Cider: The Calyx Interpreter & Debugger

Cider resides in the interp/ directory of the repository. Cider supports all Calyx programs—from high-level programs that make heavy use of control operators, to fully lowered Calyx programs. (RTL simulation, in contrast, only supports execution of fully lowered programs.)

There are two ways to use the interpreter: you can directly invoke it, or you can use fud2. The latter is generally recommended.

Basic Use

To run an example program, try:

cd interp && cargo run tests/control/if.futil

You should see something like:


This output contains some header information and the raw binary data of the memories in the program and as such is not human readable. A separate tool, cider-data-converter is used to parse this dump into a human readable json and vice versa. Once you've compiled it, either by running cargo build in tools/cider-data-converter or by running cargo build --all, you can run:

cargo run tests/control/if.futil | ../target/debug/cider-data-converter --to json

which should produce

  "mem": [

You can see the available command-line options by typing cargo run -- --help.

Interpreting via fud

The interpreter is available as a stage in fud2, which lets you provide standard JSON data files as input and easily execute passes on the input Calyx program before interpretation.

You'll want to build the interpreter and compiler first:

cargo build && \
cd interp && cargo build && \
cd ../tools/cider-data-converter && cargo build && cd ../../

or just run

cargo build --all

Once you've installed and configured fud2 you can run the same program by invoking

fud2 tests/control/if.futil --to dat --through cider -s

Data is provided in the standard Calyx json and fud2 will automatically handle marshalling it to and from Cider's binary format, outputting the expected result. Note that fud2 requires a provided data file, so in cases where you do not initialize memory you will still need to provide the initial state of the memories. Such files can be generated via the data gen tool or you can invoke Cider directly to bypass this constraint.

By default, fud will not transform the Calyx code before feeding it to the interpreter. To run passes before the interpreter, use the calyx.flags variable in conjunction with the -p flag. For example, to fully lower the Calyx program before interpreting it:

fud2 --to dat --through cider \
    -s calyx.flags='-p all' \
    -s \

Cider outputs

By default, Cider's output memory dump will only contain the @external memories on the entrypoint component. If you want to see other memories in the main component, the flag --all-memories will force Cider to serialize all memories. For prototyping, it can occasionally be useful to serialize registers as well, this can be done by passing the flag --dump-registers which will cause Cider to serialize all registers in the main component as single entry memories.