README.altboot revision 1.2 
1/// notes about altboot ///
2
3$NetBSD: README.altboot,v 1.2 2011/03/13 15:23:43 phx Exp $
4
5Altboot is a functional bridge to fill the gap between a NAS product
6custom bootloader and the NetBSD kernel startup environment.  Altboot
7irons out and rectifies erroneously configured HW by product
8bootloaders and prepares a sane runtime better suited for booting
9NetBSD kernels.
10
11- provides the foundation of a fast NetBSD porting cycle with functionalities
12  product bootloaders don't have.
13- facilitates a flexible and clean NetBSD implementation tailoured
14  to target HW in detail, minimizing bumpy adjustments and hacks in
15  locore asm and machdeps in very early kernel startup stage.
16- levels out differences among similar-but-not-the-same porting
17  targets to make it possible having common NetBSD kernels for them.
18- builds and hands a bootinfo list to the NetBSD kernel.
19
20Altboot is known working on at least three models.
21- KuroBox with a popular U-Boot as the replacement of vendor proprietary
22
23   U-Boot 1.1.4 LiSt 2.1.0 (Sep 21 2006 - 00:22:56) LinkStation / KuroBox
24
25- Synology 101g+ with vendor custom PPCboot
26
27   PPCBoot 2.0.0 (Mar  1 2005 - 15:31:41)
28
29- D-Link DSM-G600 with heavily restricted vendor custom U-Boot
30
31   U-Boot 0.2.0 (May 26 2005 - 19:38:32)
32
33The standard use of altboot is to invoke it with a short script from
34U-Boot/PPCboot, where the altboot image is stored in an unoccupied 128KB
35section of the target's HW NOR flash.  Combined with standard
36U-Boot/PPCboot functions, it is possible to boot a NetBSD kernel off
37it right after power-on, without the help of manual intervention.  Note
38that the original U-Boot/PPCboot still remains useful and altboot works
39as a functional extension for them.
40
41Altboot hands the following bootinfo records to the NetBSD/sandpoint
42kernel.
43- processor clock tick value driving MPC8241/8245.
44- serial console selection.
45- booted kernel filename and which device it was fetched from.
46- Ethernet MAC address, if target HW lacks SEEPROM to store a unit unique
47  value.
48- product family indication.
49- preloaded kernel module names (under development).
50
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