The development side. Compiling and simulating your Verilog/VHDL can be done with open source software, but to put it on the FPGA itself, you generally need closed source (and sometimes paid) tools to generate the bitstreams. Contrast that with microcontrollers such as the ATMega which can be programmed from start to finish using an entirely FOSS stack - even the bootloader and programmer. And for some reason, these companies consider the bitstream formats trade secrets and refuse to document them at all.
1) vivado webpack edition (ie free) lets you write (and flash) a bitstream for some of the small chips. i know it at least works for the artix-7 family because i'm doing it every day lately
2) for the artix-7 (and some lattice chips) you supposedly can use OSS (https://github.com/SymbiFlow/prjxray). i haven't tried it yet but one problem i can foresee is that the OSS tools won't infer stuff like brams and dsp. in fact the symbiflow people (i think?) explicitly call this out as the part of the project that's a work in progress.
>Lattice has been by far the favorite of the FOSS community
i'm interested in the OSS flows but i haven't dug in yet. so some questions (if you have experience): isn't it only for their ice40 chips? and how smooth is the flow from RTL to bitstream to deploy?
one hesitation i have with jumping in is that i'm working on accelerator type stuff, so my designs typically need on the other of 30k-50k LUTs. will yosys+nextpnr let me deploy such a design to some chip?
