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Statically ensure valid FAT16 cluster count

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Henry Gabryjelski committed 2020-05-28 22:58:59 -07:00
1 parent 2c9826acd9
commit 041defeb63
1 file changed
+13 -2
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src/usb/uf2/ghostfat.c
+13 -2
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@@ -68,8 +68,8 @@ struct TextFile {
#define BPB_RESERVED_SECTORS ( 1)
#define BPB_NUMBER_OF_FATS ( 2)
#define BPB_ROOT_DIR_ENTRIES ( 64)
// Static assertions ensure CFG_UF2_NUM_BLOCKS will result in a valid file system.
#define BPB_TOTAL_SECTORS CFG_UF2_NUM_BLOCKS // Configuration ... up to 0x10209 / 0x101e9?
// #define BPB_TOTAL_SECTORS CFG_UF2_NUM_BLOCKS
#define BPB_TOTAL_SECTORS (0x101dd) // 0x101dd is absolute max at current code commit
#define BPB_MEDIA_DESCRIPTOR_BYTE (0xF8)
#define FAT_ENTRY_SIZE (2)
#define FAT_ENTRIES_PER_SECTOR (BPB_SECTOR_SIZE / FAT_ENTRY_SIZE)
@@ -125,6 +125,17 @@ STATIC_ASSERT(NUM_DIRENTRIES < (DIRENTRIES_PER_SECTOR * ROOT_DIR_SECTOR_COUNT));
STATIC_ASSERT(NUM_DIRENTRIES < BPB_ROOT_DIR_ENTRIES); // FAT requirement -- Ensures BPB reserves sufficient entries for all files
STATIC_ASSERT(NUM_DIRENTRIES < DIRENTRIES_PER_SECTOR); // GhostFAT bug workaround -- else, code overflows buffer
#define NUM_SECTORS_IN_DATA_REGION (BPB_TOTAL_SECTORS - BPB_RESERVED_SECTORS - (BPB_NUMBER_OF_FATS * BPB_SECTORS_PER_FAT) - ROOT_DIR_SECTOR_COUNT)
#define CLUSTER_COUNT (NUM_SECTORS_IN_DATA_REGION / BPB_SECTORS_PER_CLUSTER)
// Ensure cluster count results in a valid FAT16 volume!
STATIC_ASSERT( CLUSTER_COUNT >= 0x0FF5 && CLUSTER_COUNT < 0xFFF5 );
// Many existing FAT implementations have small (1-16) off-by-one style errors
// So, avoid being within 32 of those limits for even greater compatibility.
STATIC_ASSERT( CLUSTER_COUNT >= 0x1015 && CLUSTER_COUNT < 0xFFD5 );
#define UF2_FIRMWARE_BYTES_PER_SECTOR 256
#define TRUE_USER_FLASH_SIZE (USER_FLASH_END-USER_FLASH_START)
STATIC_ASSERT(TRUE_USER_FLASH_SIZE % UF2_FIRMWARE_BYTES_PER_SECTOR == 0); // UF2 requirement -- overall size must be integral multiple of per-sector payload?