This is the latest Hoernerfranzracing-Project - as mentioned, a Laptimer for automatic acquisition/display of laptimes during a race/practice session.
We had already a first prototype with us in Val de Vienne, but there were still some hardware- and software related problems.
These have been cured, meanwhile, so I hope all goes well in Mas du Clos.
As said, the device is based on the 'Butterfly-Evaluation-Kit' from norwegian company Atmel - it contains all necessary components, so there is no need of extra circuit development/test.
Additionally, programming is relative easy via serial interface - no need for expensive programmers whatsoever.
Next advantage is the free availability of development/programming tools like
avrdude (Programming-tool,
supports several kinds of adapters/interfaces)
as well as the gcc-addon avr-libc -
of course all for Linux 
.
Now that's a point to get started from, especially the gcc-port ,
for the included demo-application which was originally developed by Atmel using their proprietary IAR C-Compiler.
An easy way to get started here is especially the so called 'state-machine' -
which saves a lot of work/coding as it provides an easy-to configure user-interface via LCD/Joystick.
The heart of the Laptimer-Software - the function for measuring the actual laptime,
was directly derived from the included real-time-clock function - see file RTC.c.
As opposed to the original, Timer2 isn't driven with prescale 1024 (which gives a 1 Hz Interrupt frequency), but without prescale.
This way an update-freq. of 1/16 Hz is obtained, which is ok for the first step,
impovement can still be done by direct usage of the counter register.
The actual measurment is then done by monitoring digital input PB2, which reads the state
of the output signal from an on-bike mounted radio-receiver, which will go to 'HIGH' state
when the vehicle passes the sender, located somewhere at the track.
As soon as that happens, the actual value of the system-time (32 bit integer value with 1/6 sec resolution) is recorded, as well as calculation of the difference to the time of the last event.
This is the actual laptime, which is then converted to a suitable format for display on the LCD.
In addition, the laptime is stored internally in a dynamic, linked list, which makes it possible to lateron recall all laptimes via Joystick, as well as send the list to a pc via serial interface, upon request.
The application-menu is available here as PDF file .
.