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Fix dynamic FAT variant detection #55 (#56)
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* Fix FAT32 format check #55
Only the first two bytes were considered when reading the end-of-chain value from the FAT table. Extend to 4 bytes and relax requirement for first 3 bits.
Make requirement for FAT12 more strict because all valid, non-reserved cluster bits must be set.
* Fix inverted FAT12 logic
* Add default heap selection to CMakeListst.txt
---------
Co-authored-by: Hein Tibosch <hein_tibosch@yahoo.es>
Co-authored-by: Soren Ptak <ptaksoren@gmail.com>
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@cookpate
cookpate authored Nov 30, 2023
1 parent 25129e5 commit 086960f
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Showing 2 changed files with 47 additions and 21 deletions.
6 changes: 6 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,12 @@ elseif((FREERTOS_PLUS_FAT_PORT STREQUAL "A_CUSTOM_PORT") AND (NOT TARGET freerto
" freertos_plus_fat)")
endif()

# This library requires access to a heap
# FreeRTOS/FreeRTOS-Kernel previously defaulted to heap4.c
if(NOT DEFINED FREERTOS_HEAP)
message(STATUS "FREERTOS_HEAP not set, setting FREERTOS_HEAP=4")
set(FREERTOS_HEAP 4)
endif()

# Select the appropriate Build Test configuration
# This is only used when freertos_config is not defined, otherwise the build test will be performed
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62 changes: 41 additions & 21 deletions ff_ioman.c
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Original file line number Diff line number Diff line change
Expand Up @@ -705,18 +705,21 @@ static uint8_t ucAssumeFATType = 0;
*
* In practice however, this does not always seem to be a correct assumption.
*
* The first 12 or 16 bits in the FAT table may also help to determine the
* The end-of-chain value in the FAT table may also help to determine the
* correct FAT-type:
*
* FAT-12: ( firstWord & 0x3FF ) == 0x3F8 )
* FAT-16: ( firstWord == 0xFFF8 )
* ulFirstCluster = the first 32-bit of the FAT.
* FAT-12: endOfChain == 0x00000FF8 - 12 bits
* FAT-16: endOfChain == 0x0000FFF8 - 16 bits
* FAT-32: endOfChain == 0x0FFFFFF8 - 32 bits
*/

static FF_Error_t prvDetermineFatType( FF_IOManager_t * pxIOManager )
{
FF_Partition_t * pxPartition;
FF_Buffer_t * pxBuffer;
uint32_t ulFirstWord = 0ul;
/* The first 32-bits of the FAT. */
uint32_t ulFirstCluster = 0U;
FF_Error_t xError = FF_ERR_NONE;

pxPartition = &( pxIOManager->xPartition );
Expand Down Expand Up @@ -751,7 +754,8 @@ static FF_Error_t prvDetermineFatType( FF_IOManager_t * pxIOManager )
}
else
{
ulFirstWord = ( uint32_t ) FF_getShort( pxBuffer->pucBuffer, 0x0000 );
/* Read the first 4 bytes at offset 0. */
ulFirstCluster = FF_getLong( pxBuffer->pucBuffer, 0U );
xError = FF_ReleaseBuffer( pxIOManager, pxBuffer );
}
}
Expand All @@ -764,13 +768,23 @@ static FF_Error_t prvDetermineFatType( FF_IOManager_t * pxIOManager )
/* FAT12 */
pxPartition->ucType = FF_T_FAT12;
#if ( ffconfigFAT_CHECK != 0 )
if( ( ulFirstWord & 0x3FF ) != 0x3F8 )
/* Keep bits 4..11 */

/* MS-DOS/PC DOS 3.3 and higher treats a value of 0xFF0 on FAT12.
* See https://en.wikipedia.org/wiki/Design_of_the_FAT_file_system
*/
ulFirstCluster &= 0xFF0U;

if( ulFirstCluster != 0xFF0U )
{
xError = FF_createERR( FF_ERR_IOMAN_NOT_FAT_FORMATTED, FF_DETERMINEFATTYPE );
FF_PRINTF( "FAT_CHECK: FAT12 Partition has unexpected FAT data %04lX\n",
ulFirstCluster );
}
else
#endif /* ffconfigFAT_CHECK */
{
/* FAT12 entry OK. */
xError = FF_ERR_NONE;
}
}
Expand All @@ -783,20 +797,24 @@ static FF_Error_t prvDetermineFatType( FF_IOManager_t * pxIOManager )
pxPartition->ucType = FF_T_FAT16;
#if ( ffconfigFAT_CHECK != 0 )
{
if( ulFirstWord == 0xFFF8 )
/* Keep bits 4..15 */
ulFirstCluster &= 0xFFF8U;

if( ulFirstCluster == 0xFFF8U )
{
/* FAT16 entry OK. */
xError = FF_ERR_NONE;
}
else
{
if( ( ulFirstWord & 0x3FF ) != 0x3F8 )
if( ( ulFirstCluster & 0xFF8U ) == 0xFF8U )
{
FF_PRINTF( "Part at %lu is probably a FAT12\n", pxIOManager->xPartition.ulFATBeginLBA );
FF_PRINTF( "FAT_CHECK: FAT16 Part at %lu is probably a FAT12\n", pxIOManager->xPartition.ulFATBeginLBA );
}
else
{
FF_PRINTF( "Partition at %lu has strange FAT data %08lX\n",
pxIOManager->xPartition.ulFATBeginLBA, ulFirstWord );
FF_PRINTF( "FAT_CHECK: FAT16 Partition has unexpected FAT data %08lX\n",
ulFirstCluster );
}

xError = FF_createERR( FF_ERR_IOMAN_INVALID_FORMAT, FF_DETERMINEFATTYPE );
Expand All @@ -809,19 +827,21 @@ static FF_Error_t prvDetermineFatType( FF_IOManager_t * pxIOManager )
/* FAT 32! */
pxPartition->ucType = FF_T_FAT32;
#if ( ffconfigFAT_CHECK != 0 )
if( ( ( ulFirstWord & 0x0FFFFFF8 ) != 0x0FFFFFF8 ) &&
( ( ulFirstWord & 0x0FFFFFF8 ) != 0x0FFFFFF0 ) )
/* Keep bits 4..27 */
ulFirstCluster &= 0x0FFFFFF8UL;

if( ulFirstCluster != 0x0FFFFFF8UL )
{
/* _HT_
* I had an SD-card which worked well in Linux/W32
* but FreeRTOS+FAT returned me this error
* So for me I left out this check (just issue a warning for now)
*/
FF_PRINTF( "prvDetermineFatType: firstWord %08lX\n", ulFirstWord );
xError = FF_ERR_NONE; /* FF_ERR_IOMAN_NOT_FAT_FORMATTED; */
FF_PRINTF( "FAT_CHECK: FAT32 Partition at %lu has unexpected FAT data %08lX\n",
pxIOManager->xPartition.ulFATBeginLBA, ulFirstCluster );
xError = FF_ERR_IOMAN_NOT_FAT_FORMATTED;
}
else
#endif /* ffconfigFAT_CHECK */
xError = FF_ERR_NONE;
{
/* FAT32 entry OK. */
xError = FF_ERR_NONE;
}
}
}

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