Timer for generating 1us tick

[SShid]

I'm using STM32F108RG on 48MHz clock configuration.

I need to generate a 1 micrososeconds timer tick on it, for driving an output pin interfaced with a 3rd party device. Using PWM is not an option available.

I tried configuring TIM3 with following parameters:

Clock: Internal (48MHz)

Prescaler: 47 (48 - 1)

Counter Mode: Up

Counter Period (Auto-Reload Register -16 bit): 1

Internal Clock Division: No Division

Auto-reload preload: Disabled

With these settings, the closest I can reach is 6.8us.

I was able to generate 10us with the above settings with Counter Period set to 10,

but it doesn't seem to go below 6.8us.

I also tried TIM1 for the same purpose, but got the same observations.

Is that a limitation of the device, or do I need to perform any additional steps?

[Tesla DeLorean]

Don't interrupt at these speeds you will saturate the processor.

Have a TIM count at 1 MHz, and spin on TIM->CNT advancing a required amount.

Consider also DWT_CYCCNT​

[TDK]

You could use SPI with a 1MHz clock to output an arbitrary signal. Calling an interrupt at 1MHz isn't going to pan out well. It'll take more than 48 ticks for the ISR to complete.

[SShid]

Thanks for the response, clive1

I'm a complete noob on STM32 platform (otherwise wouldn't have had posted such queries)

So what exactly do you mean by "spin on TIM->CNT"?

Also, what is 'DWT_CYCCNT'?

I gave it a search in the HAL library thinking that it's some sort of peripheral register,

but couldn't find it.

Apologies for asking for more help on this.

[SShid]

That would have been a great idea.

Thanks for the response, TDK; but I don't think I have enough SPI peripherals left on my application.

[Tesla DeLorean]

If terms are unfamiliar stick them into Google or the search here, should be preexisting examples and postings.

With TIM3, prescale 47, period 0xFFFF (maximal)

void delay_us(uint16_t us)

{

uint16_t start = TIM3->CNT;

while((TIM3->CNT - start) < us) {};

}

For finer granularity, let the TIM clock faster, use a 32-bit TIM where available

[Tesla DeLorean]

//****************************************************************************
 
volatile unsigned int *DWT_CYCCNT   = (volatile unsigned int *)0xE0001004; //address of the register
volatile unsigned int *DWT_CONTROL  = (volatile unsigned int *)0xE0001000; //address of the register
volatile unsigned int *DWT_LAR      = (volatile unsigned int *)0xE0001FB0; //address of the register
volatile unsigned int *SCB_DEMCR    = (volatile unsigned int *)0xE000EDFC; //address of the register
 
//****************************************************************************
 
void EnableTiming(void)
{
  *SCB_DEMCR |= 0x01000000;
  *DWT_LAR = 0xC5ACCE55; // enable access (required on Cortex-M7)
  *DWT_CYCCNT = 0; // reset the counter
  *DWT_CONTROL |= 1 ; // enable the counter
}
 
//****************************************************************************
 
void Delay(uint32_t cycles) // Based on SystemCoreClock, at 48 MHz, 48 cycles is 1us, 48000 cycles is 1ms
{
  uint32_t start = *DWT_CYCCNT;
 
  while((*DWT_CYCCNT - start) < cycles);
} // sourcer32@gmail.com
 
//****************************************************************************

[S.Ma]

interrupts at 10kHz or higher is the symptom of danger. use hw assist as much as possible. if you have a spare timer pin channel or spi mosi, short it with the one you want to send a pulse pattern by dma if needed. no spare pin? new board design?

[Tesla DeLorean]

Indeed modulating patterns with fixed timing requirements can be done with TIM+DMA+GPIO more effectively than using timing loops eating all processor resources.

Consider also logic or CPLDs for hardware orientated problems.

[Tesla DeLorean]

With hard software timing loops you're going to run out of bandwidth for your application pretty quickly