CH32V003 und Arduino           

#include <HardwareTimer.h>
HardwareTimer myTimer(TIM2);

int myPort= PD4, myLED, time_span, i;

void timerHandler(void)
{ myTimer.pause();
  digitalWrite(myPort,HIGH);
  delayMicroseconds(time_span);
  myTimer.setOverflow(5000-time_span, MICROSEC_FORMAT);
  myTimer.resume();
  digitalWrite(myPort, LOW);
}
void setup() {
  Serial.begin(115200);
  pinMode(myPort, OUTPUT);
  myLED= LOW;
  myTimer.attachInterrupt(timerHandler);
  myTimer.resume();
}
void loop()
{ for(i=500;i<2500;i++) { time_span = i; delay(1); Serial.println(i);}
  for(i=2500;i>500;i--) { time_span = i; delay(1); Serial.println(i);}
}

.equ R32_GPIOC_CFGLR,   0x40011000
.equ R32_GPIOC_BSHR,    0x40011010
.equ R32_RCC_APB2PCENR, 0x40021018

.global setup
.global loop

setup:
  li   t0,R32_RCC_APB2PCENR     // load address of APB2PCENR register to t0 ,for enabling GPIO A,D,C peripherals
  lw   t1,0(t0)                 // load contents from peripheral register R32_RCC_APB2PCENR pointed by t0
  li   a1,(1<<4)                // 1<<<<IOPC_EN
  or   t1,t1,a1                 // or values 
  sw   t1,0(t0)                 // store modified enable values in R32_RCC_APB2PCENR

  li   t0,R32_GPIOC_CFGLR       // load pointer t0 with address of R32_GPIOC_CFGLR , GPIO configuration register
  li   t1,0x00030000            // set PORTC register for pin4 as push-pull output (PC4)
  sw   t1,0(t0)                 // store in R32_GPIOC_CFGLR

  li   t1,(1<<4)                // value for setting  pin4 (PC4)
  li   t2,(1<<(16+4))           // value for clearing pin4 (PC4)

  li   t0,R32_GPIOC_BSHR        // R32_GPIOC_BSHR register sets and resets GPIOC pins, load address into pointer t0

loop:
PC4_ON:
  sw   t1,0(t0)                 // store t1 to R32_GPIOC_BSHR
  call _delay                   // delay subroutine
PC4_OFF:
  sw   t2,0(t0)                 // store t2 to R32_GPIOC_BSHR
  call _delay                   // delay subroutine
  j loop                        // repeat

_delay:                         // delay routine
  li   a1,3000000               // load an arbitarary value 3000000 to t1 register for 1sec blink at 24MHz clock cycle
delay_loop:
  addi a1,a1,-1                 // subtract 1 from t1
  bne  a1,zero,delay_loop       // if t1 not equal to 0 branch to label loop
  ret                           // return to caller