Arduino core files for MCUdude's cores

This repo contains the Arduino corefiles used with MightyCore, MegaCore, MiniCore and MajorCore.

Supported devices

• ATmega640, ATmega1280, ATmega2560
• ATmega64, ATmega128, ATmega1281, ATmega2561
• AT90CAN32, AT90CAN64, AT90CAN128
• ATmega8535, ATmega16, ATmega32, ATmega164A/P, ATmega324A/P/PA/PB, ATmega644/P, ATmega1284/P
• ATmega8515, ATmega162
• ATmega8, ATmega48/P/PA/PB, ATmega88/P/PA/PB, ATmega168/P/PA/PB, ATmega328/P/PA/PB
• ATmega165/A/P/PA, ATmega325/A/P/PA, ATmega645/A/P
• ATmega3250/A/P, ATmega6450/A/P
• ATmega169/A/P/PA, ATmega329/A/P/PA, ATmega649/A/P
• ATmega3290/A/P, ATmega6490/A/P

Supported clock frequencies

By supported I mean clocks that accurate timing is implemented for (millis, micros, delay, delayMicroseconds).

• 32 MHz
• 25 MHz
• 24 MHz
• 22.1184 MHz
• 20 MHz
• 18.432 MHz
• 18 MHz
• 16.5 MHz
• 16 MHz
• 14.7456 MHz
• 12 MHz
• 11.0592 MHz
• 10 MHz
• 9.216 MHz
• 8 MHz
• 7.3728 MHz
• 6 MHz
• 4 MHz
• 3.6864 MHz
• 2 MHz
• 1.8432 MHz
• 1 MHz

Adding further clock frequencies

The calculation of millis(), micros() and delay() is automatic for arbitrary frequencies. Depending on the prime factors of the frequency, it is either exact or approximate to 60 ppm accuracy (worst-case). The only thing required is adding support in delayMicroseconds().

Exactness of delayMicroseconds()

The delayMicroseconds(unsigned int us) implementation is exact up to a few cycles for the frequencies listed above.

The maximum input parameter to work reliably is 10000 for 10 milliseconds. Its result is affected by interrupts occurring, which may prolong the delay.

Exactness of micros() and delay()

For the clock speeds listed above, micros() is corrected to zero drift. Even for very long run times, the micros() function will precisely follow the oscillator used.

Frequencies not listed above are either exact or corrected to below 60 ppm drift and in exact sync with millis().

Note that the result of micros() may jump up by several microseconds between consecutive calls and rolls over after one hour and eleven minutes.

The delay() function uses micros() internally and inherits its drift accuracy with slight variations due to function call overhead and processing. It is immune to interrupts and thus long-term accurate.

Exactness of millis()

For the clock speeds listed above, millis() is corrected to zero drift. Even for very long run times, the millis() function will precisely follow the oscillator used.

Frequencies not listed above are either exact or corrected to below 60 ppm drift and in exact sync with micros() and delay().

We do not register the rollover of the unsigned long millis counter that occurs every 49.7 days; such would have to be done in the user's program. Often this is not necessary: The code

if (millis() - millis_old >= interval) {
  /* do something */
  millis_old += interval;
}

is long-term accurate even when rolling over provided millis_old is of type unsigned long.

For clock speeds of 16 MHz and below, the return value of millis() occasionally jumps up by more than one (notwithstanding low/zero drift). Thus, when relying on consecutive returns, run at 16.5 MHz or higher.