It seems there's an errata with the XScale core that causes self-modifying code (including linkers and loaders) not to work if write coalescing is disabled in CP15. Check to make sure that it is enabled in register 0.
Also, make sure that the cache flush you are calling invalidates the I-cache after flushing the D-cache.
One other thing to try to make sure that it's a cache issue (what it sounds like), is to try running it with caches disabled on startup.
If you need any more help, feel free to contact me!
Mike
Devon H. O'Dell wrote:
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
