Sad Story

Al Johnson openmoko at
Sat Dec 13 18:55:32 CET 2008

On Saturday 13 December 2008, Karthik Kumar wrote:
> On Sat, Dec 13, 2008 at 9:53 PM, Stefan Monnier
> <monnier at> wrote:
> >> There are still hardware problems that exist with almost every
> >> freerunner out there (GPS signal levels, for one).  I would like to
> >> see them fixed by Openmoko, Inc.
> The kernel fix for GPS is a mere quirk. Ideally it should get fixed in
> hardware. I am sure that Openmoko's GTA03 changes include a
> replacement of the existing u-blox. Is Openmoko considering fixing the
> GPS?

You appear to be misinformed. The kernel fix enables the hardware SD drive 
strength control. This is _not_ a mere quirk - reducing EMI is one of the 
reasons hardware manufacturers include such a hardware feature. The early 
kernels had the drive strength hardcoded to the highest value which was 
higher than necessary in this hardware configuration, and caused interference 
problems. This was a software bug, and was fixed in later kernels by setting 
a lower default drive strength that is appropriate to the hardware 
implementation. This reduces EMI to the point that the ublox gps module 
performs to specification with the internal antenna even during writes to the 
SD, and generally outperforms my Garmin Geko 201.

You may have been thinking of the earlier kernel fix which disabled the SD 
clock when it wasn't necessary, where previously it had been running 
continuously. This also reduced EMI when no data transfers were happening, 
but should be employed to reduce power consumption anyway.

Both fixes are exposed as parameters in sysfs, so you can adjust the drive 
strength, and enable the clock permanently if you wish. There is a script in 
the wiki that will cycle through the possible settings recording TTFF so you 
can see the effects for yourself. Note that you need to disable any gps 
daemons before running it, and it will take a long time too run.

When both are unassisted it also gets a fix faster and more reliably than a 
friend's N95. The N95 uses a different form of assistance, and when assisted 
it can get a fix faster than the GTA02, and in locations the GTA02 can't. I 
have yet to try the GTA02 assisted.

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