Campbell Scientific CR3000 CR3000 Micrologger - Page 276
TableFile, Status
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Section 7. Installation 276 data to be continuously and more quickly written to the card in ≈1 KB blocks. TOB3 binary format copies data directly from CPU memory to the CF card without format conversion, lending additional speed and efficiency to the data storage process. Note Pre-allocation of CF card files significantly increases run time write performance. It also reduces the risk of file corruption that can occur as a result of power loss or incorrect card removal. Note To avoid data corruption and loss, CF card removal must always be initiated by pressing the initiate card removal button on the face of the NL115 or CFM100 modules. The card must only be ejected after the status light shows a solid green. Q: Why are individual files limited to 2 GB? A: In common with many other systems, the datalogger natively supports signed4-byte integers. This data type can represent a number as large as 231, or in terms of bytes, roughly 2 GB. This is the maximum file length that can be represented in the datalogger directory table. Q: Why does a large card cause long program compile times? A: Program compile times increase with card and file sizes. As the datalogger boots up, the card must be searched to determine space available for data storage. In addition, for tables that are created by TableFile() with Option 64, an empty file that is large enough to hold all of the specified records must be created (i.e., memory is pre-allocated). When using TableFile() with Option 64, program compile times can be lessened by reducing the number of records or data interval that will be included in each file. For example, if the maximum file size specified is 2 GB, the datalogger must scan through and pre-allocate 2 GB of CF card memory. However, if smaller files are specified, then compile times are reduced because the datalogger is only required to scan through enough memory to preallocate memory for the smaller file. Q: Why does a freshly formatted card cause long compile times? A: Program compile times take longer with freshly formatted cards because the cards use a FAT32 system (File Allocation Table with 32 table element bits) to be compatible with PCs. To save time, use a PC to format CF cards. After formatting the card, write any file to the card, then delete the file. This action sets up the card for faster initial use. FAT32 uses an "info sector" to store the free cluster information. This info sector prevents the need to repeatedly traverse the FAT for the bytes free information. After a card is formatted by a PC, the info sector is not automatically updated. Therefore, when the datalogger boots up, it must determine the bytes available on the card prior to loading the Status table. Traversing the entire FAT of a 16 GB card can take up to 30 minutes or more. However, subsequent compile times are much shorter because the info sector is used to update the bytes free information. To avoid long compile times on a freshly formatted card, format the card on a PC, then copy a small file to the card, and then delete the file (while still in the PC). Copying the file to the freshly formatted card forces the PC to update the info sector. The PC is much faster than the datalogger at updating the info sector.