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How ISR is serviced?
An interrupt service routine (ISR) is a software routine that hardware invokes in response to an interrupt. ISR examines an interrupt and determines how to handle it executes the handling, and then returns a logical interrupt value. If no further handling is required the ISR notifies the kernel with a return value.
Why are timer interrupts important?
Each occurrence of a timer interrupt triggers the following major activities: Updates the time elapsed since system startup. Updates the time and date. Determines how long the current process has been running on the CPU and preempts it if it has exceeded the time allocated to it.
Why does my ISR not have enough time to run?
As pointed out by @ReAI, your ISR does not have enough time to run. Your ISR will take more than 1 microsecond to execute and return, so you always are missing interrupts. There are other problems here too. For example, your microsecondsTimervariable is accessed in both the ISR and the foreground and is a long.
How often does the ISR run on timer0?
Now your ISR only runs once every 256 microseconds and when it runs, it need only increment a “microseconds * 256” counter in each call.
Why does the ISR always take more than 1 microsecond?
Your ISR will take more than 1 microsecond to execute and return, so you always are missing interrupts. There are other problems here too. For example, your microsecondsTimervariable is accessed in both the ISR and the foreground and is a long. longvariables are 4 bytes wide and so are not updated atomically.
Is there a microsecond timer implemented on timer0?
There is Attiny85, with an internal clock source at 8 MHz. I am trying to implement a microsecond timer based on the hardware timer timer0. What is my logic:Since the clock frequency is 8 MHz and the prescaler is off, the time of one clock cycle will be about 0.1us (1/8000000).