[Tinyos-devel] Testing FTSP

[Miklos Maroti]

Brano,

>> timestamp is correct? I think the timestamp should be set only if
>> there is a single timestamp in the timestamp queue AND a the RXFIFO is
>> empty (that is this was the only message timestamped).
>
> i only timestamp message if the timestamp queue size is 1, otherwise i clear
> the timestamp and reset the queue. take a look at CC2420ReceiverP and
> CC2420TransmitP in contrib/stanford-lgl/apps/tests/TestPacketTimeStamp

I think that is bad logic! You should NOT clear the timestamp
queue,because then a new message (C) arrives in the RXFIFO and then
the timestamp queue will contain a single timestamp and then your next
downloaded message (B) will be associated with the timestamp of the
latest message (C)! This is BAD! I think you should kill the timestamp
queue completely, and keep only the timestamp_size which would be
maintained as before. Only when you switch from 0 to 1, that is when
you want to timestamp the message. For example you could do the
following (I do not guarantee that it even compiles):

uint32_t m_timestamp;
uint8_t m_timestamp_count;

async command void CC2420Receive.sfd( uint32_t time ) {
  if( ++m_timestamp_count == 1 )
    m_timestamp = time;
  else if( m_timestamp_count == 2 )
    m_timestamp_count = 3;
}

async command void CC2420Receive.sfd_dropped() {
  if ( m_timestamp_count > 3 )
    --m_timestamp_count;
  else
    m_timestamp_count = 0;
}

async event void RXFIFO.readDone ...
      if ( m_timestamp_count == 1 && rxFrameLength > 10 )
        call PacketTimeStamp.set(m_p_rx_buf, m_timestamp);
      else
        call PacketTimeStamp.clear(m_p_rx_buf);

      if ( m_timestamp_count > 3 )
        --m_timestamp_count;
      else
        m_timestamp_count = 0;

  void reset_state() {
    m_bytes_left = RXFIFO_SIZE;
    atomic receivingPacket = FALSE;
    m_timestamp_count = 0;
    m_missed_packets = 0;
  }

> the first two fixes didn't help (though i observed decreased frequency of
> errors). after adding the last fix, i wasn't able to see these errors on
> micaZ.

Good news.

> clearly, there is a problem in how the timestamp is converted from 16 to 32
> bits. this is done in CC2420TransmitP.nc (the modified file in
> TestPacketTimeStamp dir):
>
> 239  inline uint32_t time16to32(uint16_t time, uint32_t recent_time)
> 240  {
> 241    if ((recent_time&0xFFFF)<time)
> 242      return ((recent_time-0x10000UL)&0xFFFF0000UL)|time;
> 243    else
> 244      return (recent_time&0xFFFF0000UL)|time;
> 245  }

Replace it with the following code adopted from the RF230 driver:

inline uint32_t time16to32(uint16_t time, uint32_t recent_time)
{
  return recent_time + ((int16_t)time - (int16_t)receint_time);
}

> which is called from
> 260  async event void CaptureSFD.captured( uint16_t time ) {
> 261    uint32_t time32 = time16to32(time, call BackoffTimer.getNow());

> clearly CaptureSFD.captured() is async, so line 261 should be atomic. do you see any
> other problems?

Why should it? GetNow must be internally atomic, and then you are
working on local variables only, so there is no race here.

Miklos