Almost Cycle-accurate measurements

[cnlohr]

• You can use SYSCLK to get a 32-bit timer count for cycles from the system clock, so you don't have to worry about overflows
• You can use the AWU IRQ Handler to get interrupts when the AWU triggers.

This lets you capture the data very quickly, and with much more precision than currently available.

#include "ch32v003fun.h"
#include <stdio.h>

#define ITERATIONS 1
#define SERIALPLOT

volatile uint32_t ldelta;
uint32_t llast;

void AWU_IRQHandler( void ) __attribute__((section(".text.vector_handler")))  __attribute__((interrupt));

void AWU_IRQHandler( void )
{
	uint32_t l = SysTick->CNT;
	ldelta = (l - llast);
	llast = l;
	EXTI->INTFR = EXTI_Line9;
}

int main()
{
	SystemInit();

	// enable power interface module clock
	RCC->APB1PCENR |= RCC_APB1Periph_PWR | RCC_APB1Periph_WWDG;

	// enable low speed oscillator (LSI)
	RCC->RSTSCKR |= RCC_LSION;
	while ((RCC->RSTSCKR & RCC_LSIRDY) == 0) {}

	// enable AutoWakeUp event
	EXTI->FTENR |= EXTI_Line9;
	EXTI->INTENR |= EXTI_Line9;

	// configure AWU prescaler and configure AWU window comparison value
	// /16 /(63+1) ~= 120Hz
	PWR->AWUPSC = PWR_AWU_Prescaler_8;
	PWR->AWUWR = 63;
	PWR->AWUCSR = (1 << 1); // AWUEN

	// enable interrupt
	NVIC_EnableIRQ( AWU_IRQn );

	uint32_t t;
	uint32_t lastt = TIM1->CNT;

	while(1)
	{
		// Wait for data to become available.	
		uint32_t printtime = 0;
		while( !( printtime = ldelta ) );
		ldelta = 0;
		printf("%d\n", printtime ); //raw_to_temperature(count));
	}
}

Just tested it at my desk here.

Also, I am seeing significant variation per part.

Part Test	Count at 25C	Count at -19 C	Counts Per Deg C
1	200300	203100	63
2	211000	215000	90
3	189500	192100	59

Additionally flex your PCB

Quescent at 25 C: 189900
Diagonal Torsion: 1888537
Inverse Torsion: 191050

Just using my little PCBs I had at my desk applying about 1 N*cm of force to the PCB.

[eeucalyptus]

I'll look into it tonight, thank you for the input!