Good news: FixNow mode can be wakenup through serial port

Yorick Moko yorickmoko at
Sun Mar 15 15:21:55 CET 2009

this seems extremely interesting,
i find it strange there is not more response to this mail
will FSO try to incoporate it?

On Sat, Mar 14, 2009 at 2:24 AM, mqy <meng.qingyou at> wrote:
> U-BLOX GPS chip ANTRAIS 4 and above can run in several power modes:
> 0: Continuous Tracking Mode, about 3.5 mA
> 1: Fix Now -- sleep mode about 130 uA
> Fix Now mode can be enabled by ubx binary message CFG-RXM. Detailed
> parameters are configured by CFG-FXN.
> One of the problem is how to activate (wake up) from sleep mode. I've read
> several message lists discussing this issue, it seems no way to wake up
> through serial port.
> I've tried make GPS chip goes into sleep mode several days ago, but can't
> wakeup it.
> Last night I found good references through google:
> 1.
> "When waking up TIM-Lx with RxD1, RxD2 from sleep- or backup state send a
> number (at least 8) of
> 0xFF characters to wake up the serial communication module otherwise the
> first bytes may get lost. To
> request a position fix a position request message must be sent via serial
> port after waking up the
> ANTARIS GPS Receiver."
> 2.
>   5.3.3 Change operation mode
> "Please add header with dummy data for any command when the GPS module is in
> sleep mode. This is required for wake-up in sleep mode. The dummy data in
> hexadecimal is “0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF”."
> I've test this with ubx binary protocol:
> 1) enable FixNow (sleep mode) by CFG-RXM, configure CFG-FXN
> 2) periodically poll NAV-POSLLH, NAV-VELNED, NAV-SVINFO. Before writing each
> poll request, write
>   unsigned char array {0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
>       0xB5,0x62,0x02,0x40,0x00,0x00,0x42,0xC8};
>   /* note:  first line: dummy data, second line: RXM-POSREQ */
>   then sleep 1 second;
> 3) toggle between "Continuous Tracking Mode" and "FixNow mode" by call
> CFG-RXM (if in FixNow mode, first write dummy data and RXM-POSREQ)
> With MON-SCHED, the average GPS CPU load in "Continuous Tracking Mode" is
> about 35%, regardless of send_rate, max nav SVs, 2d/2d nav mode. No
> performance test data for FixNow mode for now.
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