VHDL support for open-source FPGA toolchain YoSys

ghdlsynth-beta: VHDL synthesis (based on ghdl and yosys )

This is experimental and work in progress!

Build as a module (shared library)

• Get and install yosys .
• Get sources, build and install ghdl . Configure ghdl using at least --enable-libghdl and --enable-synth :

$ ./configure --enable-libghdl --enable-synth
$ make
$ make install

NOTE: GHDL must be built with the latest version of GNAT ( gnat-8 ).

HINT: The default build prefix is /usr/local . Sudo permission might be required to install tools there.

• Get and build ghdlsynth-beta:

make

HINT: If ghdl is not available in the PATH, set GHDL explicitly, e.g.: make GHDL=/my/path/to/ghdl .

The output is a shared library ( ghdl.so on GNU/Linux), which can be used directly:

$ yosys -m ghdl.so

To install the module, the library must be copied to YOSYS_PREFIX/share/yosys/plugins/ghdl.so , where YOSYS_PREFIX is the installation path of yosys. This can be achieved through a make target:

make install

Alternatively, the shared library can be copied/installed along with ghdl:

cp ghdl.so "$GHDL_PREFIX/lib/ghdl_yosys.so"

yosys-config --exec mkdir -p --datdir/plugins
yosys-config --exec ln -s "$GHDL_PREFIX/lib/ghdl_yosys.so" --datdir/plugins/ghdl.so

Build as part of yosys (not recommended)

• Get and build ghdl as in the previous section.

• Get yosys sources.

• Get ghdlsynth-beta and:

  • Patch yosys sources using yosys.diff .
  • Copy src/* to yosys/frontends/ghdl .
  • Configure yosys by adding (to) Makefile.conf :

ENABLE_GHDL := 1
GHDL_DIR := <ghdl install dir>

• Build and install yosys.

Usage

Example for icestick, using ghdl, yosys, nextpnr and icestorm:

cd examples/icestick/

# Analyse VHDL sources
ghdl -a leds.vhdl
ghdl -a spin1.vhdl

# Synthesize the design.
# NOTE: if ghdl is built as a module, set MODULE to '-m ghdl' or '-m path/to/ghdl.so'
yosys $MODULE -p 'ghdl leds; synth_ice40 --json leds.json'

# P&R
nextpnr-ice40 --package hx1k --pcf leds.pcf --asc leds.asc --json leds.json

# Generate bitstream
icepack leds.asc leds.bin

# Program FPGA
iceprog leds.bin

Alternatively, it is possible to analyze, elaborate and synthesize VHDL sources at once, instead of calling ghdl and yosys in two steps. In this example: yosys $MODULE -p 'ghdl leds.vhdl spin1.vhdl -e leds; synth_ice40 --json leds.json .

Docker

Docker image ghdl/synth:beta includes yosys, and the ghdl module (shared library). These can be used to synthesize designs straightaway. For example:

docker run --rm -t \
  -v $(pwd):/src \
  -w /src \
  ghdl/synth:beta \
  yosys -m ghdl -p 'ghdl icestick/leds.vhdl icestick/blink.vhdl -e leds; synth_ice40 -blif leds.blif'

In a system with docker installed, the image is automatically downloaded the first time invoked.

Furthermore, the snippet above can be extended in order to P&R the design with nextpnr and generate a bitstream with icestorm tools:

DOCKER_CMD="$(command -v winpty) docker run --rm -it -v /$(pwd)://wrk -w //wrk"

$DOCKER_CMD ghdl/synth:beta     yosys -m ghdl -p 'ghdl leds.vhdl rotate4.vhdl -e leds; synth_ice40 -json leds.json'
$DOCKER_CMD ghdl/synth:nextpnr  nextpnr-ice40 --hx1k --json leds.json --pcf leds.pcf --asc leds.asc
$DOCKER_CMD ghdl/synth:icestorm icepack leds.asc leds.bin

iceprog leds.bin

NOTE: on GNU/Linux, it should be possible to use iceprog through ghdl/synth:icestorm . On Windows and macOS, accessing USB/COM ports of the host from containers seems not to be supported yet. Therefore, iceprog is required to be available on the host.