Writing to the Framebuffer

Re:Writing to the Framebuffer by Jasper_ on Wednesday April 04, 2018 @06:27PM (#16759857)

Keep in mind that /dev/fb, on a modern system, isn't an actual framebuffer on your GPU. It's a land of make-believe, mostly supported to get the kernel console ("fbcon") working. Going back for at least 10 years, the kernel mode-setting API (KMS) is used to display buffers, and there's compatibility code which sets up a user-space buffer in the KMS subsystem [0] which is swapped to when fbcon happens through a large chain of strange events that are hard to describe. This explains why you can't write to a /dev/fb during an active X11 session and have it show up: it's a fake buffer that only shows up when KMS isn't in use.

[0] https://github.com/torvalds/linux/blob/master/drivers/gpu/dr...

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Re:Writing to the Framebuffer by therein on Wednesday April 04, 2018 @07:43PM (#16760409)

That is correct. One exception perhaps is embedded devices with displays, including EInk tablets.

For instance one thing I have been working on is a library that allows writing to and partially refreshing an EInk display with low latency enabling this[0].

I am curious what would happen if I got xorg working on this and used an additional application to call the `refresh` ioctl so that the changes get displayed on the screen.

[0] https://gfycat.com/CornyHugeIndianRhinoceros

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Re:Writing to the Framebuffer by gandreani on Wednesday April 04, 2018 @09:25PM (#16760972)

That's very awesome! What tablet and project is that?

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Re:Writing to the Framebuffer by therein on Wednesday April 04, 2018 @09:30PM (#16761004)

Thanks. It is the Remarkable Tablet but the API is entirely undocumented. Took a fair bit of analysis to get it to this state but now it is actually ready for people to build their own applications upon it.

The GitHub project: https://www.github.com/canselcik/libremarkable

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Re:Writing to the Framebuffer by codetrotter on Thursday April 05, 2018 @08:34AM (#16764223)

This is cool, you should post it as a “Shown HN”. And don’t get discouraged if it doesn’t immediately garner attention. Post it again later if you only get an insignificant amount of upvotes. Your project is front page worthy and if it doesn’t get there the first time then it’s just bad timing / bad luck (or poorly worded title, that’s a possibility as well of course).

Post it until it gets to the front page, waiting a couple of days or more between each time you post it.

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Re:Writing to the Framebuffer by therein on Thursday April 05, 2018 @01:24PM (#16766887)

Thanks, I am very glad to hear that. I will be posting it with a more detailed write-up soon, detailing the reversing process as well. That should make it an even more interesting read.

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Re:Writing to the Framebuffer by hultner on Thursday April 05, 2018 @08:52AM (#16764380)

I agree, this is super cool and deserves attention.

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Re:Writing to the Framebuffer by therein on Thursday April 05, 2018 @01:24PM (#16766888)

Thank you. :)

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Re:Writing to the Framebuffer by gandreani on Wednesday April 04, 2018 @10:26PM (#16761292)

Thank you very much! I will check out both very soon. I'm interested in a lightweight portable ssh terminal eink device and this combination might just work for me

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Re:Writing to the Framebuffer by hultner on Thursday April 05, 2018 @08:52AM (#16764389)

Oh yes I've been looking for the same thing. Would like something I could connect a keyboard to and attach a tmux session.

Would be a great work machine outside during summer time.

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Re:Writing to the Framebuffer by hultner on Thursday April 05, 2018 @08:51AM (#16764376)

This is super nice, would love to have a tablet like this in the future. Have been experimenting a little bit with my Kobo Glo HD which also got a browser but nowhere close to this.

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Re:Writing to the Framebuffer by tomcooks on Thursday April 05, 2018 @03:44AM (#16762751)

Wow!

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