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Writing an OS in Rust: Introduction to Paging

os.phil-opp.com

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Re: Writing an OS in Rust: Introduction to Paging

#41

Post by nostrademons »

jstimpfle wrote: post #3

I've never programmed in Rust because I still have trouble seeing the point. It seems overly restrictive. A copy of any data has nearly zero marginal cost (and you can pay the cost by doing the work yourself), so in a free machine, it would have nearly zero price. If widely useful data is protected by the borrow checker, far fewer people will use it. It is easy to show that the total utility of a piece of data to the…

"To counter the borrow checker, I'm currently designing a programming language featuring a mechanism that grants free access to data structures, with the restriction that copiers must grant the same rights to anyone else:"

So....C? GNU makes so much sense now!

Re: Writing an OS in Rust: Introduction to Paging

#42

Post by gshack »

renholder wrote: post #33
JesseWright wrote: post #2

I've followed Phil's site on making an operating system. Ever since having worked on PintOS in college, operating systems and their internals have fascinated me. I've tried learning more about writing operating systems via resources like the OSdev wiki, but much of its material almost seems to discourage working on an OS of any kind unless you're already sure of what you're doing. Phil's articles seems so much more a…

Same here. Especially MenuetOS[1], because it was written in Assembly and originally fit on a floppy disk. That's a level of patience and programming (in Assembly) that I can only admire from afar... [1] - https://en.wikipedia.org/wiki/MenuetOS

Holy heck, it's still in active development

Re: Writing an OS in Rust: Introduction to Paging

#44

Post by sidcom »

SlowRobotAhead wrote: post #17
fermienrico wrote: post #4

As a side note: I wish Rust would come to embedded development ASAP running a real time OS written in Rust. You can use massive Boost libraries and Qt frameworks on non-embedded systems with C/C++, but in embedded, there is no such luxury. I am new to it but it is painful and I wish to see a day where we have a complete LLVM based ARM compiler toolchain with Rust sitting on top. I think there were some blog posts abo…

Get used to the idea that embedded is 15 years behind PC. Which is initially frustrating but if you step back is kind of a good thing. I’d also like to see Rust make it’s way into embedded. C support for things like data serialization or RPC for interfacing to web stuff is limited, people just don’t port it to C. And C++ doesn’t thrill me in terms of its non-deterministic garbage handling and difficult to debug natur…

Non deterministic garbage handling doesn't sound right in combination with C++. You have to do it your self. And you can make it deterministic.

Re: Writing an OS in Rust: Introduction to Paging

#45

Post by anyfoo »

simias wrote: post #26
JesseWright wrote: post #2

I've followed Phil's site on making an operating system. Ever since having worked on PintOS in college, operating systems and their internals have fascinated me. I've tried learning more about writing operating systems via resources like the OSdev wiki, but much of its material almost seems to discourage working on an OS of any kind unless you're already sure of what you're doing. Phil's articles seems so much more a…

I think it's one of these things that's more approachable if you start by working on specific subsystems of an existing OS. This way you don't have to figure everything out at once. At least that's how I did it. I think writing an OS from scratch is discouraging and not very accessible because... writing an OS is discouraging and not very accessible. It's a bit as if a painter was saying "It tried looking up guides o…

I agree.

By the way, you mention high impedance and metastabilty. Knowing next to nothing about the PlayStation, are those concepts relevant for emulation there for some reason? For other platforms I think that’s an abstraction layer that even accurate emulators rarely hit (though I might be wrong). Is there something special on the PlayStation?

Re: Writing an OS in Rust: Introduction to Paging

#48

Post by grawprog »

ivl wrote: post #39
simias wrote: post #26

Earlier quoted context omitted.

I think it's one of these things that's more approachable if you start by working on specific subsystems of an existing OS. This way you don't have to figure everything out at once. At least that's how I did it. I think writing an OS from scratch is discouraging and not very accessible because... writing an OS is discouraging and not very accessible. It's a bit as if a painter was saying "It tried looking up guides o…

To your comment about a PlayStation being ridiculously simple compared to a desktop computer I'd call that close to true in the case of the now 20 year old first generation. The most recent two have basically been custom extensions on top of an operating system (FreeBSD 9). Which is to say they are desktop computers.

I generally assume if there's no numbers appended to the end of PlayStation it's referring to the PlayStation 1. Also, based on the context of what the parent poster was describing, I think it's fairly safe to assume they were in fact referring to the 'first generation' Playstation as you call it.

Re: Writing an OS in Rust: Introduction to Paging

#50

Post by simias »

anyfoo wrote: post #45
simias wrote: post #26

Earlier quoted context omitted.

I think it's one of these things that's more approachable if you start by working on specific subsystems of an existing OS. This way you don't have to figure everything out at once. At least that's how I did it. I think writing an OS from scratch is discouraging and not very accessible because... writing an OS is discouraging and not very accessible. It's a bit as if a painter was saying "It tried looking up guides o…

I agree. By the way, you mention high impedance and metastabilty. Knowing next to nothing about the PlayStation, are those concepts relevant for emulation there for some reason? For other platforms I think that’s an abstraction layer that even accurate emulators rarely hit (though I might be wrong). Is there something special on the PlayStation?

It's been a while since I've looked into it so I hope I won't be too far off the mark:

- Regarding high impedance it might be relevant if you want to explain how the controller and memory card interface works, and why you read full 1s when nothing is connected (high impedance line with a pull-up resistor). More generally the issue will crop up every time you have an interface that might be floating, I think people who have no background in electronic engineering might assume that unconnected wire == 0 on the line.

- Regarding metastability it crops up in the timers. The PSX timers can either run from the CPU clock or from signals coming from the GPU (pixelclock and horizontal blanking). IIRC this is used in some lightgun games to be able to synchronize the signal coming from the gun ("I saw the lightbeam") with the current position of the pixel in the frame currently being sent to the TV set.

The problem with that is that the signals coming from the GPU are not synchronous with the CPU and apparently are not resynchronized. That creates metastability issues when the value from these timers are read from the CPU and you may end up reading bogus values from time to time. The software workaround is to read the register values in a loop until you get twice the same value in row. Now, you probably don't need to emulate that but if you want to be thorough it's probably worth pointing out.

So in summary you're right, you don't really need to know that in order to write a proper PSX emulator but if you really want to get into all the details you'll probably want to brush the subject. At least these are concepts that anybody is sure to encounter eventually is they spend time in bare-metal land...

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