Hi, The payload you send with the standard TinyOS implementation (e.g. AMSenderC) is more or less directly put into a 802.15.4 packet which itself cannot have a bigger payload than 127 bytes (defined by the 802.15.4 PHY). Some bytes are used already for the active message headers (source_addr, dest_addr, ...), so that not the full 127 bytes are available e. g. on the IRIS platform I have 113 bytes left. You can find out by using the Packet.maxPayloadLength() provided by your ActiveMessageC.
TOSH_DATA_LENGTH just defines the size of the message structure message_t, but it does not tell the communication layer how much bytes to send (this is done directly by passing the len parameter to the AMSend.send(..., uint8_t len) command). Thus, setting TOSH_DATA_LENGTH to 1000 bytes won't enable the sending of 1000 byte packets using the standard AMSend implementations. Secondly, setting TOSH_DATA_LENGTH to high values means that whenever you define a message_t type variable, you use up >1000 bytes of RAM of your mote. Thats "quite a bit" on devices with very limited RAM (e. g. 8K bytes on IRIS mote). I do not think that this is advisable. Regards Andreas Manas Maheshwari schrieb: > Hi, > I am starting on tiny-os and working to build an application where my > packet payload can go from 0 to ,say, 1000 bytes. > > I understand that we need to modify the TOSH_DATA_LENGTH parameter to > make this possible. I am not able to figure out that does tiny-os would > always transmit TOSH_DATA_LENGTH ( which would not be optimal) or it > just passes this parameter and the actual payload length bytes only > ( say 30). > > Secondly are there any disadvantages of using high value for > TOSH_DATA_LENGTH, like some wasted memory(in case I am rarely > transmitting TOSH_DATA_LENGTH bytes) on the motes. > > Thanks > MM > > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > > _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
