83Plus:Software:usb8x/Asm Interface/MSD

The mass storage driver works through a series of U_CALL entry points, much like the HID driver.

It requires two RAM buffers, one for internal use and one for a sector buffer. File handles used for opened files (explained later) also require around 27 bytes. The size of all three of these buffers can be obtained through the MSDVersion U_CALL. The size of the internal buffer is typically 254 bytes and the sector buffer is 512 bytes.

The entry point which requires these buffers is the MSD_Initialize U_CALL. Its memory can be dynamically allocated to appBackUpScreen (taking up practically all of it) with the code below:

U_CALL MSDVersion
ld de,appBackUpScreen
push de
add hl,de
ex de,hl
pop hl
U_CALL MSD_Initialize

For file system operations, you will then make calls to UFI_Initialize and FAT_Initialize. All three of these will return with the carry flag set if there are problems, with more detailed information in offErrorCode.

If all three functions succeed, the following entry points can be called.

Entry Points

MSDVersion	Gets mass storage driver version and memory requirements
MSD_Initialize	Initializes mass storage driver
UFI_Initialize	Initializes connected mass storage device for sector read/write operations
UFI_Read	Reads sector at (MSDLBA) address into sector buffer
UFI_Write	Writes memory in sector buffer to (MSDLBA) address
FAT_Initialize	Initializes connected mass storage device for FAT16 file system operations
DOS_openFile	Opens a file and populates file handle with important information
DOS_fileSeek	Sets seek pointer for file handle to specified offset
DOS_fileRead	Read bytes from a file
DOS_fileWrite	Write bytes to a file and grow if necessary
DOS_createFile	Create new file in specified directory with size 0
DOS_createDirectory	Create new subdirectory in specified directory
DOS_deleteFileEntry	Delete file or folder (including contents)
DOS_countFilesInDir	Get number of files/folders in specified directory
DOS_getNextFile	Get first/next file in specified directory
DOS_getFileSize	Get size of file
DOS_getDirEntry	Get directory entry for specified file/folder
FAT_nameConvertTo11	Convert name to 11-character format (ex. "README TXT")
FAT_nameConvertFrom11	Convert name to ASCIIZ format (ex. "readme.txt")
FAT_lookupPath	Find whether specified file/directory exists
FAT_findFileInCluster	Get directory entry for a file in specified folder
FAT_getStartingCluster	Get starting cluster of specified directory