More about the NitrOS-9 Boot file

The NitrOS-9 Boot file is used during the second stage of the boot process. It contains the additional modules required to bring the system to a running state. See also The NitrOS-9 Boot Process Explained, More about the NitrOS-9 Kernel file and More about SysGo.

The Boot file is created by concatenating multiple binary modules.

This works because each NitrOS-9 module is relocatable code and because there is a header on each module which allows the modules to be treated as a linked list that is searchable by module name.

How to create a Boot file

There are two ways to create a Boot file:

• If you create a boot file during the NitrOS-9 build process, the contents of the Boot file is specified in a makefile -- typically, the makefile for a particular target will define multiple Boot file variants and create disk images for some or all of them.
• If you create a boot file on a running NitrOS-9 system, a utility called os9gen can be used to create a new Boot file and to update the pointer in LSN0. The contents of the Boot file are typically defined by a file in the NITROS9/<target>/BOOTLISTS directory. After running os9gen on a disk, rebooting the system using that disk will use the new Boot file.

Boot file examples for Level 1

The Boot files for Coco1 Level 1 are defined in level1/coco1/bootfiles/makefile

Here is the definition of a sample Boot file for Coco1 Level 1 from that file:

  BOOTFILE_COVDG  = $(MD)/ioman \
                    $(MD)/rbf.mn \
                    $(FLOPPY_40D) \
                    $(MD)/ddd0_40d.dd \
                    $(MD)/scf.mn \
                    $(VTIO_COVDG) \
                    $(MD)/scbbp.dr $(MD)/p_scbbp.dd \
                    $(MD)/scbbt.dr $(MD)/t1_scbbt.dd \
                    $(PIPE) \
                    $(CLOCK60HZ) \
                    $(MD)/sysgo_dd
   
  VTIO_COVDG      = $(MD)/vtio.dr $(MD)/covdg.io $(MD)/term_vdg.dt

The VTIO stuff is code to control text output on the memory-mapped/character mapped display, including code to do scroll under software control.

Here is an example of a minimal Boot file, from level1/mc09/bootfiles/makefile

  BOOTFILE_MC09SD = $(MD)/ioman \
                    $(MD)/rbf.mn \
                    $(MD)/dds0_80d.dd \
                    $(MC09SDC_80D) \
                    $(MD)/scf.mn \
                    $(TERM_MC09) \
                    $(PIPE) \
                    $(CLOCK50HZMC09) \
                    $(MD)/sysgo_dd
  
  TERM_MC09       = $(MD)/mc6850.dr $(MD)/term_mc6850.dt $(MD)/term_mc6850_t0.dt $(MD)/term_mc6850_t1.dt
  MC09SDC_80D     = $(MD)/mc09sdc.dr $(MD)/s0_80d.dd $(MD)/s1_80d.dd $(MD)/s2_80d.dd $(MD)/s3_80d.dd

The MC09 only supports VT100-style terminal I/O through physical and virtual UARTs, and so the VTIO modules are not needed; instead, modules drivers for serial I/O are present.

Boot file examples for Level 2

The Boot files for Coco3 Level 2 are defined in level2/coco3/bootfiles/makefile

Here is the definition of a sample Boot file for Coco3 Level 2 from that file:

  BOOTFILE_80D    = $(MD)/krnp2 $(MD)/ioman $(MD)/init \
                    $(MD)/rbf.mn \
                    $(FLOPPY_80D) \
                    $(MD)/ddd0_80d.dd \
                    $(MD)/scf.mn \
                    $(VTIO_COGRF_80) \
                    $(PIPE) \
                    $(CLOCK60HZ)
  
  VTIO_COGRF_80   = $(MD)/vtio.dr \
                    $(MD)/keydrv_cc3.sb $(MD)/joydrv_joy.sb $(MD)/snddrv_cc3.sb \
                    $(MD)/cogrf.io \
                    $(MD)/term_win80.dt \
                    $(MD)/w.dw $(MD)/w1.dw $(MD)/w2.dw $(MD)/w3.dw $(MD)/w4.dw \
                    $(MD)/w5.dw $(MD)/w6.dw $(MD)/w7.dw

The VTIO stuff is code to control windowed text output on the memory-mapped/character mapped display.

Here is an example of a minimal Boot file, from level2/mc09l2/bootfiles/makefile

  BOOTFILE_MC09SD =  $(MD)/krnp2 $(MD)/ioman $(MD)/init \
                     $(MD)/rbf.mn \
                     $(MD)/dds0_80d.dd \
                     $(MC09SDC_80D) \
                     $(MD)/scf.mn \
                     $(TERM_MC09) \
                     $(PIPE) \
                     $(CLOCK50HZMC09)
  
  TERM_MC09       =  $(MD)/mc6850.dr $(MD)/term_mc6850.dt $(MD)/term_mc6850_t0.dt $(MD)/term_mc6850_t1.dt
  MC09SDC_80D     =  $(MD)/mc09sdc.dr $(MD)/s0_80d.dd $(MD)/s1_80d.dd $(MD)/s2_80d.dd $(MD)/s3_80d.dd

Bootlist examples

Here are some example bootlist files:

• level1/coco1/bootlists/standard.bl
• level1/mc09/bootlists/standard.bl
• level2/coco3/bootlists/standard.bl
• level2/mc09l2/bootlists/standard.bl

What to include in a Boot file

A Boot file stays in memory for the life of the session; there is no way to unstitch parts of it. For Level 1, the restricted amount of memory available (maximum of 64Kbytes) means that the Boot file should only contain what's necessary to boot the system. For Level 2, the additional memory made available by the DAT means that you may not need to be so determined to restrict what's present.

When you load modules one-at-a-time each module is aligned to a page (256-byte) boundary and some memory is wasted. When you concatenate multiple modules (as in, for example, the Boot file) the individual modules (apart from the first one) are not necessarily aligned in memory - which means that they are stored more efficiently.

A "hybrid" approach is to create a minimal Boot file and then concatenate groups of modules to be loaded-on-demand at a later time. For example, if you do not require DriveWire to boot your system:

• Omit DriveWire modules from your Boot file
• Append the necessary DriveWire drivers and descriptors into a file
• Load that file after boot, when needed, and unload it when not needed.

The commands would look like this:

   merge driver descriptor1 [descriptor2..]>somename
   attr somename e pe
   load somename
   ..
   ..
   unlink somename

You should only 'unlink' modules that have been placed in memory by use of 'load'.

SysGo or not SysGo?

A Level 1 Boot file must include the SysGo module. For a Level 2 Boot file, the SysGo module is optional. In the Level 2 examples above, the Boot file does not include the SysGo module. See More about SysGo.