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# MachXO2 Architecture Example
This contains a simple example of running `nextpnr-machxo2`:
* `simple.sh` generates JSON output (`{pack,place,pnr}blinky.json`) of a
classic blinky example from `blinky.v`.
* `simtest.sh` will use `yosys` to generate a Verilog file from
`{pack,place,pnr}blinky.json`, called `{pack,place,pnr}blinky.v`. It will
then and compare `{pack,place,pnr}blinky.v`'s simulation behavior to the
original verilog file (`blinky.v`) using the [`iverilog`](http://iverilog.icarus.com)
compiler and `vvp` runtime. This is known as post-place-and-route simulation.
* `mitertest.sh` is similar to `simtest.sh`, but more comprehensive. This
script creates a [miter circuit](https://www21.in.tum.de/~lammich/2015_SS_Seminar_SAT/resources/Equivalence_Checking_11_30_08.pdf)
to compare the output port values of `{pack,place,pnr}blinky.v` against the
original `blinky.v` _when both modules are fed the same values on their input
ports._
All possible inputs and resulting outputs can be tested in reasonable time by
using `yosys`' built-in SAT solver or [`z3`](https://github.com/Z3Prover/z3),
an external SMT solver.
As `nextpnr-machxo2` is developed the contents `simple.sh`, `simtest.sh`, and
`mitertest.sh` are subject to change.
## How To Run
Each `sh` script runs yosys and nextpnr to validate a blinky design in various
ways. The `mode` argument to each script- `pack`, `place`, or `pnr`- stop
`nextpnr-machxo2` after the specified phase and writes out a JSON file of the
results in `{pack,place,pnr}blinky.json`; `pnr` runs all of the Pack, Place,
and Route phases.
`mitertest.sh` requires an additional option- `sat` or `smt`- to choose between
verifying the miter with either yosys' built-in SAT solver, or an external
SMT solver.
To keep file count lower, all yosys scripts are written inline inside the
`sh` scripts using the `-p` option.
To clean output files, run: `rm -rf *.dot *.json *.png *.vcd *.smt2 *.log {pack,place,pnr}*.v blinky_simtest*`
## Environment Variables For Scripts
* `YOSYS`- Set to the location of the `yosys` binary to test. Defaults to the
`yosys` on the path. You may want to set this to a `yosys` binary in your
source tree if doing development.
* `NEXTPNR`- Set to the location of the `nextpnr-machxo2` binary to test.
Defaults to the `nextpnr-machxo2` binary at the root of the `nextpnr` source
tree. This should be set, for instance, if doing an out-of-tree build of
`nextpnr-machxo2`.
* `CELLS_SIM`- Set to the location of `machxo2/cells_sim.v` simulation models.
Defaults to whatever `yosys-config` associated with the above `YOSYS` binary
returns. You may want to set this to `/path/to/yosys/src/share/machxo2/cells_sim.v`
if doing development; `yosys-config` cannot find these "before-installation"
simulation models.
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