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ekiwi / wellen

wellen: waveform datastructures in Rust. Fast VCD, FST and GHW parsing for waveform viewers.
BSD 3-Clause "New" or "Revised" License
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Add support for VHDL boolean type #16

Closed augustofg closed 5 months ago

augustofg commented 6 months ago

Hi Kevin,

It seems that wellen doesn't support VHDL boolean typed signals, when trying to view the bool signal after loading the attached file, surfer crashes:

[INFO] Loading a waveform file: /tmp/vhdl_test_bool.fst
[INFO] Returning from perform work
[INFO] Starting async task
[INFO] Loaded the hierarchy and meta-data of /tmp/vhdl_test_bool.fst in 16.397565ms
[INFO] FST file loaded
[INFO] Returning from perform work
[INFO] Starting async task
[INFO] Loaded the body of /tmp/vhdl_test_bool.fst in 16.545957ms
[INFO] Returning from perform work
[INFO] Starting async task
The application panicked (crashed).
Message:  Unexpected signal value: false
Location: /home/augusto/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wellen-0.9.9/src/fst.rs:186

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.

You have my permission to include the attached fst file to the regression test suit.

Thanks for the great work you are doing. Augusto.

vhdl_test_bool.fst.zip

ekiwi commented 6 months ago

Thanks for reporting! I am a bit busy at the time, but I will try to investigate over the next couple of weeks.

ekiwi commented 5 months ago

Could you tell me more about which simulator is produced this file? Looks like a variable is declared as a 1-bit value, but then gets a string false as value change.

I will try to see how I can get this to work.

augustofg commented 5 months ago

Hi Kevin,

This file was generated with NVC from what I remember. I can try with GHDL to see how it will behave.

Augusto.

On June 11, 2024 5:26:47 PM GMT-03:00, Kevin Laeufer @.***> wrote:

Could you tell me more about which simulator is produced this file? Looks like a variable is declared as a 1-bit value, but then gets a string false as value change.

I will try to see how I can get this to work.

-- Reply to this email directly or view it on GitHub: https://github.com/ekiwi/wellen/issues/16#issuecomment-2161551804 You are receiving this because you authored the thread.

Message ID: @.***>

ekiwi commented 5 months ago

Thanks for the info. Yes, I would be curious to see what GHDL produces.

augustofg commented 5 months ago

Indeed, GHDL seems to produce a FST file that can be opened with surfer with no problems. I've attached both FST files and the VHDL source used to generate those.

Strangely, gtkwave can open and visualise the NVC generated FST, but have problems with the GHDL FST.

vhdl_test_bool_nvc.fst.gz vhdl_test_bool_ghdl.fst.gz vhdl_test_bool.tar.gz

ekiwi commented 5 months ago

I added a small workaround in the latest wellen release (0.9.11). It won't look super pretty, since it will essentially turn boolean signals into a 1-bit bit-vector signal, but its something that could be done without completely refactoring wellen. nvc could always switch to do "the right thing", i.e. encode booleans as a FST enum.

nickg commented 5 months ago

I'm a bit confused by this because NVC should emit booleans identically to other enums except with FST_SDT_VHDL_BOOLEAN instead of FST_SDT_NONE.

ekiwi commented 5 months ago

I'm a bit confused by this because NVC should emit booleans identically to other enums except with FST_SDT_VHDL_BOOLEAN instead of FST_SDT_NONE.

OK. Then I will try to have a closer look at what is going on.

ekiwi commented 5 months ago

@nickg can you point me to the code in nvc that generates the hierarchy entry for boolean variables?

nickg commented 5 months ago

https://github.com/nickg/nvc/blob/f2118b2d189bb50392f9d65b8ca57cd07f085708/src/rt/wave.c#L327

All enums are emitted as strings at the moment (FST_VT_GEN_STRING). I can't remember why I'm not using FST_VT_SV_ENUM. Possibly I couldn't get it to work with GtkWave.

ekiwi commented 5 months ago

All enums are emitted as strings at the moment (FST_VT_GEN_STRING). I can't remember why I'm not using FST_VT_SV_ENUM. Possibly I couldn't get it to work with GtkWave.

Thanks for all the info @nickg! I think I have a better way of dealing with this issue now.

ekiwi commented 5 months ago

I have a much better fix now. Turns out that I the type of a variable in a VCD or FST does double duty: (1) it indicates how the signal is supposed to be encoded (string, real or bit-vector) (2) it informs the user what the type of the variable in the original HDL code was. This overloading combined with the additional VHDL type information lead to wellen discarding the correctly declared String encoding from nvc. That is fixed now in the 0.9.12 release. Thanks a lot @nickg and @augustofg !