LAPTIMER

Firmware for wireless laptimer system. The system contains of a sender and a
receiver, both containing an RFM75 wireless module and an ATmega8u2
microcontroller.

To build the firmware one requires GNU Make, avr-gcc, avr-binutils and avr-libc
packages. Makefile is also prepared to flash the microcontrollers using avrdude
software and AVR-ISP-MK2 programmer (OLIMEX).

To build the firmware just type

        make

To flash the firmware, type either

        make program-receiver

or

        make program-sender


        SYSTEM SPECS

RF Channel:             78 (2478MHz)
TX Power:               4dBm (2.5mW)
Air data rate:          250Kbps
Number of pipes:        6
Number of transmitters: 16
Retransmission:         automatic, with acknowledgement
Reception distance:     100-125m
PC Interface:           USB, Communication Device Class
Lap buffer:             up to 32 entries (before receiver acknowledges the reception)


        LED INDICATION

Receiver LEDs:

        +---------------+---------------------------------------------------------------+
        | LED           | Function                                                      |
        +---------------+---------------------------------------------------------------+
        | Green (#1)    |                                                               |
        +---------------+---------------------------------------------------------------+
        | Yellow (#2)   | blinks 8Hz:   Failed to configure/detect Radio Module         |
        |               | constant:     Radio Module malfunction (interrupt flood)      |
        +---------------+---------------------------------------------------------------+

Transmitter LEDs:

        +---------------+-----------------------------------------------------------------------+
        | LED           | Function                                                              |
        +---------------+-----------------------------------------------------------------------+
        | Green (D4)    | single blinks:        packet transmitted                              |
        +---------------+-----------------------------------------------------------------------+
        | Yellow (D5)   | blinks 1Hz:           FIFO overflow (no ACK from receiver)            |
        |               | blinks 8Hz:           Failed to configure/detect Radio Module         |
        |               | constant:             Radio Module malfunction (interrupt flood)      |
        +---------------+-----------------------------------------------------------------------+


        RECEIVER PROTOCOL

On the receiver side USB interface is used to connect to PC for data acquision
and display. Standard Communication Device Class is implemented in the receiver
firmware, which allows for usage of the standard OS drivers for USB-serial
adapters. The USB Product ID (PID) was sublicensed from Microchip (VID 0x04D8)
and is 0xEB86.

The application protocol is a simple text form consisting of lines of data
separated by <CR><LF> combination. Each line has a form:

<key> <parameter-1> ... [parameter-n]

Once after power up, on the first USB enumeration the receiver transmits the
following line:

VER <version>

where <version> is the firmware version. This is done mainly for diagnostic
purposes.

Every time a sender is being powered, the receiver reports:

PWR <address>

where <address> is the address of the sender set by address switch, in the range
0 to 15.

Every time the sender receives a timing synchronisation signal, the receiver
prints:

LAP <address> <laptime>

where <address> is the address of the sender set by address switch and <laptime>
is the number of milliseconds elapsed from the last synchronisation signal
(passing the light gate).

For the purposes of signal quality monitoring sender can report the number of
retransmissions to the receiver, which is then reported as:

RET <address> <retr>

where <retr> is the number of retransmissions required to transmit the last
lap time.