Guralp Systems CMG-DCM build <10,000 - Manual (Page 256)

Acquisition Modules and Platinum Firmware Technical operation
15.1.3.1 USB device mode
The Cylindrical Digitiser is fitted with an internal Flash memory device
which is accessible via USB. It can be written to by selecting “Internal USB
storage” from the “Recording destination” drop-down menu on the “Disk
recording” page (see section 11.2 on page 138).
When a USB host, such as a laptop or PC, is connected to the GPIO port
(who's pin-out is given in section 16.5.6 on page 278) internal circuitry detects
the USB power and automatically connects the Flash memory to the GPIO
socket, causing it to behave identically to a standard USB memory stick.
When no power is detected at the GPIO port, the Flash memory is available to
the system as if it were a standard removable mass storage device. All of the
mass storage device recording options described in section 11.2 (on page 138)
will apply to this device.
15.1.3.2 USB host mode
If a USB storage device is connected to the USB port (see section 16.5.8 on
page 280 for the pin-out), it will be mounted under /media. It can be used to
store seismic data by selecting “External USB drive on mil-spec connector”
from the “Recording destination” drop-down menu on the “Disk recording”
menu (see section 11.2 on page 138).
15.2 DCM
The DCM is a fully-functional, Linux-based computer system especially
designed for handling seismic data. It can collect and store data from several
sources and, if required, output it in your preferred format to other locations
on your network or on the Internet. The CMG-DCM receives data from one or
more of the following sources:
• Digitizer connected through a serial link
• Computer running a Scream server
• CD1.0 or CD1.1 transmitter (optionally)
• Another DCM or AM
All the received data are stored in files in the on-board Flash memory. There
are two banks of Flash memory available, which are accessible as /nand0 and
/nand1 in the Linux file tree. Data are normally stored as GCF (Güralp
Compressed Format) files.
As an option, you may be able to configure the DCM to use the miniSEED or
sac formats instead.
In automatic mode, when the Flash memory becomes more than 75% full, the
oldest data files are moved to the DCM's primary hard disk until it is less than
MAN-EAM-0003 256 Issue E - February 2014