Hello,
Using: Tmote Sky, TinyOS 1.x, Cygwin WinXP I have two motes sampling 4 channels of the AD converter module at 200HZ. On the ADChannels a function generator is putting a sine with an offset applied. When 10 samples are collected from each channel (10 * 2 bytes * 4 channels = 80 bytes), they are packaged in a TOS_Msg and buffered in a TOS_Msg buffer. Another process with tasks is sending the TOS_Msg's from the buffer over the radio. THIS IS NOT A CIRCULAR BUFFER!! To understand my story you should understand that when using a high AD sampling frequency, the frequency with which you send packets will increase. More packets are generated! The TOS_Msg's are received by a TOSBase mote and the data is stored on the computer, for later visualization. Leds debug on the mote: greenON : TOS_Msg Buffer is overflowed. redOn: A packet could not be sent. Scenario 1: 2 motes sampling the ADChannels @ 20HZ works fine. When I visualize the sine, it looks good (Like the sine of the function generator). This is 20HZ sampling so the frequency of packets sending is low. No debug leds are lighting up. Scenario 2: 2 motes sampling the ADChannels @ 50HZ. This works fine for about 2.5 hours, after this period packets are missing from both motes. The missing packets period is about 30 minutes. After this 30 minutes it works fine again for 2.5 hours. No debug leds are lighting up. Scenario 3: 2 motes sampling the ADChannels @ 200HZ. This works fine for 1 hour, after this period packets are missing from both motes. The missing packets period is about 45 minutes. After this 45 minutes it works fine again for 1 hour. No debug leds are lighting up. Scenario 4: (WorkLoad is too much for TOSBase maybe?????????) 1 mote sampling ADChannels @ 500HZ. This works fine for the whole period. So in this scenario packet sending is done in a very high frequency, but TOSBase can handle them!!! No debug leds are lighting up. So TOSBase seems not to be the problem because it can handle one mote sampling @ 500HZ. The packet receive frequency is very high here!!!! When I increase the sampling frequency, the period where no packets are missing decreases. So the problem here is that when using two motes there is a period with packets not arriving at TOSBase (missing packets), maybe the motes are fighting then for the radio channel or something? Why is it working fine when using low frequency sampling or when using just 1 mote??? 1 mote has no opponent to fight with. These are my conclusions but I I still don't know the exact explanation for this problem. Why is there a period FOR BOTH MOTES at the same time missing packets? It is not random missing packets! I hope someone could help me out with this. Thank you Chougna
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