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Re: No scrolling for long input lines

From: Vesa Jääskeläinen
Subject: Re: No scrolling for long input lines
Date: Wed, 08 Oct 2008 19:40:38 +0300
User-agent: Thunderbird (Windows/20080914)

Andy Goth wrote:
> "Andy Goth" <address@hidden> wrote:
>> I'll test the current SVN this Friday, or perhaps Thursday night at
>> the earliest.
> Actually I did spend time tonight investigating.  I needed to get the latest 
> SVN for another reason (about which I have questions I'll ask in a few days), 
> so I went ahead and looked into my scrolling input problem.
> Yup, still there.  Today's SVN is affected.
> The problem is present when actually booting using GRUB (ordinary VGA text 
> mode), but it all works fine in grub-emu.
> Wait, I take that back.  In grub-emu, typing very long lines (that wrap and 
> *cause the screen to scroll*) results in the text wrapping at column 80 
> instead of column 79, so that there is *not* a white space character in the 
> rightmost column.  Pressing Ctrl-U from such a line will only erase only the 
> bottom line of text, except for the first six characters (which presumably 
> correspond to "grub> ").
> Something's flaky!  However, this grub-emu stuff might be unrelated to the 
> problem I've been having with the actual boot loader.
> I also add that in grub-emu, the carriage doesn't return after printing an 
> error message, so I get a stairstep effect.  With such an indented prompt, 
> issuing a command like "ls" causes output to be printed to the *left* of the 
> prompt.
> Enough about grub-emu.  In the actual boot loader, I noticed that the pattern 
> seems to be: it will scroll the screen if inserting text will cause the last 
> character to overflow the right edge of the screen.  That sounds like the way 
> it should be, right?  The problem is that only currently visible characters 
> appear to be checked for overflow.  This doesn't include the character being 
> typed or characters that previously have failed to scroll onscreen.
> Test cases:
> 1. Near the top of the screen, type a bunch of text and overflow the edge.  
> Works fine.
> 2. Hold down enter until the screen starts scrolling.  Works fine.
> 3. Type a bunch of text and overflow the edge.  Fails to scroll!
> 4. Use the left arrow key one or two times and type text.  Fails to scroll!
> 5. Use the left arrow key until the cursor is onscreen, and type text.  
> Everything scrolls into view.
> I'd absolutely love to debug all this and provide patches, but I really don't 
> have time right now.  In fact I didn't have time to do the research I did; I 
> should have been sleeping. :^(

This seems to be BIOS issue in a way. In startup.S
grub_console_real_putchar there is quite good comment about what are
BIOS limitations.

Choices are to modify this code here, or make better bios console terminal.

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