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Hi,

Can anyone point me to a tutorial which explains how paging can be achieved using 80x25 text mode from protected mode?

I need to implement scrolling for up to 8 pages.

Thanks

Simple, keep a backbuffer somewhere else in the kernel's memory, and use memcpy to scroll.

Thanks but I was hoping for a less memory consumptive solution.

I think I read somewhere that 8 pages (one page = 80*25) can be addressed from 0xb8000 and it's possible to send I/O commands to have the VGA controller select different pages to display. Is this possible?

Actually if there is way via ports to select pages, that anyway it is slower than memcpy (or memmove). In 80x25 mode displayed just 80*25 words. If you'll find way to change buffer address - great, but I guess all of us use simple memmove.

jasonc122 wrote:I think I read somewhere that 8 pages (one page = 80*25) can be addressed from 0xb8000 and it's possible to send I/O commands to have the VGA controller select different pages to display. Is this possible?

Yes, but that only does full-page scrolling, not line-at-a-time. For the latter (or if you want more than 200 lines total, even less if you're doing multiple terminals like Linux can) you'll need to use memcpy; besides, a 4K memcpy isn't even going to be noticed, even with a 1-byte-at-a-time copy.

Besides, storing the text separately and using memcpy makes it much easier to change to using a framebuffer console (80*25 text on a big screen is quite annoying, especially when a framebuffer console can probably get at least three or four times that in each dimension depending on screen size)

Selenic wrote:

jasonc122 wrote:I think I read somewhere that 8 pages (one page = 80*25) can be addressed from 0xb8000 and it's possible to send I/O commands to have the VGA controller select different pages to display. Is this possible?

Yes, but that only does full-page scrolling, not line-at-a-time.

Wrong!

Combuster wrote:

Selenic wrote:

jasonc122 wrote:I think I read somewhere that 8 pages (one page = 80*25) can be addressed from 0xb8000 and it's possible to send I/O commands to have the VGA controller select different pages to display. Is this possible?

Yes, but that only does full-page scrolling, not line-at-a-time.

Wrong!

Oh, interesting. That also allows (theoretically) 128K of characters, which is still a 16K buffer per terminal for eight virtual terminals (which I think is a very nice feature to have)

Either way, framebuffers are even better, IMHO, because you can then mix graphics in really easily, and changing video mode doesn't screw everything up.