Globalstar Product Management – Technical Support

GSP-1620 Power Management

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It is very important to follow the proper procedure for powering the GSP-1620 OFF and powering the GSP-1620 modem ON.These include the instructions provided on page 7-18 of the GSP-1620 Integrator’s Reference Manual (IRM)   in conjunction with some additional criteria that must be satisfied.

Proper Power-OFF of the GSP-1620 involves:

  1. Deassert all DTRs on the board
  2. Ensure that the DSRs are deasserted
  3. Wait a full 25 seconds to allow dynamic parameters from the modem’s memory to be written to NVRAM
  4. Then and only then, remove power.

Proper Power-ON of the GSP-1620 involves:

  1. Assert either the Data_Port DTR or the Control_Port DTR on the GSP-1620
  2. Wait for the Power_On_Self_Test (POST) message to appear on the AT Command Port, i.e. SELF TEST RESULT: OK
    1. Wait a full 5 seconds AFTER the POST message is displayed before sending ANY characters, bytes or bits to the AT Command Port.
    2. If the POST message is not displayed, wait a full 20 seconds after assertion of DTR before sending any characters, bits or bytes to the AT command port
  3. The above_mentioned Power_ON wait times are critically important to the successful booting of the GSP-1620 modem.
    1. IMPORTANT: If the above Power_ON wait periods are not respected, the modem may boot into a non-standard state
    2. Do not send any characters or commands to the AT command port based simply on the fact that the modem may have asserted DSR.  DSR is not a sufficient indicator that the modem is completely booted up, and is ready to receive and perform AT commands
    3. If AT commands are sent to the modem before the above wait times have expired, the modem may react properly to some AT commands and not to others.  The behavior can be different with every user-caused bootup failure.


Power_OFF Symptoms

We have determined that the IRM is correct when it states that NVRAM of the board will be corrupted if the Power_OFF procedure is not followed.  When the NVRAM is corrupted, the modem may behave in unexpected ways when it powers up.  For example, the AT$QCSTATUS command issued from a modem in New England might display:

System Availability YES
Registration: No
Gateway: 1

Since the modem is in New England, it needs to be on Gateway 4, so that is why Gateway 1 rejected its registration.  Subsequent AT$QCSTATUS commands would normally be expected to display different gateway ID numbers, indicating that the modem is searching for a gateway where it can get Registration: YES.  However, we have seen instances where this does not happen after an improper Power_OFF sequence, and the modem stays in this “limbo” mode forever, until the modem is powered on/off properly.  The customer in this situation would report that he had no signal and no communication when, in fact, if he had simply power-cycled the modem properly, he would have obtained service immediately.

There are other examples of NVRAM problems, where AT$QCSTATUS yields responses like MODE: NO_MODE and also other oddities.  It is not productive to list all the possible perturbations of problems which can arise from corrupted NVRAM.  It is productive to ensure that your application is controlling the GSP-1620 Power_OFF sequence in the proper way because this will ensure that your data modem will have the highest reliability and the highest performance.

A common problem which integrators face is that their end-users simply want to yank the plug on the device when they are done with their job, and do not understand the importance of going through a graceful shutdown of the modem.  Or, it may be that there is an unexpected power outage which prevents the integrator’s remote computer from properly powering OFF the GSP-1620.  In any of these types of situations, one way to get around this problem is to go through a silent resetting of the NVRAM every time the GSP-1620 is powered on.  This might take a few seconds longer, but the user does not realize the extra boot time, and just knows that he has to wait till the modem is ready before he can transact his data sessions.

One way of resetting the NVRAM upon Power_ON is to ground the reset pin (pin 25) of the GSP-1620 while the modem is being initially powered, and then release the reset pin.  Using this procedure, the GSP-1620 resets its NVRAM upon every Power_ON sequence.  Another way to reset the NVRAM is to Power_ON the GSP-1620, deassert all DTR signals so that the GSP-1620 shuts down gracefully, follow the above_described Power_OFF protocol, and then re-assert one of the DTRs and follow the above_described Power_ON protocol before proceeding with trying to register the modem on the system.

Written by Joseph Crowley

September 18, 2017 at 3:52 am

Posted in GSP-1620

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