Table of Contents

Synchronization Clock Protocol (1.0)

Introduction

The Harp Synchronization Clock is a dedicated bus that disseminates the current time to/across Harp devices. It is a serial communication protocol that relays the time information. The last byte in each message can be used as a trigger, and allows a Device`` to align itself with the current Harp` time.

Serial configuration

  • The Baud rate used is 100kbps;

  • The last byte starts exactly 672 us before the elapse of the current second (e.g.:)

    "SynchClockOscilloscope

  • The packet is composed of 6 bytes (header[2] and timestamp_s[4]):

    • header[2] = {0xAA, 0xAF)
    • timestamp_s is of type U32, little-endian, and contains the current second.

Important

To avoid unexpected behaviors, only one bit at a time should be written to register R_RESET_DEV.

Example code

Example of a microcontroller C code:


ISR(TCD0_OVF_vect, ISR_NAKED)
    {
        if ((*timestamp_byte0 == 0xAA) && (*timestamp_byte1 == 0xAF)) reti();
        if ((*timestamp_byte1 == 0xAA) && (*timestamp_byte2 == 0xAF)) reti();
        if ((*timestamp_byte2 == 0xAA) && (*timestamp_byte3 == 0xAF)) reti();

        switch (timestamp_tx_counter)
        {
            case 1:
                USARTD1_DATA = 0xAA;
                break;
            case 2:
                USARTD1_DATA = 0xAF;
                break;
            case 4:
                USARTD1_DATA = *timestamp_byte0;
                break;
            case 6:
                USARTD1_DATA = *timestamp_byte1;
                break;
            case 7:
                USARTD1_DATA = *timestamp_byte2;
                break;
            case 1998:
                USARTD1_DATA = *timestamp_byte3;
                break;
        }
    }

Physical connection

The physical connection is made by a simple audio cable. In the same folder of this file, you can find an example of the sender and the receiver. The connector used is from Switchcraft Inc. with PartNo. 35RASMT2BHNTRX.

Release Notes

  • v1.0

    • First version.

  • v1.1.0

    • Refactor documentation to markdown format.
    • Minor typo corrections.
    • Improve clarity of some sections.
    • Adopt semantic versioning.

  • v1.1.1

    • Remove table of contents to avoid redundancy with doc generators.
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