Campbell Scientific SC115 CS I/O 2G Flash Memory Drive with USB Interface - Manual (Page 25)

SC115 CS I/O 2G Flash Memory Drive with USB Interface
data are retrieved via LoggerNet data collection, or by using the TableFile()
instruction, the internal SRAM is searched first, then the card. So, when
operating the SC115 in plug and pull mode, SRAM data are transferred first,
then the CF card is searched.
Effect —The rate of transfer is slowed, not because of the search of the card,
but because of the serial communications and (even slower) if an ASCII
output file is selected. This is compounded by large data files that can occur
when the CardOut instruction is used. Searching the CF card adds some
overhead, but the vast majority of time is spent converting to ASCII and
transferring across a slow serial link.
Take home — CF card to SC115 transfer of data is about 30 to 50% slower
than datalogger CPU to SC115 transfer of data. For example, in testing with a
CR1000 datalogger with a 2 GB card attached, transfer of a 3.9 MB file (so no
data were stored to the card) took aproximately16 minutes (about 250 kB per
minute). However, the rate of transfer slowed to about 190 kB per minute
when datalogger CPU memory was allowed to ring (fill and overwrite oldest
data) many times, resulting in a large amount of data on the card that was no
longer present on the CPU. In this example, it took 116 minutes to transfer a
22 MB data file from the CF card to the SC115. In the case of very large data
files stored to the CF card, it makes more sense to swap CF cards (see the
CFM100 CompactFlash Module user manual, available at
www.campbellsci.com , for details), or use a resident SC115, rather than
milking the data with the SC115 in plug and pull mode.
12.4.2 Data Type Collection Speed
Data type declared in the TableFile() TFOption parameter can affect SC115
collection speed. Data are buffered in the datalogger as binary. While data are
collected, the datalogger converts the binary to the declared data type. TOB1
options are binary and require very little processor overhead to convert from
the binary buffer. TOA5, CSIXML, and JSON are ASCII options and are far
slower since they consume significant processor overhead to convert to ASCII
from the binary buffer. CSIXML is especially slow. The effects on collection
time will be particularly noticeable if the datalogger is running a long or
complex program. In short, if large files from numerous dataloggers need
collection, using the TOB1 format may save considerable time. Consult the
LoggerNet Instruction Manual for options available to convert TOB1 data files
on the PC to easier-to-read formats.
12.5 Slow PC Boot-up
Leaving an SC115 attached to a PC while it is booting up may cause a delay of
several minutes to the boot-up process on some computers. The PC will
continue to boot normally if the SC115 is removed. The SC115 can then be
inserted and used as normal.
12.6 Write Failure
A write failure (after retries) is interpreted to mean the memory is full. When a
write failure occurs, MaxFiles parameter in the TableFile() instruction is
adjusted to its current number. In addition, the datalogger enters ring mode,
overwriting the oldest file on the SC115 with the new data (as if the MaxFile
parameter was set to -1).
The timeout period between a failed write command and a retry is 8 seconds.
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