Clean up the VirtualFAT implementation.

[pub/USBasp.git] / Bootloaders / MassStorage / Lib / VirtualFAT.c

diff --git a/Bootloaders/MassStorage/Lib/VirtualFAT.c b/Bootloaders/MassStorage/Lib/VirtualFAT.c
index 569b754..2772c17 100644 (file)
--- a/Bootloaders/MassStorage/Lib/VirtualFAT.c
+++ b/Bootloaders/MassStorage/Lib/VirtualFAT.c
@@ -139,11 +139,12 @@ static FATDirectoryEntry_t FirmwareFileEntries[] =
                },
        };
 
-/** Starting block of the virtual firmware file image on disk. On Windows, files
- *  are (usually?) replaced using the original file's physical sectors. On Linux
- *  file replacements are performed with an offset.
+/** Starting cluster of the virtual firmware file on disk, tracked so that the
+ *  offset from the start of the data sector can be determined. On Windows
+ *  systems files are usually replaced using the original file's disk clusters,
+ *  while Linux appears to overwrite with an offset which must be compensated for.
  */
-static uint16_t FileStartBlock = DISK_BLOCK_DataStartBlock;
+static uint16_t* FileStartCluster = &FirmwareFileEntries[DISK_FILE_ENTRY_FirmwareMSDOS].MSDOS_File.StartingCluster;
 
 
 /** Updates a FAT12 cluster entry in the FAT file table with the specified next
@@ -192,9 +193,12 @@ static void ReadWriteFirmwareFileBlock(const uint16_t BlockNumber,
                                        uint8_t* BlockBuffer,
                                        const bool Read)
 {
+       uint16_t FileStartBlock = DISK_BLOCK_DataStartBlock + (*FileStartCluster - 2) * SECTOR_PER_CLUSTER;
+       uint16_t FileEndBlock   = FileStartBlock + (FILE_SECTORS(FIRMWARE_FILE_SIZE_BYTES) - 1);
+
        /* Range check the write request - abort if requested block is not within the
         * virtual firmware file sector range */
-       if (!((BlockNumber >= FileStartBlock) && (BlockNumber < (FileStartBlock + FILE_SECTORS(FIRMWARE_FILE_SIZE_BYTES)))))
+       if (!((BlockNumber >= FileStartBlock) && (BlockNumber <= FileEndBlock)))
          return;
 
        #if (FLASHEND > 0xFFFF)
@@ -265,11 +269,6 @@ void VirtualFAT_WriteBlock(const uint16_t BlockNumber)
                        /* Copy over the updated directory entries */
                        memcpy(FirmwareFileEntries, BlockBuffer, sizeof(FirmwareFileEntries));
 
-                       /* Save the new firmware file block offset so the written and read file
-                        * contents can be correctly mapped to the device's FLASH pages */
-                       FileStartBlock = DISK_BLOCK_DataStartBlock +
-                                        (FirmwareFileEntries[DISK_FILE_ENTRY_FirmwareMSDOS].MSDOS_File.StartingCluster - 2) * SECTOR_PER_CLUSTER;
-
                        break;
 
                default:
@@ -311,7 +310,7 @@ void VirtualFAT_ReadBlock(const uint16_t BlockNumber)
                        /* Cluster 2 onwards: Cluster chain of FIRMWARE.BIN */
                        for (uint16_t i = 0; i <= FILE_CLUSTERS(FIRMWARE_FILE_SIZE_BYTES); i++)
                        {
-                               uint16_t CurrentCluster = FirmwareFileEntries[DISK_FILE_ENTRY_FirmwareMSDOS].MSDOS_File.StartingCluster + i;
+                               uint16_t CurrentCluster = *FileStartCluster + i;
                                uint16_t NextCluster    = CurrentCluster + 1;
 
                                /* Mark last cluster as end of file */