APPNOTE: USB Memory Device operations in the PM7000

Article ID: 071005jdo
Last Reviewed: June 30, 2011

The information in the article applies to:

  • Ranger Power Master PM7000.

Target Audience.

This article is aimed at:

  • All users of the PM7000

Summary.

A USB Memory device (variously known as a USB Flash Drive, Jump Drive, Cruzer, USB Memory Stick etc) may be used to transfer data from the PM7000 to a computer instead of performing the download over the serial USB, Ethernet or Bluetooth links.

USB Memory Device limitations.

The drivers for USB memory devices used in the PM7000 have the following limitations:
Partition formats supported: FAT12, FAT16 and FAT32.
Partition Size Limit: untested but I suspect there is a limit at 128 GB.
Number of files in a directory: 1022 ( or 65534 ).
The Drivers in the PM7000 are unable to allocate additional clusters to a directory. As each file uses 32 bytes from the directory in which it resides, for a drive formatted with 32768 byte clusters this limit is reached when 1022 files are present. For a drive formatted with smaller clusters the limit is corresponding smaller, for example, 4096 byte clusters would hit this limit at 126 files.

Limitations in Windows 2000 / XP / Vista / 7.
There is a FAT32 Partition creation size limit of 32 GB when using the disk management tool. This limitation can be worked round by using the command line and typing the command
> format x: /fs:FAT32 /a:32k
Where x is the letter of the drive you wish to format.

Choice and formatting of Memory Devices

Clearly large devices are more useful than small ones. However some large devices may be built using a multi-level cell technology (MLC) which may make them slower than other single level cell devices (SLC).

The device is divided into “sectors” and “clusters”. The number of clusters and the size of each one (from 512 bytes up to 32768 bytes) are set in the device formatting process. Each cluster is used to hold one file or part of a file. Large files are held in multiple clusters, and the sequence of clusters as well as other file details are held in the “File Allocation Table” (FAT).  Because an entire cluster is the minimum space allocated to a single file, small memory devices tend to come formatted with relatively small clusters. This enables a large number of small files to be stored efficiently, whereas larger clusters are inefficient and wasteful if typical files are small.  However there is a speed overhead associated with the housekeeping of small clusters which is reduced when cluster size is increased. Consequently larger devices tend to be formatted with larger clusters, since speed is likely to be more significant than the waste associated with small files.

PM7000 files come into the large category, therefore whatever size of device is chosen, it should be formatted with the largest clusters possible, ideally 32kByte.

To format (or reformat) a device AND to specify the cluster size,

  1. Insert the USB device into a USB port on your PC, then under Windows “My Computer”, select “Control Panel/Administrative Tools/Computer Management/Disk Management”.
  2. Allow the PC to find the disk drives present, which should include the USB Memory Device. You may have to expand the size of the window pane offered.
  3. Identify the relevant drive and BE CERTAIN that it is not crucial to the computer’s operation.
    Beware the format function is very powerful and if you format the PC’s hard drive inadvertently you will lose all your data and your programs.
  4. Having identified the correct drive, right click on it, and select “Format”. You will be asked “are you sure you want to format this partition?” Click yes.
  5. The volume label may be left as it is. If the File system offers “FAT”, choose this rather than “FAT32”, as it is slightly faster in operation. Large devices are likely to be FAT32 and you won’t have any choice. For the Allocation Unit Size (Cluster size), choose 32k. Click OK.
  6. At the warning message, click OK.
  7. If the operating system is happy to format the drive with the cluster size selected, it will format the drive and return to the display of all the disk drives present. If you get the error message “The Cluster size is too big for the selected file system” , you should repeat the process from step (4) and select the next cluster size down. If that also produces the same “Cluster size too big” message, repeat the process from (4) again, selecting smaller and smaller cluster sizes until the operating system is happy.

Close down successive windows until you are back at the desktop again.

Note that a slow drive, formatted with small clusters, may be as much as 20 times slower than a large device optimally formatted.  

Manual Copy.

To copy recorded sessions from the PM7000 to the USB Memory Device, insert the memory device into the “host” slot in the PM7000 communications bulge towards the back of the unit.

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The Memory device will only slot in one way up. It is usually with the  USB symbol img2.gif  uppermost.

With PMScreen running either on a PC or a PDA,

Stop the recording (you may only copy completed recordings) and allow the copy of wave capture data from RAM to internal Flash memory to finish.

From the logger “Main Menu”, select “Explore” (a). This will display all the sessions held on the logger’s Flash Drive, and available for copy to the memory device (b).

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     (c)

To copy all of them, choose “Select All”. If you want to copy only one, select that session by pressing on it. If there are more sessions than fit on the screen, you may use the scroll buttons to bring the sessions of interest onto the screen, where you can select one by pressing on it.

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If the system has recognised the Memory Device, the LED on the PM7000 front panel will have gone green, and the Button “Copy to USB Device” will be active (c). Select this button to start the copy process. Note the front panel LED will go red during the copy process and the MEMORY DEVICE SHOULD NOT BE DISTURBED while copy or verify is in progress. When copy is complete and verified the LED will become green again, and the device may be removed.

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Note that the internal PM7000 USB interface circuit is energised only during the “Explore” mode, and all the time the LED is off or green, the Memory Device may be removed.

Automatic Copy at the end of a session

The USB Memory device may be inserted or withdrawn at any time provided the LED is not red.

An Automatic copy process occurs simply if a USB memory Device is detected when a recording ends automatically. Thus if a device is inserted during a recording, and is still in place at the end of a recording, any sessions in the PM7000 not already copied will be copied to the USB device. This does NOT apply if the recording is stopped by the user deliberately. It DOES apply if the recording shuts down for any other reason including time expiry, loss of power, or exhaustion of memory.

When a session has been copied to a USB device, an attribute is set against that session in the PM7000’s Flash Drive, and the session is shown with a red bar beside it in the PM7000’s explorer window (e.g. Session 2 has been copied, Session 3 has not).

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 The Auto-Copy process only copies sessions not previously copied, however the manual process can copy any session.

Note that the USB device is normally energised approximately 15 seconds before the end of a recording, so the green LED will typically come on at that point. It will go red during the copy process, go briefly green at the end and then turn off again.

File Structure on the USB device

The sessions are copied one at a time onto the USB device, together with the appropriate configuration, to create a single file for that session. The process is as follows:

The logger reads its own serial number, and creates (if it doesn’t already exist) a directory (folder) on the USB device with the name including the serial number.  E.g. for files from logger serial number ending 0114, it would be PM7S0114.

The session file is placed in this directory, and automatically given a name similar to that used by Pronto for the datafiles read over the serial USB link. It also has the same form and the same file extension (.MDM). This naming arrangement is intended to uniquely identify the source, date and type of each file and to minimise the likelihood of file name conflicts.

The PM7000 first checks for the existence of the appropriate directory on the USB drive (creates it if necessary), and looks for files already in it with the same date. The file naming convention is YYMMDDXX.mdm,  where YY is the year (e.g. 06 for 2006), MM is the month, and DD the day of the month. XX is a suffix which begins at 00 for the first file of the day, and counts upwards for successive files. Thus the first file to be copied on  2nd December 2006 is named    06120200.mdm, and the second 06120201.mdm.

If the logger finds files of the same date already present it uses the next available index.  In the event that there are more than 100 files copied from a single logger during a day, the index XX is extended to use the least significant of the DAY digits. Thus the number sequence always advances with later files saved.

Import into Pronto

The simplest way to import the .mdm files into Pronto is to have Pronto already open on your PC, then to select them (the .mdm files on the USB device) with Windows Explorer, and drag and drop them into Pronto. Pronto will automatically import them as though they were from the direct serial connection to a logger. You have the same opportunity to select suitable projects etc in which to place the data, and for multiple sessions from the same logger, you may use the AutoSave function to append new data to old.

Memory extension by Automatic Copying

By the simple expedient of selecting FIFO (recycling) mode, the PM7000 can effectively extend its memory up to the capacity of the memory device. FIFO is found under the Configure / Record Mode and Times menu.

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As discussed above a device present at the end of a recording causes a copy of any uncopied sessions into the device (provided it wasn’t user-terminated). If FIFO is in operation the PM7000 will re-start recording automatically when a previous one is complete, deleting space in its own memory if necessary, and all the time the system finds a memory device present at the end of each recording, that recording (initially “uncopied”) is copied to the device. This process can continue until the memory device is full.

The memory allocation in the PM7000 is suggested to be approximately 32 – 48 MB. This ensures that a recording just completed does not have to be deleted straight away (since there will be 80 – 96MB spare space – plenty of room for another file of 32 or 48MB), hence the new recording can start immediately the previous wave capture data has been saved, and does not have to wait while the file is copied. In this way the time lost between recordings is a few seconds maximum rather than the full file copy time.

Specifying Start and Stop times.

A tidy way to obtain recordings starting and stopping at convenient times is to use the Delayed Start facility. Choose e.g. 24 hours or 7 days for the recording time, and use “setup Delay” (a)  to set a delayed start to occur at a precise future time (b).

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Figures (a) and (b)

Arrange the start time to be the next convenient time IN THE FUTURE, e.g. the next midnight  (c). When you “Accept” that, the “Start” (recording) process becomes “Start Timer” (d).

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Figures (c) and (d)

 Then the first recording will run midnight to midnight, and the second recording, though starting a second or two after midnight, will nevertheless run to midnight again. (In FIFO mode a new recording Stop Time is set by consideration of the “desired” stop time based on the previous Stop Time plus the chosen “Record time”. Thus the short period between recordings does not cause a gradual drift in recording start and stop times.)

Temperature of Operation

Note that USB Memory Devices are not usually specified to work outside the normal PC operating temperature range (typically 0-40 deg C). We have had mixed fortune trying to operate devices during product temperature testing (-20 to 60 deg C). Some work and some don’t.