How to alter GPIO pin's toggle frequency on MSP432

Henry Bishop

Hi all,

I just got the MSP432 and have been trying to use the 48 MHz clock as the source for which the GPIO pins could toggle on and off as an output, but have been unsuccessful even though the sources show that they are running at 48 MHz. The code I have now to change the clock freqs is:

WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer

CSKEY = CSKEY_VAL;
CSCTL0 = DCORSEL_5;
CSCTL1 = SELS_3 + SELM_3 + DIVS_0 + DIVM_0;
CSCTL2 = HFXTFREQ_6;
CSKEY = 0;

//Outputs signals from MCLK, SMCLK, and HSMCLK
P7DIR |= BIT0;
P7SEL0 |= BIT0;
P7SEL1 &= ~BIT0;
P4DIR |= BIT3 | BIT4;
P4SEL0 |=BIT3 | BIT4;
P4SEL1 &= ~(BIT3 | BIT4);


P1DIR |= BIT5;

while(1) {   // Want to maximize toggle frequency
P1OUT |= BIT5;
P1OUT &= ~BIT5;
P1OUT |= BIT5;
P1OUT &= ~BIT5;
}

Any thoughts as to how this should be done? I just need these pins to toggle as fast as possible.

Thanks!

over 8 years ago

0 Michael Arriete56 over 8 years ago

TI__Expert 3295 points

Hi Henry,

I'll be happy to look into this for you and will have an answer as soon as possible.

Regards,
Michael Arriete

0 Dennis Eichmann over 8 years ago

Guru 74080 points

P1OUT = BIT5;
P1OUT = 0x00;

0 Michael Arriete56 over 8 years ago

TI__Expert 3295 points

Henry,

Did the post by Dennis answer your question? Please let us know so we can close this thread.

Regards,
Michael Arriete

0 Henry Bishop over 8 years ago in reply to Michael Arriete56

Prodigy 150 points

This did not but I am instead trying to utilize the on-board SPI module to do what I need.

0 Dennis Eichmann over 8 years ago in reply to Henry Bishop

Guru 74080 points

So the direct assignment of a value to the port isn't faster than the RMW operation?

Henry Bishop said:
instead trying to utilize the on-board SPI module to do what I need

Could you please explain your final application? I do not understand it. If you want to toggle an output pin as fast as possible, then why not simply take the HSMCLK output at 48MHz?

Dennis

0 Michael Arriete56 over 8 years ago in reply to Henry Bishop

TI__Expert 3295 points

Henry,

I have to agree with Dennis. For the quickest toggling of the pin in code, that should have done it. Please provide some more information on what you're trying to achieve as the final application.

Thanks,
Michael Arriete

0 Henry Bishop over 8 years ago in reply to Michael Arriete56

Prodigy 150 points

Sure so the end goal is to perform SPI operation as fast as I can on a time critical system with GPIO pins in software (or in hardware with one of the eUSCI modules). In this case, I was trying to control the GPIO pins as fast as possible by using the 48 MHz clock. And yes by outputting the clock signal itself, it will get the fastest signal possible, but I want to be able to control the GPIO pins with comparable speed. With the clock signal, I am stuck with just that. Though when I set SMCLK and MCLK to source from the 48 MHz crystal the GPIO pins only seem to respond at around 1.5 MHz at their fastest.

And I just tried working with the eUSCI module and it seems like it can send out a byte somewhat quickly for my needs (5 MHz), but has a long delay I believe to be associated with waiting for the transmit buffer interrupt to fire and then reload a new value into the transmit buffer.

0 Dennis Eichmann over 8 years ago in reply to Henry Bishop

Guru 74080 points

SPI with GPIOs will be much slower because of the large overhead. Use the USCI module in combination with the DMA controller that fills the TX buffer without interrupt.

0 Henry Bishop over 8 years ago in reply to Dennis Eichmann

Prodigy 150 points

Can you give me a brief overview of what the DMA is/does?

0 Dennis Eichmann over 8 years ago in reply to Henry Bishop

Guru 74080 points

It moves data between memory and peripherals in the background without CPU intervention and therefore needs almost no processing power which makes it very fast. The user's guide has a complete chapter about it.

0 Henry Bishop over 8 years ago in reply to Dennis Eichmann

Prodigy 150 points

Great thanks Dennis I'll take a look at that.

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How to alter GPIO pin's toggle frequency on MSP432