TinyUPDI

What is tinyUPDI?

The tinyUPDI is a tiny programmer uses for programming any AVR that supports SerialUPDI interface. Unlike other UPDI programmers, it only requires one USB port and automatically switches between UPDI programming and debugging serial mode.

Why did you make it?

Many modern AVR developers in the past, we included, hacks together a USB Serial adaptor with a few components together for programming UPDI-capable AVR chips. Those hacks work as a UPDI programmer, it is however in reality often requires another USB/UART ports for serial debugging printout. The tinyUPDI supports automatic switch between UPDI and UART interfaces via a single USB port, saving the needs for connecting two USB ports.

What makes it special?

• Single USB port connection supports both UPDI and debugging Serial Monitor
• Supports all UPDI-programmable AVRs
• Supports Arduino IDE and PlatformIo development envrionment
• Works with multiple Arduino Cores such as megaTinyCore, DxCore and should  MegaCoreX
• Based on latest CP2101N from Silicon lab.
• No USB driver required for macOS, Windows and Linux (kernel v2.6.12 onward)
• Capable of powering target board (5v only) directly via the 6-pin programming header from USB power source

Working with megaTinyCore/DxCore

Arduino IDE

Instead of using the SerialUPDI implementation pymcuprog.py from Microchip, megaTinyCore/DxCore ships with its own version of SerialUPDI, When working with Arduino IDE, any of the SerialUPDI options in Tools -> Programmers would work with tinyUPDI. However, when using modes higher than 230400bps, it occasionally failed or in the case of running at 921600bps, the underneath programming function failed to read the data correctly and will fallback to 115200bps. We recommend to use the options for baudrate of 230400bps for the best performance between speed and reliablity.

Arduino IDE with Apple Silicon

The tinyUPDI works well under the Windows, Linux and MacOS in general. However, when using it with MacOS Apple Silicon machines, it does not output data to the Serial Monitor of Arduino IDE for some unknown reason. One workaround is to use an external terminal software such as [CoolTerm](CoolTerm - Download where DTR state can be set, this works but is not seemless as you would need to disconnect the terminal before the programming.

Another altertive is to use PlatformIO as your IDE environment which provide better user experience between progamming mode and serial debugging mode.

PlatformIO

tinyUPDI works well under PlatformIO with megaTinyCore with proper configuration.

Install pymcuprog

The build-in programmer that is tightly integreated with megaTinyCore and works well with Arduino IDE, but not with PlatformIO. We recommend to download and install the pymcuprog from Microchip.

Configure PlatformIO.ini

Here is an example of platformio.ini configuration for running an Attiny3227 at 20MHz on a MacOS:

[env:ATtiny3227]
board = ATtiny3227
platform = atmelmegaavr
framework = arduino
board_build.f_cpu = 20000000L
monitor_speed = 115200
monitor_rts = 0

upload_protocol = custom
upload_port = /dev/cu.usbserial* ; for MacOS
upload_speed = 230400

; for using pymcuprog, download and install it via PyPi
upload_flags =
    --tool
    uart
    --device
    $BOARD
    --uart
    $UPLOAD_PORT
    --clk
    $UPLOAD_SPEED
upload_command = pymcuprog write --erase $UPLOAD_FLAGS --filename $SOURCE

The monitor_rts = 0 flag is only required when operating under MacOS with Apple Silicon, it ensures the terminal would activated upon opening correctly.

Working with MegaCoreX

Unfortunately at this moment, we don't have any MCU chip/board running with MegaCoreX with us to test the tinyUPDI but we think it very likely should work without any extra issue other than what we covered here. We will provide an update of this section once we have the chance to test it.