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Old 20 January 2019, 22:07   #1
Code Kitten

Join Date: Aug 2015
Location: Montreal/Canadia
Age: 48
Posts: 1,143
Tools (and hardware) for latency measurement in Amiga emulators?

Hello kittens,

I recall seeing a few talks here and there on the EAB regarding emulation latency measurements but I do not recall them ever mentioning tools and/or hardware explicitly designed to measure emulation latency.

(Also, note that I am fully aware of the recent WinUAE video latency improvements, I followed and participated a bit to these discussions. But this is not what this is about.)

Are you aware of any such setup which would allow precise, objective measurements of input-to-video latency?

Ideally, they would come packaged as a combo of:
- AmigaDos executable which would wait for keyboard/joystick/mouse input and immediately display the result on screen in different manners: immediate background color register change, VBL synced color change.
- An instrumented Amiga emulator (WinUAE, macOS/Windows FS-UAE, whatever) composed of:
- An external program with proper OS privileges which generates input events corresponding to the emulator input (DX buttons/keyboard on Windows, other on macOS) and writes down the timestamp at which said events are generated.
- An emulator modified to
1- immediately notify to that external program the corresponding color register change (gives an idea of the internal latency of the emulator)
2- reproduce on a second window and with the same timings as the original emulated Amiga window, the color changes of the targeted color register. This one allows external hardware to plug onto the screen and detect the color change as it happens on the display)
- A hardware device which connects to the host computer and does:
- send a start signal for the external program to issue the input events to the emulator
- plugs a small sensor on a dedicated portion of the screen where the emulator displays a window filled with the color of the target color register value, and measure the precise timing at which color changes happen.

The idea behind that setup would be that it would allow to precisely and objectively measure internal and external latencies and eliminate indirect measurement methods (i.e., videotape keyboard and screen while the user presses a key which is highly imprecise).

I am aware of some threads here discussing about latency but I do not know and have not been able to find if there were initiatives dedicated to building such a setup.
My software and hardware background tells me that both hardware and software would not be that difficult to write. Moreover, such hardware could be reused for any other thusly instrumented emulator.

Does anyone know if any such initiative is currently ongoing in the retro world?
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