Hello all,
I have a problem on microsecond precision timestamps. I am using CC24 radio
chip and MSP430 microcontroller. As far as I understood, the packets are
timestamped at CC2420ReceiveP and CC2420TransmitP files.
/***************** CC2420Receive Commands ****************/
/**
* Start frame delimiter signifies the beginning/end of a packet
* See the CC2420 datasheet for details.
*/
async command void CC2420Receive.sfd( uint32_t *time* ) {
if ( m_timestamp_size < TIMESTAMP_QUEUE_SIZE ) {
uint8_t tail = ( ( m_timestamp_head + m_timestamp_size ) %
TIMESTAMP_QUEUE_SIZE );
*m_timestamp_queue[ tail ] = time**;*
m_timestamp_size++;
}
}
async event void CaptureSFD.captured( uint16_t time ) {
uint32_t time32;
uint8_t sfd_state = 0;
atomic {
* time32 = getTime32(time);*
switch( m_state ) {
case S_SFD:
m_state = S_EFD;
sfdHigh = TRUE;
// in case we got stuck in the receive SFD interrupts, we can reset
// the state here since we know that we are not receiving anymore
m_receiving = FALSE;
call CaptureSFD.captureFallingEdge();
call PacketTimeStamp.set(m_msg, time32);
if (call PacketTimeSyncOffset.isSet(m_msg)) {
uint8_t absOffset =
sizeof(message_header_t)-sizeof(cc2420_header_t)+call
PacketTimeSyncOffset.get(m_msg);
timesync_radio_t *timesync = (timesync_radio_t
*)((nx_uint8_t*)m_msg+absOffset);
// set timesync event time as the offset between the event time
and the SFD interrupt time (TEP 133)
**timesync -= time32;*
call CSN.clr();
call TXFIFO_RAM.write( absOffset, (uint8_t*)timesync,
sizeof(timesync_radio_t) );
call CSN.set();
//restoring the event time to the original value
*timesync += time32;
}
My problem is, as far as I understood, the "time" parameter of these
functions are all in 32 KHz. I am currently implementing a time
synchronization protocol and I need microsecond precision. Current version
of TinyOs does not have interfaces that serves microsecond timestamps in my
platform.
What are your suggestions? Is there a way to get microsecond precision?
Thanks for your helps and thanks a lot...
K. Sinan YILDIRIM
Ege University
Computer Engineering Department
İzmir, TURKEY
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