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Fastest way to toggle GPIO with DSP/BIOS on OMAPL138 C67xx Core

Christian Rückl
Intellectual 340 points
Other Parts Discussed in Thread: OMAPL138

Hi,

I'm using the OMAPL138 processor (CLOCK=300 MHz) and startet with a DSP/BIOS (5.41.11.38) applikation. I also implementet the PSP-GPIO-Driver (1.30.01) . But when control the pinvalue, as shown in the PSP-example, and put the following code in a while-loop:

pinCmdArg.pin   = GPIO8_14_PIN;

pinCmdArg.value = 0;

Gpio_setPinVal(gpio0, &pinCmdArg);

pinCmdArg.pin   = GPIO8_14_PIN;

pinCmdArg.value = 1;

Gpio_setPinVal(gpio0, &pinCmdArg);

 

The measured frequency on this pin is at 520 kHz. No parallel Task is running. The Symbol "PSP_DISABLE_INPUT_PARAMETER_CHECK" is defined, performance the same than without this defined symbol. To get a higher toggle frequence, I extracted the following lines from the PSP-Driver and put it also in a while loop:

gpioBaseAddress->BANK[4].SET_DATA = (1u<<14);

gpioBaseAddress->BANK[4].CLR_DATA = (1u<<14);

The measured frequency on the pin is now 8.222 MHz but in my mind still slow.

 

Can anybody suggest me a way how to increase the speed of this procedure?

 

Thanks a lot,

Christian

 

 

  • 0
    Guru 26430 points

    You could putting as much as you can into registers and avoid any repetitive address calculations. Something like:

    void toggle(int bank, int gpio, int n)
    {
      register int nr = n;
      register volatile Uint32 *pSET = &gpioBaseAddress->BANK[bank].SET_DATA;
      register volatile Uint32 *pCLR = &gpioBaseAddress->BANK[bank].CLR_DATA;
      register Uint32 mask = 1u<<gpio;
      do
      {
        *pSET = mask;
        *pCLR = mask;
      }
      while(--nr);
    }

    The compiler probably already produces the same code in release mode.

  • 0 in reply to Norman Wong
    Intellectual 340 points

    Thanks for your answer.

    in your version, i'm able now to let the pin toggle with 12.5 MHz.

    Is this the highest reachable frequency?

     

     

  • 0 in reply to Christian Rückl
    Guru 26430 points

    There are few posts about GPIO speed in this forum. Here's a few:

    http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/127628.aspx
    http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/135631.aspx

    You could try hand coding in assembler with C67xx specfic opcodes. Or in C if the intrinsic library has the opcode your want. I have doubts you can get much faster as the GPIO controller itself has large delays. Unrolling the loop and removing the loop counter test for a fixed number of cycles might be faster as well. All depends on the instruction cache and pipeline. Instruction cache favours tight loops. Pipeline favours unrolled loops. I don't know enough to say which is better.