Arduino micros() 方法在 Nano 33 BLE Sense 上执行超过 500 个周期

Question

我先在 Arduino 论坛上发布了这个问题，但我的问题最近没有受到太多关注，所以这里...

我非常努力地制作了一个简单的草图来证明 micros() 方法在 Nano 33 BLE Sense 上有多慢：

#include "mbed.h"
#include "nrf_delay.h"
#include "nrf_gpio.h"

#define OUTPUT_PIN NRF_GPIO_PIN_MAP(1,11)

unsigned long startClock;
unsigned long stopClock;
unsigned long arithmeticMinuend = 4294967295;
unsigned long arithmeticSubtrahend = 2147483648;
unsigned long arithmeticDifference = 0;
unsigned long timeDifference1 = 0;
unsigned long timeDifference2 = 0;

//Assume 1 to 4 clock cycles (15.625 to 62.5 ns) is required for every...
//* call of micros();
//* subtraction of two unsigned longs.
//Therefore we should not be able to measure the time to execute either task by using the micros() - startClock technique, as...
//* micros() - startClock = 0 in either case.

void setup() {
  Serial.begin(115200);
  while (!Serial);

  nrf_gpio_cfg_output(OUTPUT_PIN);

  startClock = micros();
  stopClock = micros();
}

void loop() {
  timeDifference1 = microsecondsToSubtract2LongsOnce();
  timeDifference2 = microsecondsToSubtract2LongsTwice();
  Serial.print("timeDifference1 = ");
  Serial.print(timeDifference1);
  Serial.print(" us.\ntimeDifference2 = ");
  Serial.print(timeDifference2);
  Serial.println(" us.");
  
  microsecondsToSubtract2LongsOnceMeasuredWithScope();
  delay(100);
  microsecondsToSubtract2LongsTwiceMeasuredWithScope();
  delay(100);
  microsecondsToToggleOutputPinMeasuredWithScope();
  
  while(1) {
    
  }
}

//Prints 8 us:
unsigned long microsecondsToSubtract2LongsOnce() {
  startClock = micros();
  stopClock = micros();
  return stopClock - startClock;
}

//Prints 9 us:
unsigned long microsecondsToSubtract2LongsTwice() {
  startClock = micros();
  arithmeticDifference = arithmeticMinuend - arithmeticSubtrahend;
  stopClock = micros();
  return stopClock - startClock;
}

//Measured 18 us on scope:
void microsecondsToSubtract2LongsOnceMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  startClock = micros();
  stopClock = micros();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

//Measured 18 us on scope:
void microsecondsToSubtract2LongsTwiceMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  startClock = micros();
  arithmeticDifference = arithmeticMinuend - arithmeticSubtrahend;
  stopClock = micros();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

//Measured 500 ns on scope:
void microsecondsToToggleOutputPinMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

我将使用示波器进行的时间测量与使用 micros() 进行的时间测量进行比较。通过计算，我们得到一个 micros() 调用所需的时钟周期数 (CC) = (0.5*(18000 - 500) ns)/15.625 ns = 560 CC!! !

谁能举例说明在这个板上测量时间不需要超过 10 CC？？？

根据我的阅读，我认为更快（theoretically 1 CC) strategy would involve using the method nrf_drv_timer or the newer nrfx_timer（这两种策略都需要将定时器设置为在计数器模式下运行），但我找不到在我的 Arduino 的 NRF52840 上使用的具体示例。

编辑：

我也尝试使用 mbed 的 us_ticker 来减少时间，但计时结果完全相同。这是我用于该测试的代码：

#include "mbed.h"
#include "nrf_delay.h"
#include "nrf_gpio.h"

#define OUTPUT_PIN NRF_GPIO_PIN_MAP(1,11)

mbed::Timer timer;

uint32_t startClock;
uint32_t stopClock;
uint32_t arithmeticMinuend = 4294967295;
uint32_t arithmeticSubtrahend = 2147483648;
uint32_t arithmeticDifference = 0;
uint32_t timeDifference1 = 0;
uint32_t timeDifference2 = 0;

//Assume 1 to 4 clock cycles (15.625 to 62.5 ns) is required for every...
//* call of micros();
//* subtraction of two unsigned longs.
//Therefore we should not be able to measure the time to execute either task by using the micros() - startClock technique, as...
//* micros() - startClock = 0 in either case.

void setup() {
  Serial.begin(115200);
  while (!Serial);

  nrf_gpio_cfg_output(OUTPUT_PIN);
  timer.start();
  startClock = timer.read_us();
  stopClock = timer.read_us();
}

void loop() {
  timeDifference1 = microsecondsToSubtract2LongsOnce();
  timeDifference2 = microsecondsToSubtract2LongsTwice();
  Serial.print("timeDifference1 = ");
  Serial.print(timeDifference1);
  Serial.print(" us.\ntimeDifference2 = ");
  Serial.print(timeDifference2);
  Serial.println(" us.");
  
  microsecondsToSubtract2LongsOnceMeasuredWithScope();
  timer.stop();
  delay(100);
  timer.start();
  microsecondsToSubtract2LongsTwiceMeasuredWithScope();
  timer.stop();
  delay(100);
  timer.start();
  microsecondsToToggleOutputPinMeasuredWithScope();
  timer.stop();
  
  while(1) {
    
  }
}

//Prints 8 us:
unsigned long microsecondsToSubtract2LongsOnce() {
  startClock = timer.read_us();
  stopClock = timer.read_us();
  return stopClock - startClock;
}

//Prints 9 us:
unsigned long microsecondsToSubtract2LongsTwice() {
  startClock = timer.read_us();
  arithmeticDifference = arithmeticMinuend - arithmeticSubtrahend;
  stopClock = timer.read_us();
  return stopClock - startClock;
}

//Measured 18 us on scope:
void microsecondsToSubtract2LongsOnceMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  startClock = timer.read_us();
  stopClock = timer.read_us();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

//Measured 18 us on scope:
void microsecondsToSubtract2LongsTwiceMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  startClock = timer.read_us();
  arithmeticDifference = arithmeticMinuend - arithmeticSubtrahend;
  stopClock = timer.read_us();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

//Measured 500 ns on scope:
void microsecondsToToggleOutputPinMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

Answer 1

这是一个使用 mBed 的 us_ticker_read 的策略，它比 Arduino 的 micros 或 mBed 的 read_us 快一个数量级以上，即 650 ns或 42 CC.

#include "mbed.h"
#include "nrf_delay.h"
#include "nrf_gpio.h"

#define OUTPUT_PIN NRF_GPIO_PIN_MAP(1,11)

uint32_t startClock;
uint32_t stopClock;
uint32_t arithmeticMinuend = 4294967295;
uint32_t arithmeticSubtrahend = 2147483648;
uint32_t arithmeticDifference = 0;
uint32_t timeDifference1 = 0;
uint32_t timeDifference2 = 0;

//Assume 1 to 4 clock cycles (15.625 to 62.5 ns) is required for every...
//* call of micros();
//* subtraction of two unsigned longs.
//Therefore we should not be able to measure the time to execute either task by using the micros() - startClock technique, as...
//* micros() - startClock = 0 in either case.

void setup() {
  Serial.begin(115200);
  while (!Serial);

  nrf_gpio_cfg_output(OUTPUT_PIN);
  us_ticker_init();
  startClock = us_ticker_read();
  stopClock = us_ticker_read();
}

void loop() {
  Serial.println("Starting program:");
  timeDifference1 = microsecondsToSubtract2LongsOnce();
  timeDifference2 = microsecondsToSubtract2LongsTwice();
  us_ticker_free();
  Serial.print("timeDifference1 = ");
  Serial.print(timeDifference1);
  Serial.print(" us.\ntimeDifference2 = ");
  Serial.print(timeDifference2);
  Serial.println(" us.");

  us_ticker_init();
  microsecondsToSubtract2LongsOnceMeasuredWithScope();
  us_ticker_free();
  delay(10);
  us_ticker_init();
  microsecondsToSubtract2LongsTwiceMeasuredWithScope();
  us_ticker_free();
  delay(10);
  us_ticker_init();
  microsecondsToToggleOutputPinMeasuredWithScope();
  us_ticker_free();
  
  while(1) {
    
  }
}

//Prints 1 us:
uint32_t microsecondsToSubtract2LongsOnce() {
  startClock = us_ticker_read();
  stopClock = us_ticker_read();
  return stopClock - startClock;
}

//Prints 1 us:
uint32_t microsecondsToSubtract2LongsTwice() {
  startClock = us_ticker_read();
  arithmeticDifference = arithmeticMinuend - arithmeticSubtrahend;
  stopClock = us_ticker_read();
  return stopClock - startClock;
}

//Measured 1.8 us on scope:
void microsecondsToSubtract2LongsOnceMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  startClock = us_ticker_read();
  stopClock = us_ticker_read();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

//Measured 2 us on scope:
void microsecondsToSubtract2LongsTwiceMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  startClock = us_ticker_read();
  arithmeticDifference = arithmeticMinuend - arithmeticSubtrahend;
  stopClock = us_ticker_read();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

//Measured 500 ns on scope:
void microsecondsToToggleOutputPinMeasuredWithScope() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

如果谁能在接下来的几天里post一个时间更快的例子，我会采纳他们的回答！

编辑（11/12/2021）：

我应该感谢 Arduino 论坛上的 westfw 引导我朝着正确的方向前进。他建议的策略非常准确，只需 1 或 2 CC 即可执行：

#include "mbed.h"
#include "nrf.h"
#include "nrf_delay.h"
#include "nrf_gpio.h"

#define OUTPUT_PIN NRF_GPIO_PIN_MAP(1,11)

const float MICROS_PER_CYCLE = 0.015625; //Nano 33 BLE Sense operates at 64 MHz -> 15.625 ns/cc.
const byte BYTE_TO_SEND = 170; //b'10101010'.
const int BYTES_PER_TRANSFER = 54;

byte buffer[BYTES_PER_TRANSFER];

volatile uint32_t stopWatchTime1;
volatile uint32_t stopWatchTime2;
volatile uint32_t stopWatchTime3;

void setup(){
  Serial.begin(1000000); //Does nothing on the Nano 33 BLE Sense.
  while (!Serial); //Wait for serial port to connect. Needed for native USB CDC on Nano 33 BLE Sense.

  stopWatchInit();
  
  nrf_gpio_cfg_output(OUTPUT_PIN); //Configure pin as digital output for measuring time of events on scope.
  
  memset(buffer, BYTE_TO_SEND, sizeof(buffer));

  //Measured 300 ns on scope and printed 190 ns.
  togglePinTwice();
  delay(10);

  //Measured 840 ns on scope and printed 730 ns:
  togglePinTwiceAndCallMicrosTwice();
  delay(10);

  //Measured ~68 us on scope and printed 67.69 us:
  togglePinTwiceCallMicrosTwiceAndWriteBytes(); //This result makes sense bc 88 - 9.2 = 78.8 us (which is basically 78 us).
  delay(10);

  //Measured ~68 us on scope:
  togglePinTwiceAndWriteBytes();

  Serial.println("");
  Serial.print(MICROS_PER_CYCLE*((float)stopWatchTime1));
  Serial.println(" us");
  Serial.println("");
  Serial.print(MICROS_PER_CYCLE*((float)stopWatchTime2));
  Serial.println(" us");
  Serial.println("");
  Serial.print(MICROS_PER_CYCLE*((float)stopWatchTime3));
  Serial.println(" us");
}
  
void loop(){}

void togglePinTwice(){
  stopWatchStart();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  stopWatchTime1 = stopWatchGet();
}

void togglePinTwiceAndCallMicrosTwice() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  stopWatchStart();
  stopWatchTime2 = stopWatchGet();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

void togglePinTwiceCallMicrosTwiceAndWriteBytes() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  stopWatchStart();
  Serial.write(buffer, sizeof(buffer));
  Serial.flush(); //Patch current Serial.h to use or it will block forever.
  stopWatchTime3 = stopWatchGet();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

void togglePinTwiceAndWriteBytes() {
  nrf_gpio_pin_toggle(OUTPUT_PIN);
  Serial.write(buffer, sizeof(buffer));
  Serial.flush();
  nrf_gpio_pin_toggle(OUTPUT_PIN);
}

void stopWatchInit() {
  CoreDebug->DEMCR |= 0x01000000; //Enable the use of DWT.
}

void stopWatchStart() {
  DWT->CYCCNT = 0; //Reset cycle counter.
  DWT->CTRL |= 0x1; //Enable cycle counter.
}

uint32_t stopWatchGet() {
  return DWT->CYCCNT; //Number of clock cycles stored in count variable.
}

Answer 2

我的“提示”，供参考：

对于短时间间隔，您应该能够从 ARM Core SysTick 定时器或 ARM DWT 循环计数器读取循环计数（您可能必须先启用 DWT。）

    startTime = SysTick->VAL; // 24bit counter, probably resets at ~1ms.  Counts Down!
// or
    start = DWT->CYCCNT;  //CYCCNT wraps at 32bits; never resets, counts up.
// With:
  // Somewhere in system init
  CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
  DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;

我不知道这些将如何受到（或影响）低功耗模式等的影响。（特别是DWT可能会耗电，不知道在powerdown模式下会不会关机。）

Arduino micros() 方法在 Nano 33 BLE Sense 上执行超过 500 个周期

Arduino's micros() method is taking over 500 cycles to execute on Nano 33 BLE Sense

timer

arduino

timing

nrf52

arduino-nano