48 lines
2.5 KiB
Plaintext
48 lines
2.5 KiB
Plaintext
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This file describes the nature of DBCS support in ntldr/setupldr.bin for x86.
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On non-x86 machines we do nothing for now. The firmware is in control of the video
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and thus the firmware is supposed to support displaying characters deemed necessary
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by the system designer.
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The x86 loaders operate using either standard 80x25 vga text mode or standard
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640x480 graphics mode. In the latter case the loader display system paints
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characters to simulate a console-type environment. Text mode is the default.
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Early in initialization, the loader attempts to open a file called BOOTFONT.BIN
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on the root of the drive from which boot is occurring (ie, in the same place where
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it later expects to find ntdetect.com, boot.ini, etc). If that file is found and
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is deemed valid, the display subsystem switches to graphics mode and is thus able
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to display arbitrary glyphs. The font file gives such details as the dbcs lead byte
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ranges, and so support in the loader display system is not dependent on any
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particular codepage.
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Thus we achieve single-binary and the ability to fully localize ntldr and
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setupldr.bin for any locale.
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See boot\lib\i386\bootfont.h for the format of the bootfont.bin file.
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Note that Setup will install bootfont.bin. If this file becomes corrupt or the
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user deletes it, the ntldr will fall back to sbcs support via vga text mode.
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For this reason, it may be desirable to include English message resources
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(as well as the ones for the particular localization) in ntldr so at least
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the boot selection screens will be readable in English and not just display
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as garbage.
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Still to do some day, issues, problems, etc:
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- If non-x86 machines' firmware starts to support DBCS we should be able to
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extend support to these machines orthoganally since the x86 implementation
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is entirely 'hidden' in the ARC emulation layer. The only thing we would need
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is a mechanism to 'trigger' dbcs mode, which is performed by the presence of
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bootfont.bin on x86 machines.
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- The ARC console is driven by control sequences that are introduced with 0x9b.
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Unfortunately this is a valid lead byte char in several Far East code pages.
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In Japan this doesn't bite us because we don't actually use any characters that
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lead with 0x9b. The fix is to replace use of 0x9b with ESC[ (escape-left bracket)
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which is a synonym. However we don't know if all ARC firmware out there
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supports that as a synonym, so #ifdef _X86_ would probably be necessary
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(that would be ok since we are not enabling dbcs for non-x86 machines anyway).
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- tedm, 7/11/95, Tokyo
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