Good news: FixNow mode can be wakenup through serial port

Daniel Willmann daniel at
Sun Mar 15 16:36:26 CET 2009


On Fri, 13 Mar 2009 18:24:49 -0700 (PDT)
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

This sounds quite promising. How was FixNow configured in that case?

> 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 think you misunderstood that post. In there Andy says that the GPS
will have no way to wake us up if it has a fix. What is possible is to
put the GPS into FixNow mode and wake it up either by sending some
serial data or by toggling the EXTINT0 pin that is routed to our SoC.

> 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."

Yeah, page 26f. also states that the receiver can be woken up via
EXTINT0 and it will compute and send a position in response.

> 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)

Would you mind publishing your code? I'm interested in integrating this
in ogpsd as well. 

Daniel Willmann
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