![]() To wrap up with delay I can read frequencies from 1 to 494 Hz, but with delayMicroseconds I can only read 30 to 10000 Hz. However, the highest number I can use with delayMicroseconds is 16383 which gives me a frequency of around 30 Hz, so no chance of getting the frequencies from 2 to 29 Hz. delayMicroseconds(490) = 999 Hz at the flow computer If I use the delayMicroseconds () command then I can get the higher frequencies but not the lower ones I achieve with delay() However I would like to get a step up and simulate higher frequencies, up to 10000 Hz. Code samples in the reference are released into the public domain. The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. I Set/Clear them at regular intervals using the delay command and when I connect them to the microcontroller I read a frequency (Hz).Īll good so far, using the delay command I can read frequencies up to 494 Hz, with the delay 1 microseconds. Corrections, suggestions, and new documentation should be posted to the Forum. The simulator uses 2 parallel pulses (A and B), when A is on B is off and viceversa. I am trying to create a pulse simulator for a microcontroller. You can of course stop interrupts before calling delayMicroseconds() and enable them afterwards, but that again does impact timing accuracy by the duration of compiled code for enabling/disabling.Hi all, I'm quite new at this so sorry if I am asking silly questions. When an interrupt is received during the execution of the delayMicroseconds(), the timing of delayMicroseconds() will be wrong. "brne 1b" : "=w" (us) : "0" (us) // 2 cyclesīTW: The compiled code is pretty accurate, but be aware of the following: On Arduino there are timed interrupts configured that most are unaware of. account for the time taken in the preceeding commands. per iteration, so execute it four times for each microsecond of the following loop takes a quarter of a microsecond (4 cycles) ![]() of the function call yields a delay of approximately 1 1/8 us. ![]() for a one-microsecond delay, simply return. for the 16 MHz clock on most Arduino boards 2 microseconds) gives delays longer than desired. calling avrlib's delay_us() function with low values (e.g. Since theyre unsigned longs, the maximum value is 232 - 1, or 4294967295, so if millis ()/micros () is less than the last snapshot taken, the millis ()/micros () value has wrapped to zero and we have to subtract the last. Calling _asm_-code from C requires some extra instructions to save CPU registers.įor a normal Arduino only the following code will be compiled: /* Delay for the given number of microseconds. The first two lines are there to deal with the fact that millis () and micros () will wrap around to zero after a while. The last -2 microseconds (before the loop is kicked off) is again a correction on compiler introduced overhead. 16MHz/(4×4) = 1MHz, which takes 1 us cycle time, the resolution that we are after. ![]() The _asm_-loop compiles into a 4 CPU cycle loop. Then the delay value is multiplied by four ( <<=2). That an assumption of the author! The number of CPU cycles 'burnt' by each instruction is well documented in the Atmel AVR instruction set document.įirst the delay value is checked for being equal to 1, in that case just returning from the routine already spent over a microsecond of CPU time. ![]() The code heavily relies on compiler optimization being exactly the same for you as for the developer of the library. For now just focus on this single function, it doesn't rely on any other fucntions.īy inspecting the code you'll notice that it is not about timers, it is all about instruction cycles. Take the effort of finding the file and browsing through it. Windows systems will have a similar path to the wiring.c file. The source code for this function is fairly well documented and can be found in /usr/share/arduino/hardware/arduino/cores/arduino/wiring.c on Linux systems. ![]()
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