[dv] dvsim -t xrun enhancement

[svenka3]

Today I tried running OT on a different laptop with Cadence XLM tool. I made small mistakes (call it rusted due to out of touch with OT flow) and one of them is:

 util/dvsim/dvsim.py -t xrun hw/ip/uart/dv/uart_sim_cfg.hjson -i uart_smoke -r 1

I was sure that -t was wrong, but wanted to see what happens and I got:

INFO: [dvsim] [proj_root]: /home/srini/proj/OpenTitan/Git_OT_Google/opentitan
CRITICAL: [utils] Failed to parse "/home/srini/proj/OpenTitan/Git_OT_Google/opentitan/hw/dv/tools/dvsim/xrun.hjson" possibly due to bad path or syntax error.
[Errno 2] No such file or directory: '/home/srini/proj/OpenTitan/Git_OT_Google/opentitan/hw/dv/tools/dvsim/xrun.hjson'

How about 2 enhancements:

1. Add xrun as some sort of alias to xcelium - as more users are familiar with the term xrun (and is easier to type :-) )
2. dvsim can give better error message here.

Thanks

[sriyerg]

Will probably take the option 2 route.

[rswarbrick]

I think we've intentionally avoided dvsim having a list of known simulators. But we could probably do something like check for a file that should exist for a supported simulator, and give a helpful error message if it doesn't. Here, it would be something like hw/dv/tools/dvsim/{tool}.hjson.

[rswarbrick]

I've taken another look, and a tidier error message would be quite difficult. As things stand, dvsim's Python code doesn't know anything about known tools. In fact, the tools/dvsim/{tool}.hjson file gets included by common_sim_cfg.hjson, so the Python code itself doesn't even know the directory where it expects the file to exist.

The current behaviour looks like this:

$ util/dvsim/dvsim.py hw/top_earlgrey/dv/chip_sim_cfg.hjson --tool=foo
INFO: [dvsim] [proj_root]: /home/rjs/work/opentitan
CRITICAL: [utils] Failed to parse "/home/rjs/work/opentitan/hw/dv/tools/dvsim/foo.hjson" possibly due to bad path or syntax error.
[Errno 2] No such file or directory: '/home/rjs/work/opentitan/hw/dv/tools/dvsim/foo.hjson'

and I'm not so sure there's something cleaner that we can do, without somehow encoding a "blessed" list of tools in the Python code itself.

[svenka3]

Thanks. To an external user such as me, maintaining a "blessed" list of tools in a large project such as OT makes perfect sense, I would understand if your team does not buy-in to that, however.

How about adding an extra line as:

util/dvsim/dvsim.py hw/top_earlgrey/dv/chip_sim_cfg.hjson --tool=foo
INFO: [dvsim] [proj_root]: /home/srini/proj/OpenTitan_Git/ot_rpro/opentitan
CRITICAL: [utils] Maybe an unsupported/incorrect tool option is specified as -t
Failed to parse /home/srini/proj/OpenTitan_Git/ot_rpro/opentitan/hw/dv/tools/dvsim/foo.hjson possibly due to bad path or syntax error.
[Errno 2] No such file or directory: '/home/srini/proj/OpenTitan_Git/ot_rpro/opentitan/hw/dv/tools/dvsim/foo.hjson'

I tweaked/hacked utils.py to be:

 except Exception as e:
        msg = "Maybe an unsupported/incorrect tool option is specified as -t \n"
        msg += "Failed to parse " + hjson_file + " possibly due to bad path or syntax error.\n" + str(e)
        log.fatal(msg)

[rswarbrick]

Oof. I've just done a little bit of digging here and things are rather complicated.

The path to the tool-specific path gets inferred from the tool value when expanding common_sim_cfg.hjson. So the dvsim code itself doesn't really know that this particular import comes from --tool.

What's more, the common_sim_cfg.hjson file gets included explicitly by all the blocks, so the dvsim tool doesn't theoretically even know how --tool gets translated to "an hjson file that must exist".

I can think of two possible "right answers":

1. Make dvsim a little more constrained and teach it that an hjson file whose name is based on --tool must always exist in some particular place. That would solve this problem, but it's rather ugly and potentially stops dvsim becoming more configurable in the future.
2. Add (yet another) new hjson key, which allows the user to give something like a map from include path to error message. That would allow common_sim_cfg.hjson to say "if {tool}.hjson doesn't exist, complain about the --tool argument".