ATMEGA2560 clock source switched to Time0 causing chip reset

[DaNanMaoTTT]

Background: I want to reproduce the clock source switching mentioned in tick_sources.md, but I found that the chip resets after running for a few seconds. The project uses Blink_AnalogRead.

[feilipu]

There is quite a bit of modification required to adapt to the ATmega2560 using Timer 0. The best place to start is with my avrfreertos repository that has all the required configuration details included. You will find all the relevant files within the freeRTOS11xx directory. It is worth checking for differences against the Arduino_FreeRTOS library.

Specifically, in the port.c file you will find how to configure the Timer 0 correctly. And the FreeRTOSBoardDefs.h file provides many of the definitions you will need for compiling for the correct hardware. You can trim out the pieces you need specifically for your build and move them to your Arduino_FreeRTOS library files, if you don't mind adapting your library for this specific purpose.

[DaNanMaoTTT]

between https://github.com/feilipu/avrfreertos and https://github.com/feilipu/avrfreertos/tree/master/freeRTOS11xx

[feilipu]

Yes. Arduino_FreeRTOS is built to work within the very limited confines of the Arduino environment. So things like memory management are somewhat crippled.

avrfreertos is built to run standalone, with full access to FreeRTOS capabilities, and there are drivers are written for specific hardware as noted in the repository. It was built together with the Eclipse IDE, though it has been some years since I had a functioning Eclipse system up. It hasn't been a priority.

However, the timer configuration is effectively the same in both cases, as the hardware ATmega2650 is identical.

[feilipu]

is there any difference about two repos?

Specifically, take a difference of the the files mentioned (as well as others in the same branch of the repos) and you will see what needs to be changed to properly use Timer 0 with the ATmega2560.

I would also note that there may be an impact on the ATmega2560 fuse settings. Make sure you've examined those to ensure you're disabling the Watchdog Timer, etc.

[DaNanMaoTTT]

Do I need to define the macros AVR_3_BYTE_PC and AVR_HAVE_RAMPZ on my own? I can't locate them within the library. my board is ATMEGA2560

[feilipu]

Yes, they are needed for proper functioning of the ATmaga2560, which has both a 3 byte PC and the RAMPZ register.

Once you select the MCU type in you compile commands and include the avr header files I believe they will be automatically defined for you.

AVR-libc

If not, you will need to define them, as part of your configuration.