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RTOS/CC1350: Timer frequency question on CC1350

Nathan Siegel
Genius 10980 points

Part Number: CC1350
Other Parts Discussed in Thread: SYSBIOS

Tool/software: TI-RTOS

Hi,

We are running the BLE stack on the CC1350 LaunchPad and we have it connected to an external ADC via SPI. We need to achieve 20 kHz sampling (50 us). We tried to implement this using a periodic timer via the sysbios clock driver, but we were not able to achieve that high of a frequency.

static void radioSyncTxClockCallback(UArg a0)

{

    GPIO_toggleDio(24);

}

We used a callback as shown above, and we are seeing that pin get toggled as shown above. Is there a way to implement this where we can get a consistent 20 kHz timing?

  • 0
    TI__Genius 14860 points

    Hi,

    20 kHz sample-rate is a lot. What is the amount of data that has to be transferred every 50 µs and what SPI clock speed are you using? Within 50µs, the CC1350 can only execute 2400 instructions. In reality, the number is less because of bus accesses. 

    My gut feeling is that you will not be able to achieve what you want. The current SPI driver also has a lot of overhead as it configures the DMA first and does a lot of setup work. And then you have the BLE stack which, I guess, requires to run with high-priority as well.

  • 0 in reply to Richard W.
    TI__Genius 10980 points
    Hi,

    I am transferring 16 bits every 50 us, and using a SPI bit rate of 12 Mbps.

    Could you give a best estimate of the max sampling frequency we should be able to achieve using RTOS timer and the SPI driver?

    Thank you,
    Nathan