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megaTinyCore (sometimes "mTC" informally) - Arduino support for all tinyAVR 0/1/2-Series

Questions? Cases where you don't know whether the problem is in your code or the core? Things to show off?

We have a Github Discussions section now. When a problem is definitely a defect in the core, you will reduce the time taken to fix it if you create an issue, as I prioritize issues over catching up on discussions.

2.6.8 is out - rejoice

This corrects many of the bugs present in 2.6.x

2.6.x introduces improved flash footprint of serial significantly while adding features, wire can wake slave from sleep without corrupting data, and much, much more, see the Changelog.

IMPORTANT WARNINGS

ATTN: Linux Users

Only versions of the Arduino IDE downloaded from arduino.cc should be used, NEVER from a linux package manager. The package managers often have the Arduino IDE - but have modified it. This is despite their knowing nothing about Arduino or embedded development in general, much less what they would need to know to modify it successfully Those version are notorious for subtle but serious issues caused by these unwise modifications. This core should not be expected to work on such versions, and no modifications will be made for the sake of fixing versions of the IDE that come from package managers for this reason.

IDE Versions 2.0.x and some 2.1 do not work correctly

This is a bug in the Arduino client.

IDE versions between 1.8.13 and 2.x developed significant novel defects. IDE versions 1.8.2 and earlier , however, possess crippling unfixed defects. I believe that they finally have a working version of the IDE out, and I believe that latest is able to install my core correctly.

Prior to megaTinyCore 2.6.0, manual installation of megaTinyCore would cause V1.8.14 of the IDE to crash due to this bug when you install the core manually in your arduino folder. Users of 1.8.14 and later must use version 2.6.0 of megaTinyCore.

Don't Buy Modern AVRs (Anything this core supports) on AliExpress or From eBay International Sellers

I buy a lot of electronics stuff on AliExpress. It's a great marketplace for things that are made by Chinese companies and are mostly generic, including loads of components unavailable to individuals in the global West any other way (ex, min order is a reel or something like that - if you can even find a component vendor that works with the no-name chinese chip maker). It is not a great place for the latest semiconductor product lines from major Western manufacturers, especially in the midst of a historic shortage of said chips. The modern AVR devices, when they are available through those channels at all, are frequently reported to be fake or defective (like ATtiny412s that think they're 416s and may not correctly execute power on reset). For that matter, you probably don't want to buy any AVR microcontrollers on AliExpress... Assembled boards, like Arduino Nano clones, generally work if you avoid the ones with the third party LGT8 chips and watch out for the ones with the ATmega168p instead of the '328p - but there are a lot of reports of bogus microcontrollers when they're sold as bare chips (I have heard of fake ATtiny85s that were actually remarked ATtiny13s; it's not just modern AVRs that get faked). There are a lot of interesting theories for where those bogus chips came from, and Microchip has remained totally silent on the issue.

Using This Document

This document is best viewed online (as opposed to opening the markdown file in your favorite text editor), so that links are clickable and inline images are shown, and probably most importantly, to make tables render correctly sometimes. Again, this [document can be found on github](https://github.com/SpenceKonde/megaTinyCore]

Getting Started

Wiring

Installation

Arduino 1.8.13 is strongly recommended

Older versions do not properly handle the programmers in the tools -> programmers menu, which degrades the UX rapidly as the number of installed cores increases. They are not suitable. The newest versions starting with 1.8.14 (including 1.8.17, 1.8.18, and 1.8.19) may generate a "panic: no major version found" error because they fail to properly parse platform.txt. Since 2.6.0 we have been manually modifying the platform.txt directly before release, so this is less of an issue

When megaTinyCore is installed through board manager, the required version of the toolchain is installed automatically. All 0/1/2-Series parts are supported with no extra steps. Up until 2.2.7, we used Arduino7 version of avr-gcc (gcc 7.3.0 and avrlibc 3.6.1) with latest ATpacks as of june 2020. Starting with 2.2.7, we began using my Azduino build of the toolchain, which has updated ATpacks for all the newly supported parts. 2.2.7 used Azduino3, 2.3.0+ used Azduino4, and starting with 2.6.0, we use Azduino5 (though it offers no benefit for us, other than saving a quarter GB of HDD space and 40mb of download bandwidth if you install both megaTinyCore and DxCore through board manager.

Manual installation is more complicated - particularly if you want support for the 2-Series; see the Installation guide for more information.

megaTinyCore - Background and Basics

An Arduino core for the tinyAVR 0-Series, 1-Series, and now the 2-Series. These parts have an improved architecture compared to the "classic" tinyAVR parts (which are supported by ATTinyCore), with improved peripherals and improved execution time for certain instructions (these are similar in both regards to the advanced AVR Dx-Series, as well as megaAVR 0-Series chips like the ATmega4809 as used on the official Nano Every and Uno Wifi Rev. 2 - although the Arduino team has done their best to kneecap them) in the low-cost, small packages typical of the ATtiny line. All of these parts feature at least one hardware UART, and an SPI and TWI interface (none of that USI garbage like, for example, the ATtiny85 has), a powerful event system, configurable custom logic, at least one on-chip analog comparator, a surprisingly accurate internal oscillator, and in the case of the 1-Series, an actual DAC output channel, and in the case of the 2-Series, a fancy differential ADC.

Moreover, the tinyAVR 0/1/2-Series parts are cheap - the highest end parts, the 3226 and 3227, with 32k of flash and 3k of SRAM (vs the 2k SRAM as the ATmega328p used in Uno/Nano/ProMini) run just over $1 USD in quantity - less than many 8k classic AVR ATtiny parts ("AVR instruction set, at a PIC price"). All of these parts are rated to run at 16 MHz or 20 MHz (at 4.5-5.5v) without an external crystal, and the internal oscillator is accurate enough for UART communication.

These use UPDI programming, not traditional ISP like the classic ATtiny parts did. See below for more information. Getting a UPDI programmer is simple - you can use a classic 328p-based Arduino as programmer using jtag2updi - or for better results with cheaper hardware, you can use any USB-serial adapter and a resistor (and preferably a diode) using the included SerialUPDI tool, or you can use AVRdude with one of the Microchip programmers (the mEDBG/nEDBG/EDBG-based programmers on their development board, Atmel-ICE or SNAP) or any UPDI programming tool that emulates one of those (which, to my knowledge, all of them do - if there is one that avrdude supports and that my core doesn't, please open an issue to let me know!).

A serial bootloader, Optiboot_x (based on the same codebase as the classical Arduino Uno bootloader, though since greatly altered) is supported on these parts (0/1-Series support is currently live, 2-Series is expected by the first week of May; adjustments for the new parts are trivial), allowing them to be programmed over a traditional serial port. See the Optiboot section below for more information on this, and the relevant options. Installing the bootloader does require a UPDI programmer. The assembled breakout boards I sell on Tindie are available pre-bootloaded (they are bootloaded on demand). That being said the user experience with Optiboot is a little disappointing on the 0/1-Series parts as well as the 14-pin 2-Series parts, due to their lack of a hardware reset pin that could be used with the usual autoreset circuit to automatically reset into the bootloader when the serial port is opened. You need to either disable UPDI programming entirely (requiring an HV programmer if fuse settings or bootloader need to be change after initial bootloading) or leave UPDI enabled, but start any upload within 8 seconds of applying power. The 20-pin and 24-pin 2-Series parts support an "alternate reset pin" allowing these to act more like a traditional Arduino.

UPDI Programming

The UPDI programming interface is a single-wire interface for programming (and debugging - Universal Programming and Debugging Interface), which is used used on the tinyAVR 0/1/2-Series, as well as all other modern AVR microcontrollers. While one can always purchase a purpose-made UPDI programmer from Microchip, this is not recommended when you will be using the Arduino IDE rather than Microchip's (godawful complicated) IDE. There are widespread reports of problems on Linux for the official Microchip programmers. There are two very low-cost alternative approaches to creating a UPDI programmer, both of which the Arduino community has more experience with than those official programmers.

From a USB-Serial Adapter With SerialUPDI (pyupdi-style - Recommended)

Before megaTinyCore existed, there was a tool called pyupdi - a simple Python