[RFC] DisplayDevice for t1rocket emulation

[OceanS2000]

Depends on #800 , this PR contains followup DisplayDevice implementation.

Currently it simply dumps a fixed-size RGB buffer to disk as png upon writing to a control register. The specific interfaces are open to futher discussion.

[OceanS2000]

done

…

On Mon, Oct 28, 2024 at 7:35 AM Jiuyang Liu ***@***.***> wrote: ***@***.**** requested changes on this pull request. ------------------------------ In nix/t1/conversion/sv-to-verilator-emulator.nix <#815 (comment)>: > - verilatorThreads = 8; + verilatorThreads = 4; nit ------------------------------ In nix/t1/mill-modules.nix <#815 (comment)>: > setupSubmodulesEditable - mill mill.bsp.BSP/install 0 ''; nit — Reply to this email directly, view it on GitHub <#815 (review)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AHHUSA4WJX763PK66DYD2CLZ5XSNDAVCNFSM6AAAAABQM5BUS2VHI2DSMVQWIX3LMV43YUDVNRWFEZLROVSXG5CSMV3GSZLXHMZDGOJYGE2TEMZSGA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[FanShupei]

When I test it locally, unfortunately it won't pass the offline check.

Reproduction steps:

1. run nix build -L --impure .#t1.rookidee.t1rocketemu.run.disp.simple.vcs-emu
2. check result/offline-check-journal, it shows following error

thread 'main' panicked at offline_t1rocketemu/src/json_events.rs:208:7:
rtl data(0x1) should be equal to board data(0x0)
stack backtraces:
...

[FanShupei]

There's no error in your code. It's a known limitation in our difftest framework.

Our offline verifier currently has no knowledge of mmio devices, it treats every read/write as regular memory access. We could add side effects for mmio read/write in our online simulation framework, but we must preserve load value axiom (the value loaded must equal to the last store to the same address). The frame counter read-back feature violates this, so the offline verifier complains loudly.

[OceanS2000]

As a temporary measure I removed all read operation of counter from simple.c

[FanShupei]

LGTM now.