Mayur -
Not sure what the difference is, since PacketLink uses PacketAcknowledgements to setup and test for acks. The PacketLink layer simply retries messages when they don't get through, and is completely optional. If you're only interested in the PacketAcknowledgement layer, then not compiling in the PacketLink functionality is the way to go, saving you memory footprint. _____ From: Mayur Maheshwari [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 12, 2007 9:38 AM To: David Moss Cc: tinyos-help@millennium.berkeley.edu Subject: Re: PacketLink/RadioBackoff unexpected behavior Hi David, Thanks once again for your inputs. I understand that there is SPI contention problem. However, I installed "TestPacketLink" app which does not use flash at all and still the acks are not received. Moreover, when I install the TestAcks app (which uses PacketAcknowledgement) the transmitter starts receiving acknowledgements. Also, what is the advantage of using PacketLink over PacketAcknowledgements except for the application level retries/delays in the latter? Any ideas? Secondly, it is fine till the transmitting mote with small backoff is able to get its packets first to the receiver. This way the receiver should be able to send the acknowledgement first to the mote with small backoff so that it again send other packets early. Mayur, The problem with PacketLink is the fact that your acknowledgements are being dropped. The wasDelivered() command simply forwards to PacketAcknowledgements.wasAcked(). This could be caused by several things, but since you're probably using flash, that's probably the reason why. The SPI bus arbitration prevents the radio from handling acknowledgements correctly while the flash is in use. This is a known issue, and I have a fix going on my machine but don't have it ready for release. The fix involves forcing the CC2420 to hang onto the SPI bus while it is waiting for an acknowledgement. On your second issue, the backoffs should be in units of microseconds. Again, the CC2420 has to acquire the SPI bus before it can read a packet from the chip and this process, combined with actually reading bytes over SPI, could potentially last longer than the backoffs you have specified. In other words, the SPI bus will probably remain active and read both packets in simultaneously because there's not a big enough time delay between the two transmissions. Statically specifying your backoff period like you have should force mote A to get its packet through first, but you probably won't be able to detect which transmitter transmitted first unless you check both packets' source addresses. Hope that helps, -David _____ From: Mayur Maheshwari [mailto: [EMAIL PROTECTED] Sent: Monday, June 11, 2007 4:29 AM To: David Moss; tinyos-help@millennium.berkeley.edu Subject: PacketLink/RadioBackoff unexpected behavior Hi David, It was nice of you that you helped me with the information on blackbook. However there seems to be problem galore ;) 1. PacketLink I tried using the PacketLink interface in one of my apps and it fails to receive the acks. Previously, I was using the PacketAcknowledgements interface and it was running absolutely fine. However, it seems that the wasDelivered(msg) event in PacketLink returns FALSE all the time. I tried testing the app TestPacketLink in \tinyos-2.x\apps\tests\cc2420\TestPacketLink and the acks were never received and the Transmitter toggled led0 every 2 secs. Again, I tested the TestAcks in \tinyos- 2.x\apps\tests\cc2420\TestAcks which uses the interface PacketAcknowledgements and this does gives positive results. 2. RadioBackoff I tested radiobackoff by having events in an app installed on two motes(A and B). I initialised the Initial Backoff times as 11 and 300 for both the motes resp. Now, I installed another app on another mote C which broadcasts and when A and B receive this broadcast they unicast their messages to C. It was expected that the message from mote B should be delayed by ~ 300 ms but I noted both the messages getting into C simultaneously. To be more clear on this aspect I recorded the events in a video and played at slower speeds but to no avail. The Leds on the mote C blink in 2~3 ms delay and I could not determine which packet went first. Would you be able to share some code in this regard. Thank you once again for all the help. Mayur -- Mayur Maheshwari( <mailto:[EMAIL PROTECTED]> [EMAIL PROTECTED]) "Karmanye Vadhikaraste Ma Phaleshu Kadachana, Ma Karma Phala Hetur Bhurmatey Sangostva Akarmani" -- Mayur Maheshwari([EMAIL PROTECTED]) "Karmanye Vadhikaraste Ma Phaleshu Kadachana, Ma Karma Phala Hetur Bhurmatey Sangostva Akarmani"
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