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README.altboot revision 1.3 
      1 /// notes about altboot ///
      2 
      3 $NetBSD: README.altboot,v 1.3 2011/04/08 08:29:07 phx Exp $
      4 
      5 Altboot is a functional bridge to fill the gap between a NAS product
      6 custom bootloader and the NetBSD kernel startup environment.  Altboot
      7 irons out and rectifies erroneously configured HW by product
      8 bootloaders and prepares a sane runtime, better suited for booting
      9 NetBSD 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 
     20 Altboot is known working on at least these models:
     21 
     22 - KuroBox or LinkStation with a popular U-Boot as the replacement of
     23   vendor proprietary
     24 
     25    U-Boot 1.1.4 LiSt 2.1.0 (Sep 21 2006 - 00:22:56) LinkStation / KuroBox
     26 
     27 - Synology 101g+ with vendor custom PPCboot
     28 
     29    PPCBoot 2.0.0 (Mar  1 2005 - 15:31:41)
     30 
     31 - D-Link DSM-G600 with heavily restricted vendor custom U-Boot
     32 
     33    U-Boot 0.2.0 (May 26 2005 - 19:38:32)
     34 
     35 - QNAP TS-101 (V200) with vendor custom U-Boot
     36 
     37    U-Boot 1.1.2 (Aug 28 2005 - 13:37:25) QNAP System, Inc.
     38 
     39 The standard use of altboot is to invoke it with a short script from
     40 U-Boot/PPCboot, where the altboot.bin image is stored in an unoccupied 128KB
     41 section of the target's HW NOR flash.  Combined with standard
     42 U-Boot/PPCboot functions, it is possible to boot a NetBSD kernel off
     43 it right after power-on, without the help of manual intervention.  Note
     44 that the original U-Boot/PPCboot still remains useful and altboot works
     45 as a functional extension for them.
     46 
     47 In case the firmware was crippled by the vendor so that it only boots
     48 Linux U-Boot images (D-Link), you can still use altboot by uploading
     49 altboot.img instead of the Linux kernel.
     50 
     51 Altboot hands the following bootinfo records to the NetBSD/sandpoint
     52 kernel.
     53 - processor clock tick value driving MPC8241/8245.
     54 - serial console selection.
     55 - booted kernel filename and which device it was fetched from.
     56 - Ethernet MAC address, if target HW lacks SEEPROM to store a unit unique
     57   value.
     58 - product family indication.
     59 - preloaded kernel module names (under development).
     60 
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