Globalstar Product Management – Technical Support

Avoiding Erratic GSP-1620 Behavior

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The GSP-1620 is an exceptionally stable satellite modem as long as simple guidelines are followed when powering the modem on and off.

Background:
The GSP-1620 Integrator’s Reference Manual (page 7-18) provides clear instructions for powering down the GSP-1620.  If this procedure is NOT followed, and power to the GSP-1620 is abruptly terminated, the modem’s NVRAM can become corrupted, which leads to unexpected problems with seemingly inexplicable symptoms.  For example,

  1. The modem can remain locked onto the frequency of an incorrect gateway, and never initiate a search for a gateway that could provide service.
  2. The modem can become unable to interpret some AT commands, while properly processing other commands.
  3. AT$QCSTATUS can yield responses such as “MODE: NO_MODE” and other oddities.

It is not productive to list all the possible perturbations of problems which can arise from corrupted NVRAM.  The common element to NVRAM corruption is that the modem is generally not able to establish satellite communications.  Another characteristic of NVRAM corruption is that the behavior can be erratic, sometimes leading to problems and other times not causing any problems.  A modem in this state will generally remain non-functional forever, until it is powered off properly, and then powered back on.  Overall, the behavior leads the user to believe that the Globalstar system is not operational when, in fact, if the modem had simply been power-cycled properly, service would have been obtained immediately.

Solution:
We recommend either of the following two methods to restore the NVRAM of a GSP-1620:

  1. Power up the GSP-1620, wait for it to fully boot, and then power down the GSP-1620 following the procedure specified in the Integrator’s Reference Manual.
  2. Hold pin 25 of the GSP-1620 DB25 to ground for five seconds when you first apply power to the modem.  Then, after five seconds has elapsed, release pin 25 and allow its voltage to float.

Using either of these methods will ensure that the modem will automatically reboot with a fully reset NVRAM, regardless of how it had been shut down previously.  There is no need to use both methods; one method is sufficient.

Recommendation:
We strongly recommend that GSP-1620 integrators use one of the above-mentioned methods to ensure that the modem is fully ready for communications every time it is powered on.  Although it is fairly simple to power a modem off gracefully in a lab situation, it is basically impossible to force this regimen on a general user.  If the user abruptly de-powers the modem, the integrated product may well become inoperable unless the product has an onboard backup battery along with an onboard shutdown processor.  For various reasons – explosion concerns, cost, complexity, weight, etc. – this sort of design is not commonly used by modem integrators.  However it is quite reasonable for the modem integrator to incorporate a longer boot sequence into the modem device, using one of the methods described above, so that the user has no choice but to wait the extra five seconds it will take to boot up the modem.  Most users won’t even notice this extra boot time.

For situations where the extra five-second boot time is unacceptable, the integrator must ensure that the modem is shut down gracefully so that it is fully ready to communicate the next time it is powered on.

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Written by Joseph Crowley

August 21, 2008 at 8:59 pm

Posted in GSP-1620

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