Docs: Add fud registration instructions for Interpreter (#2138)

* Add fud registration instructions

* Put invoke tip in debugger page too

* Ref cells and not invokes are cider's problem

docs/debug/cider.md

@@ -6,17 +6,25 @@ debugging Calyx programs.
 
 ## Getting Started
 
-If you are using [`fud`][fud] getting started with the debugger is easy.
+If you are using [`fud`][fud], getting started with the debugger is easy.
+
+First, follow [these instructions][interp-fud] to build the interpreter and register it as a `fud` stage.
+
 Assuming you are trying to debug a program called `my_program.futil` with data
 file `my_program.futil.data`, invoke the debugger with the following command:
 
 ```
 fud e --to debugger -q my_program.futil -s verilog.data my_program.futil.data
 ```
 
-This will open the target program in the interactive debugger. Note that `fud`
-uses **the quiet flag**, `-q`, here. This prevents the printing from the `fud` tool
-from conflicting the debugger as both tools interact with standard out.
+This will open the target program in the interactive debugger. Note that we use `fud`'s *quiet* flag, `-q`, here. This avoids clashes between `fud`'s outputs and the debugger's outputs, since both tools interact with `stdout`.
+
+The interpreter does not currently support [`ref` cells][ref-cells].
+To run the debugger on a program that uses these, you must first compile them away by running the `compile-invoke` pass:
+
+```
+fud e --to debugger -s calyx.flags '-p compile-invoke' -q my_program.futil -s verilog.data my_program.futil.data
+```
 
 ## Advancing Program execution
 
@@ -280,3 +288,5 @@ Use `help` to see all commands. Use `exit` to exit the debugger.
 [fud]: ../running-calyx/fud/index.md
 [gdb]: https://sourceware.org/gdb/
 [interp]: ../running-calyx/interpreter.md
+[interp-fud]: ../running-calyx/interpreter.md#interpreting-via-fud
+[ref-cells]: ../lang/memories-by-reference.md#the-easy-way-ref-cells

docs/running-calyx/interpreter.md

@@ -22,7 +22,11 @@ The interpreter is available as a stage in [fud][], which lets you provide stand
 
 You'll want to build the interpreter first:
 
-    cd interp && cargo build
+    cd interp && cargo build && cd ..
+
+Now register the interpreter as a fud stage:
+
+    fud config stages.interpreter.exec <full path to Calyx repository>/target/debug/cider
 
 Here's how to run a Calyx program:
 
@@ -42,4 +46,8 @@ For example, to fully lower the Calyx program before interpreting it:
         -s calyx.flags '-p all' \
         interp/tests/control/if.futil
 
+In particular, the interpreter does not currently support [`ref` cells][ref-cells].
+To run the interpreter on a program that uses these, you must first compile them away by running the `compile-invoke` pass.
+
 [fud]: fud/index.md
+[ref-cells]: ../lang/memories-by-reference.md#the-easy-way-ref-cells