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Reduce idle cpu consumtion (using the hlt instruction) #53

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copy opened this issue Dec 8, 2023 · 3 comments · May be fixed by #54
Open

Reduce idle cpu consumtion (using the hlt instruction) #53

copy opened this issue Dec 8, 2023 · 3 comments · May be fixed by #54

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@copy
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copy commented Dec 8, 2023

This is a feature request: Currently, when waiting for keyboard input, Mu uses a busy loop (which you can tell by the high CPU usage in qemu, for example in the shell app).

On x86, idling is pretty simple, by using the HLT instruction.
@akkartik
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akkartik commented Dec 8, 2023

The issue here is that Mu doesn't use interrupts yet for the keyboard.. 🤔

@akkartik akkartik linked a pull request Dec 8, 2023 that will close this issue
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@akkartik
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akkartik commented Dec 8, 2023

Ohh, I think I see what you mean! It looks like all my test programs continue to work if I just hlt at the start of every call to read-key! This is the low-level non-blocking primitive and it continues to not block (maybe due to the timer interrupt?) even when I animate say apps/hest-life.mu.

However, when I make this change, running the game of life inside the tiny screen in the shell (following the quickstart and then pressing ctrl+s) slows down a lot. Does that sound right? This isn't insurmountable, I just need to adjust how frequently I check for a keypress when animating.

@copy
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copy commented Dec 8, 2023

However, when I make this change, running the game of life inside the tiny screen in the shell (following the quickstart and then pressing ctrl+s) slows down a lot. Does that sound right? This isn't insurmountable, I just need to adjust how frequently I check for a keypress when animating.

You may need to adjust the PIT reload value. The BIOS default is the maximum, which generates a timer interrupt roughly every 55ms.

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halt until exception when waiting for keyboard akkartik/mu
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@akkartik @copy