
Expand Up @@ -130,7 +130,7 @@ void vfs_user_build_filesystem()
uint32_t file_size;
vfs_file_t file_handle;
// Setup the filesystem based on target parameters
vfs_init(get_daplink_drive_name(), VFS_DISK_SIZE);
vfs_init(get_daplink_drive_name());
// MBED.HTM
file_size = get_file_size(read_file_mbed_htm);
vfs_create_file(get_daplink_url_name(), read_file_mbed_htm, 0, file_size);
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89 changes: 46 additions & 43 deletions source/daplink/drag-n-drop/virtual_fs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -120,27 +120,54 @@ static bool filename_character_valid(char character);
COMPILER_ASSERT(0x0200 == VFS_SECTOR_SIZE);
// If root directory size changes update max_root_dir_entries
COMPILER_ASSERT(0x0020 == sizeof(root_dir_t) / sizeof(FatDirectoryEntry_t));
static const mbr_t mbr_tmpl = {

#define MBR_BYTES_PER_SECTOR 0x0200
#define MBR_SECTORS_PER_CLUSTER 0x08
#define TOTAL_SECTORS ((VFS_DISK_SIZE + KB(64)) / MBR_BYTES_PER_SECTOR)
#if (TOTAL_SECTORS < (FAT_CLUSTERS_MIN * MBR_SECTORS_PER_CLUSTER))
// #warning "MBR Total Sector resulting in smaller number of FAT clusters than expected"
#define MBR_TOTAL_SECTORS (FAT_CLUSTERS_MIN * MBR_SECTORS_PER_CLUSTER)
#elif (TOTAL_SECTORS > (FAT_CLUSTERS_MAX * MBR_SECTORS_PER_CLUSTER))
// #warning "MBR Total Sector resulting in larger number of FAT clusters than expected"
#define MBR_TOTAL_SECTORS (FAT_CLUSTERS_MAX * MBR_SECTORS_PER_CLUSTER)
#else
#define MBR_TOTAL_SECTORS TOTAL_SECTORS
#endif

#if (MBR_TOTAL_SECTORS >= 0x10000)
#define MBR_TOTAL_LOGICAL_SECTORS 0
#define MBR_BIG_SECTORS_ON_DRIVE MBR_TOTAL_SECTORS
#else
#define MBR_TOTAL_LOGICAL_SECTORS MBR_TOTAL_SECTORS
#define MBR_BIG_SECTORS_ON_DRIVE 0
#endif

// FAT table will likely be larger than needed, but this is allowed by the
// fat specification
#define MBR_NUMBER_OF_CLUSTERS (MBR_TOTAL_SECTORS / MBR_SECTORS_PER_CLUSTER)
#define MBR_LOGICAL_SECTORS_PER_FAT ((MBR_NUMBER_OF_CLUSTERS * 2 + VFS_SECTOR_SIZE - 1) / VFS_SECTOR_SIZE)

const mbr_t mbr = {
/*uint8_t[11]*/.boot_sector = {
0xEB, 0x3C, 0x90,
'M', 'S', 'D', '0', 'S', '4', '.', '1' // OEM Name in text (8 chars max)
},
/*uint16_t*/.bytes_per_sector = 0x0200, // 512 bytes per sector
/*uint8_t */.sectors_per_cluster = 0x08, // 4k cluser
/*uint16_t*/.reserved_logical_sectors = 0x0001, // mbr is 1 sector
/*uint8_t */.num_fats = 0x02, // 2 FATs
/*uint16_t*/.max_root_dir_entries = 0x0020, // 32 dir entries (max)
/*uint16_t*/.total_logical_sectors = 0x1f50, // sector size * # of sectors = drive size
/*uint8_t */.media_descriptor = 0xf8, // fixed disc = F8, removable = F0
/*uint16_t*/.logical_sectors_per_fat = 0x0001, // FAT is 1k - ToDO:need to edit this
/*uint16_t*/.physical_sectors_per_track = 0x0001, // flat
/*uint16_t*/.heads = 0x0001, // flat
/*uint32_t*/.hidden_sectors = 0x00000000, // before mbt, 0
/*uint32_t*/.big_sectors_on_drive = 0x00000000, // 4k sector. not using large clusters
/*uint16_t*/.bytes_per_sector = MBR_BYTES_PER_SECTOR, // 512 bytes per sector
/*uint8_t */.sectors_per_cluster = MBR_SECTORS_PER_CLUSTER, // 4k cluser
/*uint16_t*/.reserved_logical_sectors = 0x0001, // mbr is 1 sector
/*uint8_t */.num_fats = 0x02, // 2 FATs
/*uint16_t*/.max_root_dir_entries = 0x0020, // 32 dir entries (max)
/*uint16_t*/.total_logical_sectors = MBR_TOTAL_LOGICAL_SECTORS, // sector size * # of sectors = drive size
/*uint8_t */.media_descriptor = 0xf8, // fixed disc = F8, removable = F0
/*uint16_t*/.logical_sectors_per_fat = MBR_LOGICAL_SECTORS_PER_FAT, // FAT is 1k - ToDO:need to edit this
/*uint16_t*/.physical_sectors_per_track = 0x0001, // flat
/*uint16_t*/.heads = 0x0001, // flat
/*uint32_t*/.hidden_sectors = 0x00000000, // before mbt, 0
/*uint32_t*/.big_sectors_on_drive = MBR_BIG_SECTORS_ON_DRIVE, // 4k sector. not using large clusters
/*uint8_t */.physical_drive_number = 0x00,
/*uint8_t */.not_used = 0x00, // Current head. Linux tries to set this to 0x1
/*uint8_t */.boot_record_signature = 0x29, // signature is present
/*uint32_t*/.volume_id = 0x27021974, // serial number
/*uint8_t */.not_used = 0x00, // Current head. Linux tries to set this to 0x1
/*uint8_t */.boot_record_signature = 0x29, // signature is present
/*uint32_t*/.volume_id = 0x27021974, // serial number
// needs to match the root dir label
/*char[11]*/.volume_label = {'D', 'A', 'P', 'L', 'I', 'N', 'K', '-', 'D', 'N', 'D'},
// unused by msft - just a label (FAT, FAT12, FAT16)
Expand Down Expand Up @@ -287,7 +314,6 @@ static const FatDirectoryEntry_t dir_entry_tmpl = {
/*uint32_t*/ .filesize = 0x00000000
};

mbr_t mbr;
file_allocation_table_t fat;
virtual_media_t virtual_media[16];
root_dir_t dir_current;
Expand Down Expand Up @@ -318,13 +344,11 @@ static void write_fat(file_allocation_table_t *fat, uint32_t idx, uint16_t val)
fat->f[high_idx] = (val >> 8) & 0xFF;
}

void vfs_init(const vfs_filename_t drive_name, uint32_t disk_size)
void vfs_init(const vfs_filename_t drive_name)
{
uint32_t i;
uint32_t num_clusters;
uint32_t total_sectors;

// Clear everything
memset(&mbr, 0, sizeof(mbr));
memset(&fat, 0, sizeof(fat));
fat_idx = 0;
memset(&virtual_media, 0, sizeof(virtual_media));
Expand All @@ -334,28 +358,7 @@ void vfs_init(const vfs_filename_t drive_name, uint32_t disk_size)
file_change_cb = file_change_cb_stub;
virtual_media_idx = 0;
data_start = 0;
// Initialize MBR
memcpy(&mbr, &mbr_tmpl, sizeof(mbr_t));
total_sectors = ((disk_size + KB(64)) / mbr.bytes_per_sector);
// Make sure this is the right size for a FAT16 volume
if (total_sectors < FAT_CLUSTERS_MIN * mbr.sectors_per_cluster) {
util_assert(0);
total_sectors = FAT_CLUSTERS_MIN * mbr.sectors_per_cluster;
} else if (total_sectors > FAT_CLUSTERS_MAX * mbr.sectors_per_cluster) {
util_assert(0);
total_sectors = FAT_CLUSTERS_MAX * mbr.sectors_per_cluster;
}
if (total_sectors >= 0x10000) {
mbr.total_logical_sectors = 0;
mbr.big_sectors_on_drive = total_sectors;
} else {
mbr.total_logical_sectors = total_sectors;
mbr.big_sectors_on_drive = 0;
}
// FAT table will likely be larger than needed, but this is allowed by the
// fat specification
num_clusters = total_sectors / mbr.sectors_per_cluster;
mbr.logical_sectors_per_fat = (num_clusters * 2 + VFS_SECTOR_SIZE - 1) / VFS_SECTOR_SIZE;

// Initailize virtual media
memcpy(&virtual_media, &virtual_media_tmpl, sizeof(virtual_media_tmpl));
virtual_media[MEDIA_IDX_FAT1].length = VFS_SECTOR_SIZE * mbr.logical_sectors_per_fat;
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6 changes: 3 additions & 3 deletions source/daplink/drag-n-drop/virtual_fs.h
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@
#define VIRTUAL_FS_H

#include <stdint.h>
#include <stdbool.h>
#include <stdbool.h>

#ifdef __cplusplus
extern "C" {
Expand Down Expand Up @@ -68,8 +68,8 @@ typedef uint32_t (*vfs_read_cb_t)(uint32_t sector_offset, uint8_t *data, uint32_
typedef void (*vfs_file_change_cb_t)(const vfs_filename_t filename, vfs_file_change_t change,
vfs_file_t file, vfs_file_t new_file_data);

// Initialize the filesystem with the given size and name
void vfs_init(const vfs_filename_t drive_name, uint32_t disk_size);
// Initialize the filesystem with the given name
void vfs_init(const vfs_filename_t drive_name);

// Get the total size of the virtual filesystem
uint32_t vfs_get_total_size(void);
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