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Prometheus-LC CPU User Manual V1.0 Page 23
Known Limitations
• RFD (onboard flash drive) is not compatible with DOS expanded memory configuration in
EMM386.EXE. Use the NOEMS switch appended to the end of the EMM386 line in your
config.sys to bypass EMS. Example line in config.sys:
device=c:\DOS\EMM386.exe NOEMS
• The onboard flash chip has a limitation of 2,000,000 erase cycles, so swap drives or
virtual memory functions should not be used.
• Only 16-bit operating systems are supported with this Onboard Flash. MSDOS 6.22,
ROMDOS 6.22 and 7.0, and FreeDOS have been tested. Other operating systems may
work as long as they have a 16-bit compatibility mode.
Life Cycle Management and Calculations
The Disk-On-Board feature provides a simple form of wear leveling. Each time data is written, the
next consecutive available memory space is used, and the current location is marked as garbage
and made available for later use. This way the system walks through the entire available space
before rewriting the current file location. This technique helps to dramatically increase the chip’s
lifetime, because the entire chip is used to spread out the wear caused by the repeated erase
cycles.
A typical embedded application consists of reading a file, updating it, and repeating the process
over and over again. The formula for calculating the number of times this may be done before the
flash reaches its limit is as follows:
Number of file writes = (size of chip / size of file) * lifetime of chip
Where size of chip = 1.45MB and lifetime of chip = 2,000,000. This formula reveals the increase
in lifetime provided by the wear leveling. The lifetime is increased by the ratio of the chip’s total
capacity to the file size.
To calculate the number of days the chip will last, simply factor in the number of updates per day:
Lifetime in days = number of file writes / file writes per day