[Coco] Re: NitrOS9 on MESS?

[Nathan Woods]

Roger Taylor writes: 

> At least you know that it's occuring while RBF is writing out to a
> storage device.  So if this does not happen on a real CoCo, and the code
> is  exactly the same, then it's M.E.S.S... probably a timing issue or the 
> index hole signal code.  ??

Truthfully, I do not know.  This particular bug defied almost all of my 
assumptions.  At first, I assumed that it was either a FDC timing bug or a 
6309 core bug.  However in my investigations, it seems that the orders to 
write to the bad sector come from outside cc3disk.  The fact that the bug 
occurs when used with a VHD - thus bypassing cc3disk - confirms this 
observation.  Since this bug also occurs with NitrOS-9 6809, the 6309 core 
is not to blame. 

Generally any bug that appears in MESS but not the real hardware is by 
definition, a MESS bug.  Probably the only bugs for which this is not the 
case is if some CoCo code was relying on something totally whacked out, such 
as reading from undefined IO memory or the contents of memory when power is 
turned on.  I'm inclined to believe that the latter is not the case.  It 
could be a timing bug, but what kind of timing bug would cause this bug.  As 
for "index hole signal code", can you elaborate on what that is?