 File I/O Products
smxFile™
DOS-Compatible Reentrant File Manager
Product Description
smxFile™ is a robust, DOS-compatible file system for hard real-time embedded systems. It supports all device types commonly used in embedded systems. smxFile features high-performance file i/o and also provides disk directory management.
smxFile is written in ANSI C. Source code is provided. The API is similar to POSIX and DOS. The device driver interface is similar to UNIX, but simpler. smxFile operates in x86 real mode and in x86 16-bit and 32-bit protected modes. It also operates with PowerPC, ColdFire, ARM, and other processors.
This package is the latest in a series of DOS file system software packages that have been marketed since 1987. It and its predecessors have been included in hundreds of commercial embedded applications.
smxFile is integrated with smx. As many tasks, as desired, may perform simultaneous file i/o. Low-level i/o calls to the same disk are serialized via semaphores (since actual disk operations are inherently non-reentrant).
File Allocation Table (FAT)
The FAT is a structure on a disk that maps the blocks of disk space occupied by individual files on that disk. These blocks are called clusters. A cluster is a group of sectors, which is the smallest addressable units of a disk. Sectors are 512 bytes in size. The number of sectors per cluster is constant for the entire disk or partition[1]. Files typically contain many clusters.
FAT entries are in the same order as physical clusters on the disk and correspond one for one with them. Each FAT entry points to the next FAT entry for the same file or directory (Note: Directories are treated as files). A special value indicates the end of the file. The size of FAT entry dictates the size of the FAT and the maximum size of the disk. There are 3 common FAT entry sizes in use: FAT12, FAT16, and FAT32. On a FAT12 disk, for example, each FAT entry is a 12-bit number. All FAT’s have 18 reserved values (end of file, bad cluster, etc), so the number of FAT entries is given by 2n – 18 (where n = 12, 16, or 32).
FAT12 is used for small media such as floppy disks. FAT12 has up to 212 -18 = 4078 entries. Floppies are formatted for 1 sector per cluster which means the largest disk supported is almost 2 megabytes (512 * 4078).
As the number of sectors per cluster is increased, so is the maximum size of the disk which can be supported.
FAT16 is used for larger media such as hard disks. FAT16 has up to 64K-18 entries. Cluster size varies from 4 to 64 sectors (2KB to 32KB), allowing a maximum disk size of almost 2 gigabytes. smxFile allows caching (i.e. storing in memory) of any number of FAT sectors of 256 entries, each. To cache the entire FAT requires 128KB of RAM. Caching more sectors of the FAT improves performance by reducing the disk accesses for the FAT, itself. (Since the FAT is stored at the beginning of the disk, the drive head must frequently sweep back and forth from the data area to the FAT area. This may cause unacceptable perfoemance if there is insufficient FAT caching.)
FAT32 is used for very large media, such as multi-gigabyte hard disks. FAT32 cluster size varies from 8 to 64 sectors each (4KB to 32KB), and allows a maximum disk size of 2 terabytes. smxFile allows caching any number of FAT blocks for 32-bit memory models[2] (16-bit memory models, such as real mode, are limited to a 128KB cache). Since each entry is 32 bits, each sector of the FAT stores only half as many entries as FAT16. For hard drives, commonly in use today, the FAT occupies thousands of sectors, so it is often impractical to cache the entire FAT. A high performance, streaming application might cache as many as 500 sectors of the FAT. The best cache size for an application is determined by experimentation.
Contiguous Files
smxFile permits preassigning contiguous clusters to a file, if available. This permits high transfer rates because track motion is reduced for FAT accessing successive file clusters. Since FAT entries for successive file clusters are adjacent, less FAT acesses are also required.
Long File Names
smxFile has long file name (VFAT) support. It will read and write Microsoft Windows 9x-compatible, long file names. Unfortunately, Microsoft has a patent on this technology so we ship with this feature disabled. It can be enabled by a single setting.
smxFile Drivers
smxFile supports most storage devices commonly used in embedded systems. Devices are supported are as follows:
Floppy driver: Supports 3.5" and 5.25" floppy disks of all capacities (360K, 1.2MB, 720K, and 1.44MB). It supports NEC 765 compatible controllers. Dual drives are supported.
IDE/ATA driver: Supports all IDE hard disks and Compact Flash. Interrupt or polled mode. Has timeout protection.
IDE Ultra DMA driver: Supports all IDE hard disks and offers Ultra DMA/33 support for drives and controllers with this feature. DMA/44 and DMA/66 are also supported. Code is included to probe the PCI BIOS for the configuration of the bus-mastering DMA controller.
USB Mass Storage driver: Supports USB disks. Tested on many USB flash drives (v1.1 and v2.0).
PCMCIA ATA driver: Supports PCMCIA ATA disks and PD67xx- compatible PCMCIA controllers. Also permits hot swapping and supports Compact Flash.
DiskOnChip® driver: Supports the M-Systems DiskOnChip 2000 and Millenium. Based upon M-Systems proprietary TrueFFS® technology. Co-developed by M-Systems and Micro Digital. Source code not included but may be available by special arrangement with M-Systems.
ATAPI driver includes:
- LS-120 driver: Supports all LS-120 drives. Also known as SuperDisk®.
- Zip® driver: Supports 100MB and 250MB Iomega Zip disks.
SCSI driver: Supports SYMBIOS 53C8xx SCSI controllers for SCSI hard disks.
RAMdisk and ROMdisk drivers: Included with smxFile. A ROMdisk builder utility is also included.
BIOS driver: Available in x86 real-mode, only. Allows using any BIOS (int 13H) disk driver such as a resident flash disk driver.
CD-ROM
CD-ROM actually requires a separate file system. Ask about our smxCD. smxFile and smxCD can run simultaneously in the same system.
If the storage device you require is not in the above list, contact us — it may be under development.
API Functions
The following functions constitute the smxFileAPI. These functions have been categorized for convenience. All functions are "task-safe" — i.e. can be accessed simultaneously from different tasks. As is apparent from the following list, the smxFileAPI is quite powerful and complete. However, for those preferring the DOS or Win32 API's, unDOS or unWin can be used in combination with smxFile.
| File I/O Functions |
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| po_chsize |
Extend or truncate a file |
| po_close |
Close a file |
| po_flush |
Flush a file to disk |
| po_lseek |
Move file pointer |
| po_open |
Open a file |
| po_read |
Read from a file |
| po_truncate |
Truncate a file |
| po_write |
Write to a file |
| |
|
| File Management |
| |
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| pc_fstat |
Obtain statistics on an open file |
| pc_get_attributes |
Get file attributes |
| pc_mv |
Rename a file or directory |
| pc_set_attributes |
Set file attributes |
| pc_unlink |
Delete a file |
| |
|
| Directory Management |
| |
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| pc_deltree |
Delete a directory tree |
| pc_gdone |
Free pc_gnext and pc_gfirst resources |
| pc_get_cwd |
Get current working directory |
| pc_gfirst |
Return the first entry in a directory matching specified pattern |
| pc_gnext |
Return next entry in a directory matching specified pattern |
| pc_isdir |
Test if a path is a directory |
| pc_mkdir |
Create a subdirectory |
| pc_pwd |
Return the current working directory |
| pc_rmdir |
Delete a directory |
| pc_set_cwd |
Set current working directory |
| |
|
| Disk Management |
| |
|
| pc_cluster_size |
Return a disk's cluster size |
| pc_diskabort |
Abort operations on a disk without modifying disk. |
| pc_diskflush |
Flush the FAT and all files to a disk |
| pc_format |
Format a disk |
| pc_free |
Return count of free bytes on disk |
| pc_getdfltdrvno |
Return the current default drive number |
| pc_isvol |
Test if a path is a volume name |
| pc_set_default_drive |
Set the default drive |
| pc_stat |
Obtain statistics on a path |
| pc_write_protect |
Indicates whether media is write protected (floppy only, currently) |
| |
|
| Contiguous I/O Functions |
| |
|
| pc_get_file_extents |
Get the list of clusters that make up a file |
| pc_get_free_list |
Get a list of free clusters on the drive |
| pc_raw_read |
Read blocks directly from a disk |
| pc_raw_write |
Write blocks directly to a disk |
| po_extend_file |
Extend a file with contiguous clusters |
Additional Support
In addition to the preceding API functions, numerous low-level functions are provided for:
(1) initialization
(2) directory management
(3) helper functions
(4) block buffering
(5) string processing
These are normally not needed at the application level, but are available, if needed. The string functions may be useful for other purposes. The package also includes a simplified sprintf().
Drives
The number of drives of each type is specified in pcconf.h. The order of definition and the number of each type determine drive lettering.
Code Sizes
smxFile, with IDE and floppy drivers is approximately 55 KB for a 32-bit x86 processor.
Performance
smxFile, with the Ultra-DMA driver, will support sustained data transfer rates of 20 MByte/sec (measured on a 20GB 7200 rpm drive). Performance depends on the density and rotational speed of the drive.
RAM Usage
RAM usage is tunable. It is determined by configuration parameters in pcconf.h. Memory is allocated statically from the BSS segment/section. The configuration parameters are:
| FAT_CACHE_SIZE |
of sectors of FAT that are cached in memory |
| NBLKBUFFS |
Number of blocks in the buffer pool. (Which stores disk sectors during directory traversals.) |
| NUM_USERS |
number of tasks that may access the file system |
| NUSERFILES |
Maximum number of open files |
In addition, tasks using smxFile require stacks of about 1500 bytes for 16-bit memory models or 2500 for 32-bit memory models.
What is Delivered
- Full source code, including purchased drivers
- Manual
- Make file to build the smxFileand driver library
- Demo
Notes
- A disk can be divided into separate partitions, each with its own cluster size.
- 16-bit memory models, such as real mode, are limited to a 128KB cache.
For More Information
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