Some hints on porting d-i to a new architecture.

This will try to document the places you need to modify d-i to support your
new architecture, but it's necessarily incomplete, not coering topics like
getting a working kernel for your architecture, or making install images
that have the necessary magic to be bootable on your architecture.

It assumes that you're working from a subversion checkout of the d-i tree,
and will be building packages from it and uploading them to your archive.

If you're not already well familiar with Debian development, d-i, and the
specifics of your architecture, this document is not likely to be useful to
you.

* archive

  First, you're going to need an archive for packages for your
  architecture. It will need to be similar to the official Debian mirrors
  for d-i to work.
  
  In particular, d-i needs the dists/suite/Release file, the
  dists/suite/main/binary-yourarch/Release file, and
  dists/suite/debian-installer/binary-yourarch/Packages.gz, as well as all
  the debs and udebs etc.

  A partial test of your archive is to see if debootstrap can sucessfully
  use it.

* gpg key

  If you're using a gpg key to sign your archive, you will need to update
  the debian-archive-keyring package to include your key, and install the
  package before building your installer images, so the installer includes
  your key.

  If you're not using a gpg key, you will need to preseed
  debian-installer/allow_unauthenticated=true.

* Architecture fields

  Many d-i udebs have Architecture fields that limit the udeb to a subset
  of architectures. For example, packages/netcfg/debian/control lists most
  arches (except for s390). Others include clock-setup, and kbd-chooser.
  You will need to grep for all of these, and add your architecture to all
  of them that it makes sense to add it to.

* libdebian-installer

  In packages/libdebian-installer/src/system there are files that are used
  to determine the aubarch of a system. By default the subarch is
  "generic"; if your architecture has subarches you may need to add a new
  file for your architecture, and edit the Makefile to include it.

* partman

  packages/partman/partman-partitioning/lib/disk-label.sh has a
  default_disk_label function that you will need to extend so it knows what
  kind of disk label is the default on your architecture.

* kernel udebs

  Unless you're using monolithic kernels, you will need to create kernel
  module udebs. The simplest way is to go into packages/kernel/ and copy
  and modifiy of the linux-kernel-di-* directories.

  This web page may also be helpful:
  http://wiki.debian.org/DebianInstaller/Modify/CustomKernel

* base-installer

  packages/base-installer/kernel/ contains files for each architecture that
  select a kernel package to install. Copy and modify one of the files for
  your architecture. You can also copy and modify stuff in the tests/
  subdirectory to use the regression test suite to make sure your file
  works.

* kbd-chooser

  packages/kbd-chooser/Makefile contains some architecture tests that set
  options based on what kinds of keyboards an architecture has. Add your
  architecture.

* building images

  installer/build/config/ contains files for each architecture that define
  the images to build, the kernel version to use, etc. You'll need to add
  one for your architecture, as well as a installer/build/config/yourarch/
  subdirectory with the rest of the .cfg files needed to build the images.

  installer/build/pkg-lists/ also contains per-architecture files, and
  you'll need to add files for your architecture there also.

  Once that's done, make all_build in installer/build should build some
  images. Good luck!
  
  (If it doesn't go as planned, the d-i team can assist with this most
  complicated stage in getting d-i working for your architecture.)

* lowmem

  packages/lowmem/debian-installer-startup.d/S15lowmem contains some
  architecture specific definitions of when the installer should enter low
  memory mode. It defaults to 64 megabytes for unknown architectures, which
  is higher than probably necessary for yours. The file contains some hints
  for getting more accurate numbers specific to your architecure.

* boot loader installer

  Finally, you'll probably need to add some way to make d-i install a boot
  loader for your architecture on the target system, using a boot loader
  installer. Existing boot loader installers live under packages/arch/, and
  if the boot loader is used for another architecture, you can modify one
  of these. If not, some programming will be needed..