Project IceStorm: open-source toolchain for Lattice iCE40 FPGAs

I'm on my first foray into FPGA development, using IceStorm as the toolchain for a Lattice iCE40 FPGA (iCE40HX4K) to implement a system controller for my homebrew 6502 single board computer. The FPGA is (work in progress) doing clock management, address decoding, memory bank switching, SPI comms, some GPIO, and bootstrap to RAM from SPI flash memory.

It's fantastic having an open-source toolchain! It's why I chose the Lattice iCE40, and perhaps what got me over the line to even try FPGA development; the closed proprietary tools are very off-putting to new starters. I had previously dabbled with a Xilinx FPGA dev board, but spent most of my time battling the giant Xilinx ISE toolchain.

Big thanks to Claire Wolf for creating IceStorm and making FPGA dev more accessible to software engineering types like me.

Aside (cc: dang?) I think http://bygone.clairexen.net/icestorm/ is the newer/better canonical URL for IceStorm, since the creator changed their name, as linked to from their projects page at https://www.clairexen.net/projects and mentioned at the bottom of the current http://www.clifford.at/icestorm/ page.

I was led to this work because of the fomu [1]. Also, if you're familiar with the Precursor [2] you'll realize the second, smaller fpga inside is the iCE40 as well (which makes sense, the same people responsible for tomu/fomu are involved with the precursor).

[1] https://tomu.im/fomu.html

[2] https://www.crowdsupply.com/sutajio-kosagi/precursor

Despite the last entry on the linked page being in 2018, the source repository shows that it is an active project.

https://github.com/YosysHQ/icestorm

From memory (simple?) VHDL is supported by using gHDL as a synthesis engine, the output of which can feed into the yosys/icestorm tool chain?

https://ghdl.github.io/ghdl/using/Synthesis.html

https://github.com/ghdl/ghdl-yosys-plugin

Seems this page hasn't been updated in a while. People interested in open source FPGA toolchains might be better off starting at https://symbiflow.github.io/ which is the umbrella project (of which icestorm is a part), and is more up to date.

The current project is known as SymbiFlow[1][2], it includes IceStorm and many other things.

[1] https://symbiflow.github.io/

[2] https://github.com/SymbiFlow/

Around 15 years ago, the micro controller world was as proprietary as the FPGA is today. Arduino won. We're fighting the same battle this time and I hope we'll win again.

The experience of a toolchain actually working correctly and not crashing all the time will be a disorienting experience for people coming from the proprietary FPGA toolchains.

I've been following the IceStorm project for a while and it's some really impressive work. Now if only we could get a decent open source SystemVerilog simulator to go along with it. As someone who works in the ASIC design world, the thing that makes my side projects die out is usually the state of the open source simulation tools. I have tried to use both Verilator and Icarus, and both have so many limitations and quirks beyond what I'm used to with the commercial tools gave up on them.

I keep telling myself I need to dig into their source code and start fixing problems, but going from user to developer on these kinds of tools is a big jump.

Claire Wolf is fucking brilliant!

P.S. formal verification is like crack when you get your first try, be wary...

I learned the FPGA ropes by making (from scratch, reinventing many wheels) a fast interface between dbus (TI calculator link port) and a standard serial port in Verilog. It is dramatically faster than every other "link cable" available.[1]

Thanks to IceStorm/yosys/nextpnr, I never had to touch a proprietary tool to do this.

There's now very cheap, OSHW development boards to get started with[2].

[1] https://github.com/rvalles/dbus_ti_link_uart_verilog

[2] https://joelw.id.au/FPGA/CheapFPGADevelopmentBoards

I played around with Risc-V on this platform. Super easy and fun.