Re: [Qemu-devel] [Bug 1239008] Re: qemu fails to scroll screen on ^Vidmem output

[rjasmin <1239008@bugs.launchpad.net>]

I dont know how to write it myself, but the original kernel scrolling 
code is in C.
Might try OSDev forums. Not that I know of.

On 11/27/2013 09:24 PM, Serge Hallyn wrote:
> Thanks for reporting this bug.  Is there any other reproducer you can
> give us?
>
> ** No longer affects: kvm (Ubuntu)
>
> ** Also affects: qemu (Ubuntu)
>     Importance: Undecided
>         Status: New
>
> ** Changed in: qemu (Ubuntu)
>         Status: New => Incomplete
>
> ** Changed in: qemu
>         Status: New => Incomplete
>

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https://bugs.launchpad.net/bugs/1239008

Title:
  qemu fails to scroll screen on ^Vidmem output

Status in QEMU:
  Incomplete
Status in “qemu” package in Ubuntu:
  Incomplete

Bug description:
  Pascal uses ^Vidmem for B800 console output. The terminal does not
  oblige the Pascal OS code to scroll the output. Virtualbox emulation
  works, so this must be a qemu bug. Using QEMU in KVM mode as Ubuntu
  LTS.

  Source line to trip bug(in theory pushes VideoMem up one line):

  procedure Scroll;
  //this is whats causing crashes. FIXME:Virtualbox not affected.QEMU BUG?
  begin
    if scrolldisabled then exit;
        if (CursorPosY >= 24) then begin  //in case called before end of screen
      blank:= $20 or (TextAttr shl 8);
      Move((VidMem+(2*80))^,VidMem^,24*(2*80));
      // Empty last line
      FillWord((VidMem+(24*2*80))^,80,Blank);
      CursorPosX:=1;
      CursorPosY:=23;
      update_cursor;
    end;
  end;

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