Since the RX FIFO queue is something like 128 bytes, it would take a few packets to make it overflow. Page 33 of the CC2420 datasheet explains:
The RXFIFO can only contain a maximum of 128 bytes at a given time. This may be divided between multiple frames, as long as the total number of bytes is 128 or less. If an overflow occurs in the RXFIFO, this is signalled to the microcontroller by setting the FIFO pin low while the FIFOP pin is high. Data already in the RXFIFO will not be affected by the overflow, i.e. frames already received may be read out. A SFLUSHRX command strobe is required after a RXFIFO overflow to enable reception of new data. Note that the SFLUSHRX command strobe should be issued twice to ensure that the SFD pin goes back to its idle state. And that's what the driver does. -David _____ From: roberto pagliari [mailto:[EMAIL PROTECTED] Sent: Monday, September 24, 2007 10:50 PM To: David Moss Cc: tinyos-help@millennium.berkeley.edu Subject: Re: [Tinyos-help] CC2420 packet delivery Hi David, if a STXON command strobe is issued, during the receiption of a packet I'm sure the radio will transmit it. If the received bytes stay into the RXFIFO queue (is it true?) and sometime later the radio receives another packet, that would overflow, since the expected number of bytes was the previous one. What happens in that case? Does the radio flushes the RXFIFO queue? thanks On 9/18/07, David Moss <[EMAIL PROTECTED]> wrote: Never explicitly tried it before with the intention of noting the results, but your node should transmit, leaving the RXFIFO turned to garbage and filtered out naturally by the receive methods (i.e. checking for a proper length byte and CRC). I could be wrong, but note that having two transmitters next to each other without using clear channel assessments leaves them both transmitting and rarely receiving clean packets. If the length byte is within bounds, then the radio stack can safely download the packet and check the CRC byte regardless of what happened. If the length byte in the RX FIFO is not within bounds (smaller than expected, or larger than the RX FIFO size) then the RX FIFO certainly needs to be flushed. -David _____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of roberto pagliari Sent: Tuesday, September 18, 2007 4:43 PM To: tinyos-help@Millennium.Berkeley.EDU Subject: [Tinyos-help] CC2420 packet delivery Hi All, does anyone know what happen if, during the receiption of a packet, a STXON (not STXONCCA) strobe command from the microcontroller is issued? Does the radiochip turn the circuit to the transmitter? If so, should I flush the RXFIFO queue? many thanks, Roberto
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