[Coco] NitrOS9 question

Sat Oct 7 17:34:56 EDT 2017

I looked back through my notes and I found:

bootfile failed for me when it was $3d0e bytes
when I expanded it by adding shell, it worked and was $5af0 bytes. I
experimented with including/excluding sysgo and found that this made no
difference

that's consistent with Dave's experience that the bootfile must be >$4401
bytes in size.

My theory is that it has nothing to do with the boot file itself or with
the order of modules in the bootfile but instead that it has to do with how
the first piece of memory is assigned after the (modules of the) bootfile
have run.

I spent several evenings with the emulator trying to trace through the
startup and figure out what was going on, without success. At the time I
had little understanding of the kernel data structures; I might fare better
if I tried again now having read Kevin Darling's book.

Also, at the time I assumed this was a bug associated with my port.

Dave's padding experiment suggests a debug approach to use in emulation:

* create 2 boot images: one with a too-small bootfile and the other with a
padded bootfile
* start each in turn and grab an instruction trace
* look at where the instruction traces differ
* from the trace differences, infer the cause.

Neal.

On 7 October 2017 at 22:10, Gene Heskett <gheskett at shentel.net> wrote:

> On Saturday 07 October 2017 16:10:50 Dave Philipsen wrote:
>
> > I don’t know much about vfy but would it notice and fix extra padding
> > in an OS9Boot file that did not belong to any of the modules therein?
> >
> It has an option to split the bootfile back into its component modules,
> and in the case of splitting a boottrack, (you must first run krnl2dir
> to convert track 34 into a true directory entry) it will save the 1st 6
> bytes in front of the first os9 module as a separate file, and anything
> beyond the crc of the last module will be saved out as a separate file.
> Work in an empty scratchable directory to make sure you don't have any
> false alarms as I don't recall the name I gave the 6 byte header.
>
> I never gave a consideration to this scenario, so I believe w/o the -s
> option it will just read from the end of the last module in os9 boot
> till eof without any action as its just marching fwd one byte at a time
> looking for the $87CD of the next module header. With only the -v
> option, it should not affect the existing os9boot file other than fixing
> any bad parities or crc's.  If you also give it a module name, it will
> only fix that module.  See the help screen it spits out when you do not
> give it any arguments. Adjusting a modules memory size is done by adding
> the hex value to the existing value, and throwing away the carry if
> there is one, which is a roundabout way to effect a reduction in a
> modules memory request. The result then is modulo $10000. Said a
> different way, changing the memory by a $10 byte reduction is done by
> adding $FFE0.
>
> Slightly clearer than the Missouri river used to be 83 years ago. :)
>
> > Dave
> >
> > > On Oct 7, 2017, at 8:55 AM, Gene Heskett <gheskett at shentel.net>
> wrote:
> > >> On Saturday 07 October 2017 07:27:45 Neal Crook wrote:
> > >>
> > >> That sounds completely reasonable. Memory is allocated based on the
> > >> module header declaration.. there's not really any way (or reason)
> > >> to look inside the module and determine whether its content is
> > >> valid/reasonable  (and no need for you to zero-out the unused
> > >> space). In fact you  probably need not change the size of the
> > >> bootfile blob at all.. just the header declaration for the last
> > >> module. Caveat: assuming you have crc checking turned off (as it is
> > >> by default)
> > >>
> > >> Neal
> > >
> > > Or you could use my vfy, which will fix the header parity and crc in
> > > one swell foop while adjustingthe size of the memory.  Its a swiss
> > > army knife about that stuff.
> > >
> > >>> On 7 Oct 2017 10:52, "Dave Philipsen" <dave at davebiz.com> wrote:
> > >>> Ok, I compiled a minimum headless OS9Boot file that should boot
> > >>> with a shell on T2 as my terminal.  The size of the bootfile is
> > >>> $42F8. When I try to boot with it, as expected,  it fails.  I get
> > >>> the banner text from Init and Sysgo.  Interestingly, sometimes
> > >>> when it boots I also get a string printed to the screen that says,
> > >>> "WHAT?"
> > >>>
> > >>> Now I use dEd and simply <D>iddle the file length to $4401 and
> > >>> manually clear out the extra data to all zeroes. Voila! NitrOS9
> > >>> boots and I get the shell prompt on my terminal!  If I diddle it
> > >>> one byte shorter to $4400 it will not boot.  So it apparently
> > >>> matters only that the length of the file is $4401 or longer.
> > >>>
> > >>> Another interesting point:  If I diddle the file length of OS9Boot
> > >>> even greater to $8000 it still boots but smap reports way less
> > >>> system memory. So that tells me that the system memory allocation
> > >>> is based upon the size of the OS9Boot file, not its actual
> > >>> contents. Apparently no check is made to the contents of the file
> > >>> or whether it contains 'non-modulized' data!
> > >>>
> > >>> Dave
> > >
> > > Actually in a normal system, system memory is used up by the number
> > > of devices each needing a $27 byte long table for each path
> > > descriptor. With 2 or more of each style in my boot files, I'm so
> > > low on sysram that I've not been able to actually format a floppy in
> > > a decade. All I can do is delete everything on it including the boot
> > > track if I want to make a new boot.
> > >
> > >>>> On 10/7/2017 2:48 AM, Neal Crook wrote:
> > >>>> My guess is that it will make no difference. If it does,
> > >>>> experiment 2 is to
> > >>>> pad with 0xff. I await the result with interest.
> > >>>>
> > >>>> Neal.
> > >>>>
> > >>>> On 7 Oct 2017 08:04, "Dave Philipsen" <dave at davebiz.com> wrote:
> > >>>>
> > >>>> That would be an interesting experiment. I’ll see if I can try
> > >>>> that this
> > >>>>
> > >>>>> weekend.
> > >>>>>
> > >>>>> Dave
> > >>>>>
> > >>>>> On Oct 6, 2017, at 11:12 PM, Barry Nelson
> > >>>>> <barry.nelson at amobiledevice.
> > >>>>>
> > >>>>> com> wrote:
> > >>>>>> What happens if you just pad the end of the OS9Boot file with
> > >>>>>> zeros?
> > >>>>>>
> > >>>>>> --
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> > >>>>>
> > >>>>> --
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> > > Cheers, Gene Heskett
> > > --
> > > "There are four boxes to be used in defense of liberty:
> > > soap, ballot, jury, and ammo. Please use in that order."
> > > -Ed Howdershelt (Author)
> > > Genes Web page <http://geneslinuxbox.net:6309/gene>
> > >
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>
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
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