Help, what is going on ???

[JHERI]

Hi if anyone can help it will be very much appreciated

Yet another strange issue

so I have my stlink v2 debugger set up with Rowley crossstudio

everything works fine when debugging and running my code from the ide on my nucleo st32f446RE board, yet when I exit the ide and power down and re power, my target board does not run correctly as it did when debugging.

I have track the code down to where it is hanging and it is here

 
#pragma GCC push_options
#pragma GCC optimize ("O3")
 
void delayUS_DWT(uint32_t us) {
	 volatile uint32_t cycles = ( SystemCoreClock / 1000000L)*us;
	 volatile uint32_t start = DWT->CYCCNT;
	do  {
	} while( DWT->CYCCNT - start < cycles);
}
#pragma GCC pop_options

it get stuck in this do while loop i believe ???

I use this code to generate a short us timer

can anyone please tell me why everything works fine when debugging in the rowley ide

yet when I power down and re power it hangs in this code ???

If I REM the above routine out, my board works fine, but without my short timer

thanks in advance for any help

[Tesla DeLorean]

The debugger enables the hardware, you apparently do not

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 CycleCounter_Configuration(void)
{
  *SCB_DEMCR |= 0x01000000;
  *DWT_LAR = 0xC5ACCE55; // unlock CM7
  *DWT_CYCCNT = 0; // reset the counter
  *DWT_CONTROL |= 1 ; // enable the counter
}

[Tesla DeLorean]

More happy fluffy version

  CoreDebug->DEMCR |= 0x01000000; // TRCENA
  DWT->LAR = 0xC5ACCE55; // unlock
  DWT->CYCCNT = 0; // reset the counter
  DWT->CTRL |= 1 ; // enable the counter

[JHERI]

Hey thank you

I simply wanted a way to count in micro seconds without using a timer and interrupts I don't think interrupts for microseconds is a good approach as to much time is taken servicing very fast interrupts. so I found this code on the web

Is this ok to use for micro second timers ???

I am still not really sure what is going on but I have added a routine with this in it

  CoreDebug->DEMCR |= 0x01000000; // TRCENA
  DWT->LAR = 0xC5ACCE55; // unlock
  DWT->CYCCNT = 0; // reset the counter
  DWT->CTRL |= 1 ; // enable the counter

I had to remove

DWT->LAR = 0xC5ACCE55; // unlock

as the compiler was complaining but now I switch off out of the debugger and yes, the board works and does not hang in the code,

thank you !

I'm guessing as you said the debugger was enabling the hardware and I was not ???

this gets a little misleading and what is the DWT ???

is this some other timer??,

the code I found on the web for a microsecond timer did not say about enabling any hardware etc.

so the fact my debugger did enable really confused this issue

Thank again 😋

[Tesla DeLorean]

DWT Data Watchpoint & Trace

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0337h/BIIFBHIF.html

It is part of the debug unit that STMicro places on ALL it's parts, it is optional in Cortex-Mx implementations, but it is present here and has very good resolution/granularity. On the F1 parts there were NO 32-bit timers, and at 72 MHz had a wrap time close to a minute.

You don't want to interrupt at 1 MHz, this cycle count is typically good to a few tens of nanoseconds resolution.

You could use a 32-bit TIM, clock that at 1MHz via the prescaler, maximal period (0xFFFFFFFF) and then delta the TIMx->CNT in same manner to count microseconds. No need for it to interrupt, and preferable it doesn't.

The Lock/Access Register is needed on CM7 implementations (ie F7 and H7)

[JHERI]

thank you for the feed back

regards

[Danish1]

I notice that DWT->LAR doesn't seem to exist in core_cm4.h, but does exist in core_cm7.h.

Would I be right in thinking that I don't need to enable it for stm32f4?

Are there significant penalties for enabling DWT? I guess current consumption is tiny compared with the whole core.

[Tesla DeLorean]

I tend to use the top version, the CM7 requires unlocking, sometimes the debugger does this, but in standalone mode you must do it.

It is a 32-bit counter clocking at core frequency, I don't think the impact will be very high in the scheme of things, and it will be of a design that doesn't have critical path issues (carry propagation, etc).

Executing in a tight loop will burn energy, so I would use only for short spin loops where timing is most critical, and for 1ms based ones use SysTick based counts, and WFI to suspend between ticks.