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CC1125 transmits in FSTXON State

Johannes Wechsler
Prodigy 80 points
Other Parts Discussed in Thread: CC1125

Hello,


I'm currently working on a project using the CC1125. I want to transmit short data packages (upto 50bit) without any preamble or snyc word. I want to utilize the FSTXON state to ensure the frequency synthesizer is settled and allow me to send the data at a percise moment.


The flow I follow is as follows:

  1. Startup
  2. Setup CC1125 Registers (frequency, symbol rate ... etc.)
  3. Calibrate manually (according to errata)
  4. Load Packet specific settings to CC1125 (txpower, length ...)
  5. Flush TX-Queue
  6. Fill TX-Queue with new data
  7. Goto State: FSTXON
  8. Wait until timer issues Interrupt
  9. Goto State: TX
  10. When Finished: Goto State: Idle (or PowerDown)
  11. Restart from step 4

As long as I reset the CC1125 after the succesful transmit (by going to Power-Down in step 10), the CC1125 does not transmit anything until the TX strobe is issued. But when I go to Idle in step 10, the chip immediatly starts transmitting (something, I can't say what exactly) once the FSTXON strobe is issued for the next packet

This does not occur with the first package, as the chip has been "reset" before starting the flow.

To illustrate, I attached a picture:

  • On the rising blue edge, the Queue is filled and the FSTXON strobe is issued.
  • On the falling blue ednge, the TX strobe is issued
  • The time in FSTXON in the first package is longer because the delay is optimized over time, but it does not make a difference to adjust this manually, the first package always works
  • All othe packages later look exactly as the second one


Things I tried so far without any success:

  • Compare all registers, basic and extended, they are identical in the first and second package
  • Go to RX or IDLE right after successful transmit
  • Check FIFO-Flush
  • Add TX-FIFO-Flush right after successful transmission
  • Check states
  • ...

Maybe someone ran into the same issue and can provide any help.

Thanks,

best regards,

Johannes

  • 0
    TI__Guru**** 317180 points

    - In your figure, what is the green and the pink waveforms?

    - The radio should only start sending when in Tx which is reached by a STX strobe. When you issue a SFSTXON strobe you will not be in Tx. When you issue this strobe which value do you read back from MARC state?

  • 0 in reply to TER
    Prodigy 80 points

    The pink line is a bit that is set high when the STX Strobe is issued and set back to low, when the interrupt over GPIO2 arrives, that the transmit is done. When the blue line is on the falling edge, the pink one rises. You can't see that here due to the insufficient resolution of the image.


    The greenish-yellow line is the RF Signal

    When I send a SNOP strobe, before the transmit, where the radio is already busy (see the yellow line) the returned state is FSTXON.