For microseconds based delay, DWT cycle counter is used to get maximal optimized delay. Regards, Ritesh Prajapati. The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency (in Hertz). Go to left sidebar of the IDE, click the “ New file ” button and it will create a new file and it will open with in editor window as a untitled name. on May 31, 2018. Each group has two general-purpose hardware timers. ESP32-DevKi…. I use an ADPS-9960 for gesture control which triggers an external interrupt. 010ms from the moment the trigger is received until the output is. I also used portTICK_RATE_MS but the speed didnt change . ”を10回表示の比較になります。 1000us毎は早すぎて一瞬ですので違いがわかります。The bug affected ESP32-S3 only. Hopefully i have not overlooked. Espressif ESP32 Official Forum. mktime(t: struct_time) → int. 0. These ESP32 Hardware Timers, using Interrupt, still work even if other functions are blocking. ago. ESP32 uses two hardware timers for the purpose of keeping system time. So for a hundred microsecond delay do: for(int loop = 0; loop < 3; loop++) {int samp = adc1_get_raw((adc1_channel_t)channel2); } It goes without saying that this a workaround for a systematic solution; This delay is jittery, as the higher priority processes will interfere. Moreover, they are much more precise (certainly depending on clock frequency. But make sure to do the time unit conversion and pass to it the desired time in milliseconds. If you need better resolution, micros () may be the way to go. We have 10 and 40 microseconds delay requirement for our application development purpose. This is the code #include <ESP32Servo. I don't know what the valid maximum value to call with is,. So, Normal communication with that module using ESP32 is UART but. e delay(6400) equal… Hi guys. INCLUDE_vTaskDelayUntil must be defined as 1 for this function to be available. I also used portTICK_RATE_MS but the speed didnt change . Step 3: Open the Example File in Your Arduino IDE. commit () after the above steps. ’. 2, a 32-bit hardware timer was used. Plenz September 19, 2015, 9:45am 1. I dont get any delay even if I add some different delays. This function can help install the low level putc function for esp_rom. Re: vTaskDelay () vS. -. deepsleep ([time_ms]) ¶ Stops execution in an attempt to enter a low power state. Could you give a example of code in (RTOS) C for ESP32 using the right lib? I saw the blinky example, but it's based on milliseconds, and on callback functions for os_timer functions. I call vTaskDelay for various reasons. Posted by rtel on December 24, 2014. Let me know if anyone has any idea for that. (builtinLED, LOW); delay(100); }} The ESP32 RTC wakes the ESP32 microcontroller from sleep mode after a period of time has elapsed, with the instruction esp_sleep_enable_timer_wakeup(N), where N is the required number of microseconds. So in that module, we need exact delay of 10 and 40 microseconds of delay interval in some interval to update firmware into that module using one wire communication over GPIO pins. These values are in microseconds when the timer reach a_value do something. Among the functions available to it, the following can be highlighted: Scheduled execution every x milliseconds and even microseconds. On the small end of the scale are the steppers used within DVD. The maximal possible delay is 768 us / F_CPU in MHz. Step-By-Step Instructions To Connect The TB6600 Module with ESP32. There is a delay I've created in the smoothing loop using millis() which I believe is working correctly. Seeing this, I bought the ESP32 knowing that it had a much faster CPU clock speed and overall performance compared against the Nano. I am trying to do accurate timing using the ESP32 64 bit counter which use the 80 MHz APB clock. I am trying the run stepper motor with the tmc2208 driver and ı want to delay in microseconds like 5uS or 10 uS. (Actually to be correct I believe one should have be added to the # milliseconds in this calculation). sleep_ms() ). The 975 microseconds can be. Should we use "delay()" as we don't want the 25 microseconds to be interrupted. Currently, the largest value that will produce an accurate delay is 16383; larger values can produce an extremely short delay. Há mil microssegundos em um milissegundo, e um milhão de microssegundos em um segundo. At the moment ESP32 plugged to serial monitor about 23hours ticking, the millis() was working fine. This is all very helpful stuff for your projects. The interrupt is triggered with the rising and falling edge and store the start & endtime with the funktion micros() in two diffrent variables. 5us delay when ESP works at 80MHz. I checked flash frequency is 40MHz (80 seems to lead to same issues) Anyway, if I start the device at 10:00:34, it will restart at 10:01:00. Subtracting 53 from every count gives me a count accurate to within a few tens of picoseconds, for periods from 30 microseconds to about 500 microseconds. You say "2 and 8 µS, or even more, is OK. If you use external libraries in your code. Step 4: Connect the potentiometer to the ESP32. And for this reason, the prescaler value is 72. 2 also, with 96 MHz clock. Web Remote Controlled Servo. The exact hardware timer implementation used will depend on the target, where LAC timer is used for ESP32. So I assume you are using arduino-esp32 as a component with your own sdkconfig settings? Correct, the default esp-idf settings. Free book on ESP32 available here:. A única opção não recomendada é um loop baseado na função millis (). 1 or // 2 microseconds) gives delays longer than desired. ESP32 crashes when I call the function after ~1 hour 20 minutes of usage, becaus. 1. On the boards from the Arduino Portenta family this function has a resolution of one microsecond on all cores. Top 1 post • Page 1 of 1We have 10 and 40 microseconds delay requirement for our application development purpose. Especially that I need to wire it without a. Problem is, I cannot start them from outside before the time is over. However, this crashes my ESP32 every time. dmaxben Posts: 108 Joined: Thu Nov 16, 2017 6:04 pm. Sets how quickly the timer counter is “ticking”. Pauses the program for the amount of time (in microseconds) specified by the parameter. The ESP32 uses the function name "setTimeOut" (as in the Stream class) and uses that for low level I2C code. I am trying the run stepper motor with the tmc2208 driver and ı want to delay in microseconds like 5uS or 10 uS. I also used portTICK_RATE_MS but the speed didnt change . After some playing and toying I decided to try esp-idf to. Then I found out time delay function delays 6. I need accuracies of 1 ppm or better. Dimming Neopixels, Delays<Microseconds. rulers. 5 ms for neutral position. 96” OLED. This code is written in Keil uvision. When an interrupt occurs it causes the processor to stop, save its state, do a new task, then restore its state and continue. Top. I've tried with esp-idf coding and Arduino coding. Duemilanove and Nano. cc analogRead() - Arduino Reference. So in that module, we need exact delay of 10 and 40 microseconds of delay interval in some interval to update firmware into that module using one wire communication over GPIO pins. In esp32_hal::delay? Struct esp32_hal:: delay:: Delay source · [−] pub struct Delay { /* private fields */ } Expand description. esp_timer set of APIs provides one-shot and periodic timers, microsecond time resolution, and 64-bit range. With a normal LEDs you can show the state of a system (blue= too cold, red= too hot). arduino. Delay driver. I am trying the run stepper motor with the tmc2208 driver and ı want to delay in microseconds like 5uS or 10 uS. One of the best things about Arduino is the ability to just block for a period with: delay (1000); // hang on a second, buddy. The ESP32 SoCs contains from 2 to 4 hardware timers. Problem acquiring data on esp32 for geiger counter. begin()は、Bluetoothシリアルに名前を指定します。指定した名前でペアリングします。 SerialBT. Finally I created the code below that does not display a zero but the text "resetting the sensor" and then pushes the signal of the echo into LOW. Using "delayMicroseconds ()", that delay can be specified with microsecond resolution. ESP32 crashes when I call the function after ~1 hour 20 minutes of usage, becaus. We have 10 and 40 microseconds delay requirement for our application development purpose. If 0 is passed as the argument, the delay will equal the time spent executing the interrupt service routine. Let me know if anyone has any idea for that. Initializing Timer Interrupt in Raspberry Pi Pico. Code that executes faster can also have other positive effects, e. especially if nested interrupts is all working as it should…’ that’s how I fire the firing pin at exactly the time it. or maybe increase the bit resolution. With a normal LEDs you can. This timer is handled automatically by the underlying code in the Arduino Core. rikoubou. After getting the code to work on the ESP32 with a few changes, I ran a speed test again, and got the same 80ms. Using "nop" command gives me 0. Read part 1. time. Description. When ı create a task using xTaskCreate() function and adding some delay in the task function. 1. shown in. I dont get any delay even if I add some different delays. Register; Logout; Contact us; Board index English Forum. ESP32 supports two major power saving modes: Light-sleep and Deep-sleep. A única opção não recomendada é um loop baseado na função millis (). The value should be treated as opaque, suitable for use only with ticks_diff(). The second ISR would be connected to the Timer. You may replace all delay with this function. As shown on the oscilloscope screenshot below, why is the interrupt triggered twice ? The issue is the same if I use different GPIO pins for the interrupt and gate. . 3. A remote program on a PC connects to this server and then the ESP32 sends a 100byte message 100. Bakedintheusa • 5 mo. delay() Specifies program pauses a number of milliseconds. There are 7 kinds of micro steps (1, 2 / A, 2. Certain things do go on while the delay () function is controlling the Atmega chip, however, because the delay function does not disable interrupts. Top. one micro second at a time. If anyone was wondering, the answer is a lot easier than what I thought. ESP8266EX and ESP32 are. Code that executes faster can also have other positive effects, e. attachInterrupt (digitalPinToInterrupt (pin), ISR, mode) GPIOPin – sets the GPIO pin as an interrupt pin, which tells the ESP32 which pin to monitor. delayMicroseconds() works in arduino. 3 microseconds on a 240 MHz ESP32 ~0. First, we will learn to interface HC-SR04 with ESP32. ) to perform the delay. Low uS delays will not be easy in software because another task/ISR might cut across you. 1 milliseconds) to read. In the Extension, select ESP-IDF option: We will click the ‘ esp_timer ’ under the System tab. This timer would print “timer callback” every 1000 milliseconds. Struct esp_idf_hal :: delay :: Ets. I’d love some help here. hatenablog. Now click ‘ Create project using template esp_timer . When ı create a task using xTaskCreate() function and adding some delay in the task function. 3V. 2 (depending on compiler settings) uses the computed goto feature of the GCC compiler. I edited the example code and removed all I. Introducing the HC-SR04 Ultrasonic Sensor. First of all, the timer should be initialized by calling the function timer_init () and passing a structure timer_config_t to it to define how the timer should operate. So in most cases, it will loop once, in the worst case it will loop twice. red. When ı create a task using xTaskCreate() function and adding some delay in the task function. Top. Currently, the largest value that will produce an accurate delay is 16383. Delay a task until a specified time. In addition, this particular module comes with ultrasonic transmitter and receiver. Pausa o programa pela quantidade de tempo especificada como parâmetro (em microssegundos). 1. analogWrite (4, 5, 1000, 10, 0); analogWrite (5, 5, 1000, 10, 4); analogWrite (12, 5, 1000, 10, 8); EDIT 1: If getting all 3 signals to synchronize properly is an issue, then using the ESP32's MCPWM hardware might be an option. h>. When ı create a task using xTaskCreate() function and adding some delay in the task function. That is how other arduino boards work and a lot of code and libraries expect delay to work as per the. Since we use the GPIOs on ESP32, you can complete the connections with fewer wires. The FRC2 is a legacy option for ESP32 until v4. Parameters. Hello community, I made a function that should be able to create a delay for a certain number of microseconds, here the code. The wiring is done as shown with 2 exceptions. Arduino example sketch "Blink" allows you to specify "delay ()" between state. I chose the ESP32 because of its 240MHz clock, but it still seems to be having trouble. So the ESP32 starts booting but does not go in normal operating mode. Optimizing execution speed is a key element of software performance. vTaskDelay(500 / portTICK_RATE_MS); You can use vTaskDelay () even if not using FreeRTOS tasks. I also used portTICK_RATE_MS but the speed didnt change . ino" file with it, as a second tab. The function timerBegin (uint8_t id, uint16_t prescaler, bool countUp) allows to configure the timer : The ESP32 has 4 independent timers, selected by an id between 0 and 3. ESP32 is a series of low cost, low power system on a chip microcontrollers with integrated Wi-Fi and dual-mode Bluetooth. Consult the ESP32 datasheet for details on pin internal pull-ups. I dont get any delay even if I add some different delays. The esp32 has WiFi and ESP-NOW active at the same time, receiving some data from another esp32. The VCC and GND pins of the Waterproof ultrasonic sensor are connected to the ESP32 3. You can upload the code provided to your ESP32 by connecting two buttons to GPIO 2 and GPIO 15. This number represents the time and is measured in microseconds. Using techniques like microstepping the position of the motor shaft can be controlled with a great deal of precision. ESP32 Timer Example (Arduino) Let’s say we’d like to toggle an LED every 1 ms without using a delay that blocks the CPU and does much harm to the overall timing performance of your system. I can not understand what this delay depends on. Use a N-Channel MOSFET. Arm/Start the timer , in case you detached the interrupt attach it back. They are all 64-bit generic timers based on 16-bit pre-scalers and 64-bit. This function is used to configure the timer. The available modules are generally composed of an ultrasonic transmitter, a receiver, and a chip that controls them. I’ve updated my delay library to support milliseconds and microseconds delays. I did need a multiple MHz blink, and thus a nanosecond delay. I am trying the run stepper motor with the tmc2208 driver and ı want to delay in microseconds like 5uS or 10 uS. I am using the ESP32 servo library to control an ESC for a brushless motor. We’ve. Its argument is the struct_time or full 9-tuple (since the dst flag is needed; use -1 as the dst flag if it is unknown) which expresses the time in local time, not UTC. sleep_us(us): This is yet another blocking method that provides a delay in microseconds. You can set its micro step and output current with 6 DIP switch. I'm messing around with the following code: #define cyclespermicro 240 #define microcycles (n) (n*cyclespermicro) uint32_t startCounter, counter, cpu_cycles; int. esp_err_t esp_timer_start_periodic (esp_timer_handle_t timer, uint64_t period) ¶ Start a periodic timer. I have begun to interest in how FreeRTOS works, and because of I don't have my ESP32 yet, i decided to try it in my arduino micro. So your clock processor clock should be > 1 MHZ (which it is. 3. ticks_ms ¶ Returns an increasing millisecond counter with arbitrary reference point, that wraps after some (unspecified) value. Instead use delayMicroseconds(); for instance delayMicroseconds(500); for 500us and delayMicroseconds(1250); for 1. I first tried the standard C/C++ sleep() method, but if I. Arduino micros () Function. With the Nano, it took roughly 80000 microseconds exactly with little deviation. There are a thousand microseconds in a millisecond and a million microseconds in a second. I did need a multiple MHz blink, and thus a nanosecond delay between state changes. What's the reason or how can I get shorter delay when the smallest delay which I can use using assembler "nop" command gives me 0. void esp_rom_install_channel_putc (int channel, void (* putc) (char c)) esp_rom_printf can print message to different channels simultaneously. I’ll try and attach a screen shot here: Here is the code for the program. Top. ESP_OK on. The actual time that the task remains blocked depends on the tick rate. The main idea is to start a timer for a given amount of time (say 5 seconds) whenever an external button is pushed. vTaskDelay issue bit me. Return. h>. h) will allow you to busy-wait for a correct number of microseconds. This function will return timer structure if configuration is successful. I dont get any delay even if I add some different delays. 2. Therefor I set an interrupt on the according pin. ESP32 to be powered by smallest sized solar panel possible, or possibly battery. This means that we can control the stepper motor with just 2 pins from our controller, or one for controlling the rotation direction and the other for controlling the steps. I want to read analog signal via adc with sample rate about 48khz so when I read via adc and delay about 20us. On the boards from the Arduino Portenta family this function has a resolution of one microsecond on all cores. After that, we will see example codes with or without the Ultrasonic sensor Arduino library. I sadly dont have an ESP32 with me at the moment, so I cant check it myself. To open the project in a new window, click ‘Yes. Here is what you need to do to install the ESP32 boards into the Arduino IDE: Open the Arduino IDE. This could change in future Arduino releases. Returns the number of microseconds since the Arduino board began running the current program. Introduction. The calculation of the duration take place later. Top. The stepper driver supports speed and direction control. ⚡ESP32 Code Example For The Servo Motor Project. Let's say portTICK_PERIOD_MS = 10 and you call delay(9). Currently, the largest value that will produce an accurate delay is 16383. Looking further, lwip's sntp and settimeofday() should already be using the microseconds portion of ntp timestamps. I don't have the proper hardware for that. ESP32 crashes when I call the function after ~1 hour 20 minutes of usage, because esp_timer_get_time() return a int64_t value and is parsed as uint32_t in delayMicroseconds(). 25); . cpp 📋 Copy to clipboard ⇓ Download. Top 1 post • Page 1 of 1Power Supply Requirements of TB6600. With a normal LEDs you can. With a normal LEDs you can show the state of a system (blue= too cold, red= too hot). Delays<Microseconds. Otherwise the sleep can last indefinitely. This number will overflow (go back to zero), after approximately 70 minutes. Milliseconds based delay is done using systick timer which makes interrupts every 1ms generated by HAL library. g. Wiring the GPIO0 to VCC and GPIO12 to GND helps but is not so very nice. I dont get any delay even if I add some different delays. I am trying the run stepper motor with the tmc2208 driver and ı want to delay in microseconds like 5uS or 10 uS. analogWrite (4, 5, 1000, 10, 0); analogWrite (5, 5, 1000, 10, 4); analogWrite (12, 5, 1000, 10, 8); EDIT 1: If getting all 3 signals to synchronize properly is an issue, then using the ESP32's MCPWM hardware might be an option. kolban Posts: 1683 Joined: Mon Nov 16, 2015 4:43 pm Location: Texas, USA. II. pyb. I also used portTICK_RATE_MS but the speed didnt change . Do it correctly. On the ESP32, this is the APB_CLK clock, clocked at 80 MHz. So is there a way I can implement a delay… Espressif ESP32 Official Forum. vTaskDelay(500 / portTICK_RATE_MS); You can use vTaskDelay () even if not using FreeRTOS tasks. However, I just found. microsteps set to 8X* (M2 to ground). 最終目標は、Bluetoothを用いて電光掲示板の表示内容を切り替えるプログラム作成できるようになることです。. The time loss always varies but for a general concept 5-10 minutes over 1 hour are lost. So in that module, we need exact delay of 10 and 40 microseconds of delay interval in some interval to update firmware into that module using one wire communication over GPIO pins. 8inch to 157inch) with an accuracy of 0. This function returns the number of microseconds since esp_timer was. machine. Internally, esp_timer uses a 64-bit hardware timer. Overview. Optimizing execution speed is a key element of software performance. )Step-By-Step Instructions To Connect The A4988 Driver Module with ESP32. I am trying the run stepper motor with the tmc2208 driver and ı want to delay in microseconds like 5uS or 10 uS. timeout_us: timer timeout, in microseconds relative to the current moment . In the sketch above, the argument of the initialize() function is 5000000 microseconds, so the timer interrupt will be triggered once every five seconds. 8 second stalls when TCP running, less than 10k/sec throughput. hw_timer_t * timerBegin(uint32_t frequency); frequency select timer frequency in Hz. I also used portTICK_RATE_MS but the speed didnt change . It can't be that slow because there is absolutely nothing else that takes time except potentially this one. Let me know if anyone has any idea for that. For delays longer than a few thousand microseconds, you should use delay () instead. Perform a delay of __us microseconds, using _delay_loop_1(). I read the first block but never the second. The resolution for micros() is 4 microseconds on all 16MHz Arduino boards: Uno, Mega, Nano, etc. I dont get any delay even if I add some different delays. Example run (the last value is delay in usec, which should be 14, but it's more): I (4895) main: 7:2304(28) I (7472) main:. This guide also includes a comparison of vTaskDelay () function provided by FreeRTOS with. This guide also includes a comparison of vTaskDelay () function provided by FreeRTOS with different delay values in milliseconds. It does some delay + gpio, and measures the timing using ccount. Posts: 36 Joined: Sat Mar 23, 2019 8:39 am. //gpio to use to trigger delay const. 3V making it 4. The Wi-Fi driver can be considered a black box that knows nothing about high-layer code, such as the TCP/IP stack, application task, and event task. If issue persists, open issue in related Ethernet library or ESP32/ESP8266. Use Linux or MacOS. When the timer expired it would be triggered. Step 2: Connect the PWM line. If it is used for a timer interrupt, the delay can extend till the execution of the interrupt service routine is finished. Now, this seems a pretty much straight forward and easy task and everything works fine until the esp32 is powered using an external power supply say mobile charger of 5v2amp. Let me know if anyone has any idea for that. These ESP32, ESP32_S2, ESP32_S3 or ESP32_C3 Hardware Timers, using Interrupt, still work even if other functions are blocking. vTaskDelayUntil is absolute in terms of the ticks set by scheduler and FreeRTOS Kernel. ). However, improving execution speed may have trade-offs with other aspects of performance such as Minimizing Binary Size. ”を10回表示、1000us毎に”. It is microseconds and not milliseconds. System time can be kept by using either one or both of the hardware timers depending on the application’s purpose and accuracy requirements for. Espressif ESP32 Official Forum. The motor interface type must be set to 1 when using a step and direction driver. delay(60000); // 1 minute = 60x1000 = 60,000 milliseconds. COROUTINE_DELAY_SECONDS(seconds): yields back execution for seconds. Hi everyone! I want to implement a timing delay of 1us in my program. So not just an ESP32 issue. DFRobot Beetle ESP32-C3 Datanoise PicoADK Deneyap Kart Deneyap Kart 1A Deneyap Kart 1A v2 Deneyap Kart G Deneyap Mini Deneyap Mini v2 DynOSSAT-EDU-EPS DynOSSAT-EDU-OBC E-Fidget ELECFREAKS PICO:ED ES3ink ESP 12k NodeMCU ESP32 Devkit V1 ESP32-C3-DevKitM-1 ESP32-C6-DevKitC-1-N8 ESP32-C6-DevKitM-1. Delay a task for a given number of ticks. Hi all, I'm a new member. It does not interact with RTOS and calling it will actually block everything for 100ms, if it is called from higest-priority task. h. Interrupts on ESP32 are soft IRQ's and are subject to latency which can run to milliseconds, especially on SPIRAM boards, On a Pyboard latency is on the order of 15μs. Serial communication that appears. The first time, the value is wrong of course, but after that, it is the microseconds outside the loop() function. This function is used to configure the timer. profile ): $ export MDK=/path/to/mdk # Points to MDK directory $ export ARCH=esp32c3 # Valid choices: esp32 esp32c3 $ export PORT=/dev/ttyUSB0 # Serial port for flashing. Step 1: Start with the GND connections. There are a thousand microseconds in a millisecond, and a million microseconds in a second. Most of the time, the measurement shows 14us (1170 cpu cycles at 80mhz). Pauses the program for the amount of time (in microseconds) specified by the parameter. I’m trying to figure out how to do the same thing from within a lambda. Secondly, the custom event handler which you've given your HTTP client ( _gets called for each relevant event in the HTTP download, so use that to see how long each step takes. It’s also one of the worst things. I dont get any delay even if I add some different delays. 1inches), which is good for most hobbyist projects. And the most important things that delay() will pause the execution of other codes. Free book on ESP32 available here:. But for some reason Timer0 is being disabled, and can't use the delay(), millis() and delayMicroseconds(). I am trying the run stepper motor with the tmc2208 driver and ı want to delay in microseconds like 5uS or 10 uS. hw_timer_t * timerBegin(uint32_t frequency); frequency select timer frequency in Hz. Background: With some switching power supplies the rise up time of the power is too long. For ESP32’s power-up and reset sequence timing diagram, please refer to Section Power Scheme in ESP32 Datasheet. //gpio to use to trigger delay const. So, my RealTime Worry is: ESP32 co-hosting Wifi, Server, engine/generator controller state machine, with needed delays and timeout checks. 3cm (0. First, we will learn to interface HC-SR04 with ESP32. 3V ESP32 was not going high enough to turn off the Opto-isolators. Note that this is busy-waiting, so unlike vTaskDelay it does not allow other tasks to run (it just burns CPU cycles. FAQ; Forum. Tested and working Pinout. The delay function pauses the execution of your sketch for the duration of the delay. rikoubou. This number will overflow (go back to zero), after approximately 70 minutes. Hook everything up and load the code and then reset the ESP32. Use EEPROM if you still can not solve the issue. This function attempts to provide an accurate delay of at least us microseconds, but it may take longer if the system has other higher priority processing to perform. Since the counter is counting down we subtract it from the current time in milliseconds * 1000. MicroController Posts: 674 Joined: Mon Oct 17, 2022 7:38 pm. This function will start the timer which will trigger every ‘period’ microseconds. Starting at v4. Se estiver utilizando a vTaskDelay, estará evidenciando em seu código a utilização dos recursos do. Sometimes it delays for exactly 2 seconds but sometimes it misses 10ms. We have 10 and 40 microseconds delay requirement for our application development purpose. $endgroup$ – Luke Bayes. Because the change is not just changing. Hi! I need to synchronize 4 esp 32s with an accuracy of 20 microseconds. Returns the number of microseconds since the Arduino board began running the current program.