XMac: at some slotTime values, the number of successfully sent packets drop

[adamgeorge309]

Chart from the Sensornetwork showcase:

The graph is not smooth.

Here is what happens:

• A sensor sends preambles
• The gateway wakes up and sends ack
• The sensor node would send the data but another sensor node starts sending preambles and the original sensor node's mac is stuck in SEND mode and doesn't do anything from this point
• Eventually all sensor nodes get into this state and the number of successfully sent packets is low ~5 packets

[ZoltanBojthe]

Bug in XMAC state machine

[ZoltanBojthe]

And configuration error: headerLength = 24B , bitrate=19200bps with checkInterval=0.01s not a valid configuration. The checkInterval needed for send_preamble+rcv_ack time. But the 24B header with 19200bps is 0.01s in itself.