[LinuxPPS] Using GPS for automotive applications

[Rodolfo Giometti]

On Sun, Apr 06, 2008 at 10:11:56AM -0400, Neal Probert wrote:
> VII
> ---
> This is a US-DOT funded project with involvement from most of the 
> automotive companies and a dozen other suppliers/vendors.  There are a 
> number of experimental public, safety and private applications being 
> developed.
> 
>     http://www.its.dot.gov/vii/

Thanks for the URL, I'll put it on the LinuxPPS's wiki. :)

> Most of work we're doing is still research and development, working to 
> get the cost of GPS units down and find ways to improve accuracy and 
> precision in the moving vehicle.
> 
> DSRC is basically a WiFi link at 5.9Ghz.  We're using Linux because it's 
> a hell of a lot cheaper and easier to add a new network protocol stack 
> to an open source operating system.

I just looked around in the site but I didn't see any reference to
Linux nor PPS... maybe exists some technical reference page? :)

> 
> The VII testing in taking place in Farmington Hills/Novi in the Detroit, 
> Michigan area.  Another test area is in California.
> 
> GPS
> ---
> DoD has removed all dilution from the satellite signals.  There is a new 
> generation of satellites (block III) going up in the next decade or so 
> that drastically improves the accuracy and precision.  That implies new 
> GPS receivers, of course.
> 
> The DGPS signal is sent from a local DGPS base station to the traffic 
> lights which is broadcast to the test vehicles.  At this point in time, 
> it's not a significant improvement.  We're probably looking at using 
> each traffic light as a virtual reference station in the future.
> 
> Automotive
> ----------
> Most automotive GPSes use the speed input from the vehicle, so they can 
> do a little dead reckoning.  Most consumer grade GPSes are often based 
> on the ARM chipset, so only support single precision floating point 
> math.  So SiRF and u-Blox, even with corrections, aren't good enough.
> 
> For VII, we're doing 100 msec extrapolations based on vehicle speed, 
> acceleration and yaw available from the vehicle's CAN bus.  A lot of 
> information is available from modern vehicles because it's used for 
> anti-lock brakes, traction control systems, vehicle dynamics control, ...
> 
> Some folks are adding an IMU which helps in cases where you need dead 
> reckoning in the urban canyon.  Spend a little more money we can get 
> higher quality (a lot more money in the case of the Applanix) positioning.
> 
> Linux Kernel
> ------------
> The PPS integration is important for DSRC radio synchronization and 
> keeping the OS clock in sync.
> 
> So I'm looking at waiting on the 2.6.26 kernel, so it looks like I'll 
> need to be patching the latest Ubuntu kernels to get what I need.

Please, try patch ntp-pps-2.6.24-ter.diff.

> So, yes, it would be very handy and helpful to get this integrated into 
> the kernel as soon as possible.  It would be a huge win for Linux.

I'm working on it. ;)

> PPS Interface
> -------------
> The simplest way I can see interfacing the PPS is through a MAX232 chip 
> into the serial port's DCD input.  Right?

Why do you need connecting the PPS signal to the DCD pin? Can't you
use a dedicated CPU's GPIO?

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti at enneenne.com
Linux Device Driver                             giometti at linux.it
Embedded Systems                     phone:	+39 349 2432127
UNIX programming                     skype:     rodolfo.giometti