SC115 CS I/O 2G Flash Memory Drive with USB Interface
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12.3 SC115 with Large Data Compliment
An SC115 with a large compliment of data (either a large number of files, or a
few very large files) may respond slower than an SC115 with less data.
Compiling data logger programs from a full SC115 may take longer than
normal.
Opening the SC115 directory in support software
File Control
also takes
longer if there are a large number of files within the SC115 directory.
File
Control
can access approximately twenty files per second when opening the
directory.
12.4 Data Collection Speed
Many factors affect collection speed in plug and pull data-collection mode. As
a rough estimate, collection speed is typically 3 to 4 kB of SC115 file size per
second (TFOption = 8, SDC7 set to –115200 [autobaud], no card storage
module present). Following are descriptions of two factors that contribute
significantly to the slowing of collection speed.
12.4.1 External Memory Card and Collection Speed
Following is a discussion of SC115 performance expectations when it is used
in tandem (plug and pull data-collection mode) with a resident external
memory card on a data logger.
Background – When an SC115 is configured for data-collection mode (plug
and pull), and it is plugged into a data logger with a resident external memory
card, and the running program is using the
CardOut()
instruction, all data
present since the last collection will be automatically transferred from the data
table to the SC115 file.
How it works – When
CardOut
is used in a
DataTable()
/
EndTable
declaration, the file created on the external memory card becomes an extension
of the table memory. The internal memory is used as a buffer to transfer data to
the external memory card. When there are enough data to warrant a write to the
external memory card, the data is flushed to the card. This results in duplicate
data, up to the internal table size, that will exist on the internal memory and the
external memory card files. Any time the table data is 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 is transferred first, then the external memory 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 external memory card adds some
overhead, but the vast majority of time is spent converting to ASCII and
transferring across a slow serial link.
Take home – external memory card to SC115 transfer of data is about 30 to
50% slower than data logger CPU to SC115 transfer of data. For example, in
testing with a CR1000 data logger with a 2 GB card attached, transfer of a
3.9 MB file (so no data were stored to the card) took aproximatel
y 1
6 minutes
(about 250 kB per minute). However, the rate of transfer slowed to about
