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Old 18 December 2014, 17:49   #1
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Lightbulb [Suggest] Display FPU: x%


In some case i would like to verify if the FPU is in use, for instance to check which apps make use of the fpu, if present, and when.

I don't think it's possible atm. Is it feasible ?

By the way, as i'm new here, i take the opportunity to thank you for your hard word
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Old 19 December 2014, 11:00   #2
Toni Wilen
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It can't work very well because AmigaOS task scheduler always uses some FPU instructions (to store/restore FPU context) when FPU is available.
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Old 19 December 2014, 11:42   #3
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oh, sad. i undestand. no filtering specific task possible ? hmm, complicated, and maybe superslow. ho well...
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Old 20 December 2014, 19:36   #4
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Wonder if it would be possible within the emulation framework to report similar to CPU usage? That way, it would be understood that standard AOS usage would always report a low percentage, but when running a more FPU-intensive program then it would be obvious based on the percentage that the program itself was making good use of the FPU. Alternately, perhaps a threshold that's high enough to filter out system FPU usage but still be triggered when something more FPU-intensive is running. By FPU-intensive I mean like the countless '881 builds of popular software such as Imagine, VistaPro, etc.

Alternately, maybe it would be possible to use AOS-side software to do this? I know that some software can report CPU usage (I remember this feature from DOpus among others). Perhaps a small piece of AOS software could serve the same purpose? Also alternately, maybe even a combination of AOS software along with host-side code to present the information outside the emulated Amiga window (so that it would be present in the emulation window no matter which screen is frontmost, nor which windows are present on said screen).
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Old 21 December 2014, 16:09   #5
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Yes, maybe amigaos side tool but what toni said about task scheduler will still be true.
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Old 21 December 2014, 17:02   #6
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The CPU-usage of a task is calculated with the help of the multitasking scheduler. There are sleeping tasks, tasks waiting in the ready state and one running task which is using the CPU for a limited period, a time slice. The scheduler uses the task priorities to decide which of the waiting tasks comes next to get the CPU. So the CPU-usage of a task depends on the time it is in the running state in relation to the overall time.

But there is no FPU scheduler. FPU instructions are just some special commands that the running task can make use of. Of course it would be possible to count the access to any FPU instruction and set it in relation to the standard CPU instruction calls. But this would only make sense for an optional debug mode, because it will probably cause a big slowdown.

If you only want to know whether a program uses the FPU then simply disassemble it and scan for the mathlib strings or for FMOVE, FADD, FMUL instructions etc. Use your editor and count the occurrences of these or other Fxxx commands.
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