MegaCoreX is Arduino compatible out of the box, but also includes extra functionality that's not available on the official Arduino "megaavr" core. This is functionality that I personally have been missing in the official Arduino API, and have added to MegaCoreX instead.
My goal isn't to "Arduino wrap" all hardware functionality the megaAVR-0 series brings to the table, but to expose functionality advanced users may benefit from and actually use. If you have a very niche application that utilizes one of the more obscure features the chip has, you're probably better off writing the low-level code yourself. Very spesific needs for ADC readings? Obscure timer needs? Read the approperiate Microchip application note w!
The default analog read resolution for these chips is 10 bit, which gives you values between 0 - 1023. If you need lower resolution you can turn it down to 8 bits instead, which gives you values between 0 - 255.
Simply call analogReadResolution like this:
analogReadResolution(8); // Set resolution to 8 bits
analogReadResolution(10); // Set resolution to 10 bitsFor timing critical applications the standard digitalRead() and digitalWrite() functions may be too slow. To solve this, MegaCoreX also includes some improved variants that compiles down to a single instruction.
Call digitalReadFast(myPin) or digitalWriteFast(mypin, state) to use these.
Note that the pin number and pin state has to be known at compile time!
uint8_t digitalReadFast(uint8_t pinNumber);
void digitalWriteFast(uint8_t pinNumber, uint8_t state);The megaAVR-0 microcontrollers support alternative pin assignments for some of their built-in peripherals.
This is specified by invoking the swap() or pins() method before begin() for the associated peripheral.
They will return true if that swap or pin combination is supported.
For Serial peripherals the method is pins(tx,rx), for Wire it's pins(sda,scl) and for SPI it's pins(mosi,miso,sck,ss).
(Note that this is the same pin sequence as used for the ESP8266 pins method, but the opposite of the one SoftwareSerial uses.)
Note that swap() and pins() do the exact same thing, but swap() is MUX swap oriented, while pins() is pin oriented.
If you want to use this feature to implement communication with two different external devices connected to different pins using one internal peripheral,
note that the proper way to switch is first to invoke end() to cleanly shut down, then swap() or pins() to switch assigned pins, and finally begin() to cleanly start again.
swap() or pins() are called like this. Use either swap() or pins(), not both!
// UART pin swapping
Serial3.swap(1);
Serial3.begin(9600);
// Wire pin swapping
Wire.swap(1);
Wire.begin();
// SPI pin swapping
SPI.swap(1);
SPI.begin();Available pin combinations for the 48 pin standard pinout are:
| Peripheral | Default | Alternative 1 | Alternative 2 |
|---|---|---|---|
| Serial | swap(0) or pins(0,1) | swap(1) or pins(4,5) | |
| Serial1 | swap(0) or pins(14,15) | swap(1) or pins(18,19) | |
| Serial2 | swap(0) or pins(34,35) | swap(1) or pins(38,39) | |
| Serial3 | swap(0) or pins(8,9) | swap(1) or pins(12,13) | |
| Wire | swap(0) or pins(2,3) | swap(1) or pins(16,17) | |
| SPI | swap(0) or pins(4,5,6,7) | swap(1) or pins(14,15,16,17) | swap(2) or pins(30,31,32,33) |
Available pin combinations for the 28 pin and 32 pin standard pinouts are:
| Peripheral | Default | Alternative |
|---|---|---|
| Serial | swap(0) or pins(0,1) | swap(1) or pins(4,5) |
| Serial1 | swap(0) or pins(8,9) | |
| Serial2 | swap(0) or pins(20,21) | swap(1) or pins(24,25) |
| Wire | swap(0) or pins(2,3) | swap(1) or pins(10,11) |
| SPI | swap(0) or pins(4,5,6,7) | swap(1) or pins(8,9,10,11) |
Available pin combinations for the Uno WiFi pinout are:
| Peripheral | Default | Alternative |
|---|---|---|
| Serial | swap(0) or pins(27,26) (connected to mEDBG) |
swap(1) or pins(9,10) |
| Serial1 | swap(0) or pins(1,0) | swap(1) or pins(32,33) (available on SPI header) |
| Serial2 | swap(0) or pins(24,23) (connected to Wifi module) |
swap(1) or pins(2,7) |
| Serial3 | swap(0) or pins(6,3) | swap(1) or pins(37,38) (not broken out) |
Available pin combinations for the Nano Every pinout are:
| Peripheral | Default | Alternative |
|---|---|---|
| Serial | swap(0) or pins(25,24) (connected to USB-serial chip) |
swap(1) or pins(9,10) |
| Serial1 | swap(0) or pins(1,0) | swap(1) or pins(34,35) (not broken out) |
| Serial2 | swap(0) or pins(2,7) | swap(1) or pins(28,27) (not broken out) |
| Serial3 | swap(0) or pins(6,3) | swap(1) or pins(37,38) (not broken out) |
pinConfigure is a template based function that exposes all functions that can be configured on a per-pin basis. The first argument is the Arduino pin number to configure, and the second to nth parameter are the configuration parameters. The order the arguments has does not matter. The function will set the pin functionality regardless if it "makes sense" or not. If you enable interupts on a pin and there's no interrupt handler in your code, the microcontroller will crash.
template <typename... MODES>
void pinConfigure(const uint8_t digital_pin, const pin_configure_t mode, const MODES&... modes);// Set pin PA0 to output and drive the pin high
pinConfigure(PIN_PA0, PIN_DIR_OUTPUT, PIN_OUT_HIGH);
// Disable pin PA1 completely to save power
pinConfigure(PIN_PA1, PIN_INPUT_DISABLE);The following parameters ca be used to set the pinConfigure modes:
| Functionality | Enable | Disable | Toggle |
|---|---|---|---|
| Direction, pinMode() | PIN_DIR_OUTPUTPIN_DIR_OUTPIN_DIRSET |
PIN_DIR_INPUTPIN_DIR_INPIN_DIRCLR |
PIN_DIR_TOGGLEPIN_DIRTGL |
Pin output, HIGH or LOW |
PIN_OUT_HIGHPIN_OUTSET |
PIN_OUT_LOWPIN_OUTCLR |
PIN_OUT_TOGGLEPIN_OUTTGL |
| Internal Pullup | PIN_PULLUP_ONPIN_PULLUP |
PIN_PULLUP_OFFPIN_NOPULLUP |
PIN_PULLUP_TGL |
Invert HIGH and LOW |
PIN_INVERT_ON |
PIN_INVERT_OFF |
PIN_INVERT_TGL |
| Digital input buffer | PIN_INPUT_ENABLE orPIN_ISC_ENABLE |
PIN_ISC_DISABLE orPIN_INPUT_DISABLE |
Not supported |
| Interrupt on change | PIN_ISC_ENABLE orPIN_INPUT_ENABLE |
PIN_ISC_ENABLE orPIN_ISC_DISABLE |
Not applicable |
| Interrupt on Rise | PIN_ISC_RISE orPIN_INT_RISE |
PIN_ISC_ENABLE orPIN_ISC_DISABLE |
Not applicable |
| Interrupt on Fall | PIN_ISC_FALL orPIN_INT_FALL |
PIN_ISC_ENABLE orPIN_ISC_DISABLE |
Not applicable |
| Interrupt on LOW | PIN_ISC_LEVEL orPIN_INT_LEVEL |
PIN_ISC_ENABLE orPIN_ISC_DISABLE |
Not applicable |
Unlike the official Arduino core, MegaCoreX has printf support out of the box. If you're not familiar with printf you should probably read this first. It's added to the Print class and will work with all libraries that inherit Print. Printf is a standard C function that lets you format text much easier than using Arduino's built-in print and println.
Note that the default printf implementation will NOT print floats or doubles by default. This is a limitation of the avr-libc printf implementation on AVR microcontrollers, but can be enabled by setting a build flag. This can easily be done if you're using PlatformIO.
If you're using a serial port, simply use Serial.printf("Milliseconds since start: %ld\n", millis());. Other common libraries that inherit the Print class (and thus supports printf) are SoftwareSerial, the LiquidCrystal LCD library and the u8g2 graphical LCD library.