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Programming with an Arduino

Programming the TinyFPGA using an Arduino (or compatible board) is useful in the following cases:

  • You have overridden the TinyFPGA bootloader, so you cannot program the board any more and need a way to upload the bootloader again.

  • You have a project that needs a lot data to be stored in the Flash memory, and leaving the bootloader there takes too much place. In that case, simply upload your bitstream at the address 0 and you are free to use the remaining space.

Hardware

⚠️ The TinyFPGA board is expecting 3.3V, but the Arduino board is typically outputting 5V! We explain below how to go from 5V to 3.3V. ⚠️

The following connections will be made:

Arduino pin TinyFPGA pin Comment
3.3V 3.3V
GND G
10 17 Through 5V-to-3.3V converter
11 14 Through 5V-to-3.3V converter
12 15 Through 5V-to-3.3V converter
13 16 Through 5V-to-3.3V converter

To convert from 5V to 3.3V, a solution is to use a voltage divider made of a few resistors. By using R1=470Ω and R2=1kΩ, we should have an output close to 3.4V, which should be good:

Voltage divider with 2 resistors

If you don't have those specific resistor values, just take the same value three times, the output should be close to 3.3V:

Voltage divider with 3 resistors

The following shows all connections between the two boards:

Overview

⚠️ The TinyFPGA USB port should not be plugged at all at that point, you can plug the Arduino board instead. ⚠️

Uploading the Arduino bootloader with PlatformIO

PlatformIO is an open source ecosystem that make using Arduino and other boards a breathe.

Once installed on your system, start by initialising the project from this directory (using the Arduino UNO board as an example):

$ platformio init --board uno

Then, build the project and upload it to your Arduino:

$ platformio run --target upload

That's all!

Using the Arduino to program the TinyFPGA

We are going to use the programmer CLI.

First, find the vendor and product ID of your Arduino board. Doing so depends on your operating system. For example on GNU/Linux:

$ lsusb
--<snip>--
Bus 001 Device 002: ID 2341:0001 Arduino SA Uno (CDC ACM)
--<snip>--

Now, use that vendor-product ID to program the Flash via the Arduino:

$ ../programmer/tinyfpgab.py -d 2341:0001 -a 0 -p /snip/bootloader.bin

Notice the following in the command above:

  • The -d parameter specifies the device ID (vendor:product)
  • The -a parameter gives the address at which to program the bitstream: here we are writing at address 0, which is the correct address to put the TinyFPGA bootloader at.

Depending on the bitstream run by the FPGA, you may need to do the following:

  • Disconnect the Arduino from your computer, plug it back, and try again
  • Do the same, but this time press the reset button once before programming
  • Do the same, but this time hold the reset button before programming and during the whole programming operation: it is likely to last a minute or two, so be patient or use some non-metallic tool to hold the reset button down (a wooden clothes peg seems to do the job)