I've found a bug in NitrOS9 Level2, using the usual coco3 boot scheme ( {REL,BOOT,KRN} at $2600 and then loading OS9Boot) but doing it on my TFR9 single board computer. If you don't have enough modules in your OS9BOOT to get down to $A000, then a process can have its kernel Proc Structure allocated at or above $A000 (in my case, at $A100), and then when it makes OS9 system calls, the code that copies your registers back from the last few bytes of the proc structure (in my case in $A2Fx) maps your process's stack block in the $A000-$BFFF block -- and so you copy junk to the return registers, including the PC. The workaround is to add a few more modules to the OS9BOOT, so F$SRqMem cannot allocate $Axxx to a Proc structure. ( FYI, I'm using EMUDSK for /DD and SC6850 for /TERM. )

PROBLEM-Nov6