![]() While it looks the same at the C source level, it will not generate the same instructions as a register a lower address such as 'H' or lower bit set/clear instructions not supported for any register above G.įor example on a Atmega 1280/2560 PORTK |= 0b00000001 This one can trip up even and advance user. PORTB |= 0b00000001 Īlso, not all AVR registers support bit set and bit clear instructions. This second example is also much slower than doing each bit separately which sets each bit atomically.īut while each bit is set atomically, there is no way on an AVR to set multiple bits in a register atomically without setting all the bits in the register. This second example of attempting to set multiple bits can cause register corruption if an ISR is also modifying PORTB. Some AVRs have registers, including i/o port registers that are outside of the range that supports bit set/clear instructions.Īs a result, if interrupts are involved or multiple bits are being set/cleared or there is an attempt to set a single bit in a register that is outside the supported range it is possible that an attempt to set/clear bits can result in register corruption.Ĭompiles into a single atomic SBI instruction with no concerns when using with ISR code that also modifies PORTB bits. it can only atomically set/clear a single bit and even when it can, the address range that this can be done is very limited. This is because the AVR has very limited capabilities when it comes to setting and clearing bits. Some forms of malfunction can be not so obvious, particularly to less experienced code writers and there are some cases than can trip up even advanced users. It should also be noted that there can be atomicity issues when using AVR raw port i/o. use that downtime to adjust the duty cycle "most of the time" (processor-wise) the above do nothing as the proper time hasn't elapsed PreviousMicros = previousMicros + highTime PreviousMicros = previousMicros + lowTime Įlse if ((elapsedMicros >= highTime) & (highLow = 1)) If ((elapsedMicros >= lowTime) & (highLow = 0)) LowTime = period - highTime // with numbers above, 10000 - 1000 = 9000ĮlapsedMicros = micros() - previousMicros Unsigned long highTime = 1000UL // microsecondsīyte highLow = 0 // flag to show which state output is in Obviously, PINB won’t compile on another board so I was looking for alternative ways to handle it. The pot referenced below adjusts the duty cycle which is interpreted by the device to adjust position.” Analogwrite support PWM is 490hz and 900hz.” So, I need the100hz signal but I’d rather not use an UNO since I have other stuff to combine running on another board. The issues, are: The pwm signal for the device I’m trying to drive has a a built in circuit that uses a fixed 100hz frequency with varying duty cycle from 10%-90%. I wanted to understand the what and how first so I could understand how to modify it for another board. That thread was closed so I can’t ask there. That is significantly faster! So, this code below is where it was used. Some replace a slow Arduino board with a fast Arduino board, but if a sketch is full with delay(), then it will be just as slow. The millis() function can be used to do multiple things at the same time. To make a sketch faster, you should remove all the delay() and check if the libraries use delay(). Writing code that will work only on one specific microcontroller is not very productive (although Arduino allows you to do so). To blink a led every second, there is not need to be fast. Some think that it is a good thing to be faster, but it is not, it is very bad to use fancy incompatible code. ![]() A lot, but that is irrelevant if you have to ask.No, this is low-level register access, which Arduino allows you to use if you want.It does not translate to a Teensy, unless the direct register commands of the Teensy are used. PINB is the input port of Port B which is associated with 8 pins.Using the registers of a microcontroller directly is faster.Using a register called "PINB" which is only available for certain boards breaks with that rule. The main goal of Arduino is to provide a common set of functions that will work on every Arduino board. ![]() However, all the low-level commands are also available and even assembly code can be added.
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