You've described a relatively complicated procedure well in this document.
My only suggestion would be to reference the applicable source code files
throughout the text, so that it's easy to find the associated code.
Richard Schilling
Webmaster / Web Integration Programmer
Affiliated Health Services
Mount Vernon, WA USA
http://www.affiliatedhealth.org
phone: 360.856.7129
> -Original Message-
> From: Alan Cox [mailto:[EMAIL PROTECTED]]
> Sent: Friday, June 22, 2001 9:21 AM
> To: [EMAIL PROTECTED]
> Subject: For comment: draft BIOS use document for the kernel
>
>
>
> Linux 2.4 BIOS usage reference
>
>
> Boot Sequence
> -
>
> Linux is normally loaded either directly as a bootable floppy
> image or from
> hard disk via a boot loader called lilo. The kernel image is
> transferred
> into low memory and a parameter block above it.
>
> When booting from floppy disk the BIOS disk parameter tables
> are replaced
> by a new table set up to allow a maximum sector count of 36
> (the track size
> for a 2.88Mb ED floppy)
>
> int 0x13, AH=0x02 is issued to to probe and find the disk geometry.
> int 0x13, AH=0x00 is used to reset the floppy controller.
> int 0x13, AH=0x02 is then issued repeatedly to load tracks of
> data. The
> boot loader ensures no issued requests cross the track
> boundaries
>
>
> int 0x10 service 3 is used during the boot loading sequence
> to obtain the
> cursor position. int 0x10 service 13 is used to display
> loading messages
> as the loading procedure continues. int 0x10 AH=0xE is used
> to display a
> progress bar of '=' characters during the bootstrap
>
>
> Control is then transferred to the loaded image whether by
> the floppy boot
> loader or other services
>
>
> Kernel Setup
>
>
> The initial kernel setup executes in 16bit mode. While in
> 16bit mode the
> kernel calls and caches data from several 16bit calls whose
> data is not
> available in 32bit mode
>
> It then uses int 0x10 AH=0x0E in order to print initial
> progress banners so
> that immediate feedback on the boot status is available. The
> 0x07 character
> is issued as well as printable characters and is expected to
> generate a
> bell.
>
> Memory detection is done as follows, attempting to handle the various
> methods that have been available over time
>
> Memory Sizing
> -
>
> Firstly a call is made to BIOS INT 15 AX=0xE820 in order to read the
> E820 map. A maximum of 32 blocks are supported by current kernels. The
> 'SMAP' signature is required and tested. In addition the SMAP
> signature
> is restored each call, although not required by the
> specification in order
> to handle some know BIOS bugs.
>
> If the E820 call fails then the INT 15 AX=0xE801 service is
> called and the
> results are sanity checked. In particular the code zeroes the
> CX/DX return
> values in order to detect BIOS implementations that do not set them
> usable memory data. It also handles older BIOSes that return
> AX/BX but not
> AX/BX data.
>
> When service E801 is used the kernel assumes that usable
> memory extends from
> 4K to the bottom of the EBDA, and from 1Mbyte to the top of
> the E801 area.
>
> If neither service is available then INT 0x15 AH=0x88 is
> invoked in order to
> get the memory size, up to 64Mb by the original IBM PC BIOS service.
>
> Peripherals
> ---
>
> Having sized memory the kernel moves on to set up
> peripherals. The BIOS
> INT 0x16, AH=0x03 service is invoked in order to set the
> keyboard repeat
> rate and the video BIOS is the called to set up video modes.
>
> The kernel tries to identify the video in terms of its
> generic features.
> Initially it invokes INT 0x10 AH=0x12 to test for the
> presence of EGA/VGA
> as oppose to CGA/MGA/HGA hardware.
>
> INT 0x10 AH=0x03 is used to obtain the cursor position, and INT 0x10,
> AH=0x0F is used to obtain the video page and the mode. If EGA or VGA
> are present the normal BIOS locations of 0x485 and 0x484 are
> used to obtain
> the font size and the screen height.
>
> VESA BIOS video services are used to obtain the amount of
> video memory
> (INT 0x10 AX=0x4F00) and then to obtain the VESA 2.0
> protected mode interface
> data if available (INT 0x10, AX=0x4F0A). Users are able to
> select graphical
> video modes (INT 0x10 AX=0x4F02), or if not available the pre
> VESA mode
> setup. The presence of the VESA BIOS is checked by the VESA get mode
> information call (INT 0x10 AX=0x4F01)
>
> Special modes will also invoke INT 0x10 AH=0x1200 (Alternate
> print screen),
> INT 0x10 AH=0x11 (to set 8x8 font), INT 0x10 AH=0x1201 (to
> turn off cursor
> emulation) and INT 0x10 AH=0x01 (to set up the cursor).
>
> Having completed video set up the hard disk data for hda and
> hdb is copied
> from the low memory BIOS area into the kernel tables. INT
> 0x13 AH-0x15 is
> used to check if a second disk is present.
>
> INT 0x15, AH=0xC0 is invoked in order to check f
