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Using the code below, the clock is set for 80 MHz. Here are some results for the interrrupt interval for various values in MAP_TimerLoadSet(). Have I setup something wrong?
Load Measured Expected
320 249.25 KHz 250 KHz
160 497 KHz 500 KHz
80 823 KHz 1 MHz
40 821 KHz 2 MHz
Hi John,
I think the explanation is very similar to where I answered you in the other post. https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1088930/ek-tm4c123gxl-unexpected-performance-limit
The timer you configure uses the system clock as the clock source running at 80Mhz. You have the preload value equal to 40. This means every 40 system clock cycles it will generate an interrupt. In your interrupt, you perform several operations. Below is the disassembly code of Timer0IntHandler(). As you can see it take quite some instructions to execute the ISR. There is also some latency from the time the interrupt is triggered by the timer module until the processor enters the ISR. All of these will exceed 40 cycles. In your measurements, you measure about the same for both 40 and 80 as the preload value. You can try 4Mhz or higher and you will be measuring similarly as in 2Mhz and 1Mhz because the number of cycles to execute the ISR and the latency to enter the ISR is independent of the interrupt interval you configure. Normally, you would like to keep the ISR as simple as possible. This is what RTOS does for the interrupt handling. You can try to just set a flag in the ISR. In the main code, base on the flag to process your inputs (e.g. set and clear the LED) and then clear the flag.
