[9fans] Small bits of progress on SIMpad, couple of ARM questions

["Devon H. O'Dell " <dodell@offmyserver.com>]

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Hey,

I'm hoping there's someone here who knows a bit more about ARM
than I do. I've grabbed the ARM specification and the docs on the
SA-1110 from Intel, and these are a real big help with learning
how the code works.

I've got the decompressor to inflate the kernel, but I'm having
trouble getting it to jump to the kernel afterwards. From what
I can tell is happening:

 o After compiling, the image I send looks like:
   +---------+  
	 | inflate | } 20KB, text of _start at 0xc0200010
	 +---------+  
	 |         | )
	 | kernel  | > ~420KB, text of _start at 0xc0008010
	 |         | )
	 +---------+

 o I generate a boot header and put it in flash, telling the
   loader to load this to 0xc0008000 and enter at 0xc0008010.

 o Since inflate is in front of the kernel, and it has the
   kernel magic, the bootloader sees that at 0xc0008010 and
	 jumps into it.

 o inflate knows it's at the wrong place, so it relocates
   itself to 0xc0200000 and jumps to the relocated address which
	 calls the main() in imain.c

 o this gunzips the kernel from 0xc0200000 + 20*1024 to
   0xc0008000.

 o Kernel's _start is at 0xc0008010 (I'm assuming the extra 16
   bytes are the a.out header for all these things?). This is
	 assigned to ``f''

 o cache is drained, (*f)() is called.

I've placed various debugging prints around, and it turns out
that I _cannot_ get the thing to jump there. Reading the docs on
the processor, there shouldn't be any differences between bitsy
and my SIMpad at this point. When the jump should occur, the
unit powers off after a short delay, and I have verified with
prints that it never actually reaches _start in 
/sys/src/9/bitsy/l.s

So I'm curious what's happening. Perhaps the MMU is turned on
somehow and I'm accessing an illegal offset, which causes a
memory fault to be generated, but since there's no handler, the
unit powers itself down? This is all I can think of at the
moment.

I've been reading the Linux source, and Walter Schweizer from
Siemens has been quite helpful at pointing me to to relevant
sections of Linux (which are surprisingly similar, when I'm able
to identify matching code). Are there any bitsy / ARM gurus who
might be able to give me some tips on what might be going wrong
at this early stage? If I can get past this, it should be 
comparatively trivial to get it running further :)

Kind regards,

Devon H. O'Dell

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