[Discuss-gnuradio] RFID data packet

[Andrea Farulli]

I have to develop a system for RFID operating in the 433 MHz frequency
band (ISO 18000-7) transmission with the GNU radio python framework.
I succeded transmitting a simple message with bfsk modulation using the
gr.cpfsk_bc block with the proper parameter (carrier frequency,
frequency deviation, bitrate).
I'm trying now to implement the data link layer according to which data
is sent in packet format, a packet is comprised of a preamble, data
bytes and a final logic low period. Data bytes are sent in Manchester
code format.
The problem is: the length of the preamble pulses and the lenght of the
data bit period are different, but I can only specify one bitrate in the
gr.cpfsk_bc block (well not exactly the bitrate, the modulation index
and the number of output samples per input bit, which depend on the
bitrate).
Have I to vary the bitrate according to which part of the packet I am
transmitting? Or have I to choose one bitrate and to vary the sequence
of symbol to reproduce the proper period length?
Are there any helper function int the framework to do the job? What the
simple_framer block exactly does, are there other blocks dealing with
framing.

Andrea