Maple freezing on PCI Target-Abort

[jfaslist]

Hi,
We have designed our own IBM970fx motherboard which is a  (almost)clone 
to the IBM Maple reference kit.
We are seeing that whenever a PIO read PCI cycle bound to the PCI bus 
that is across the AMD8111 is ended w/ a target-abort, the whole system 
freezes. The device signaling the TA is a PCI-VME bridge. It does so as 
the address passed is invalid.

When the system hangs, using the service processor, I can access some 
AMD8111, CPC925 registers from which I can draw the following conclusions:

1- The AMD8111 secondary status tells me the AMD8111 got a TA
2- The CPC925 status/command register (0cf8070010) tells me that the TA 
error was forwarded to the CPC925.
3- The CPC925 APIEXCP register tells me that a DERR exception was signaled.

 From what I can read on the CPC925 and IBM970 cpu user manual, the DERR 
is the bus error that is returned to the CPU by the CPC925 to let him 
know that the cycle ended w/ an error. I have the following questions:

-What exception vector is taking care of a DERR excp? From what I can 
see it seems to be the "machine check" vector. But that seems a bit 
drastic to me. After all this is just a PCI target abort.
-I expect that the normal behavior would be for the kernel to send a 
signal termination to the user process which caused the PIO READ PCI 
cycle (from a previously mmap()'ed VMA address). Is it  doable on this 
platform?  Since a READ operation is coupled by nature, I think this is 
the only acceptable way.

I have tried to set the MSR[RI] bit before doing the PCI cycle, but it 
didn't change change anything. Also on our design we disconnect the 
CPC925 checkstop pin from the 970 machine check pin.(see page 39 of 
cpc925 user's manual). So a DERR shouldn't cause a machine check I would 
think.

I realize that these questions are very H/W related but couldn't find 
the answer in IBM doc.

Thanks for the help,

-- 

Best regards,
_______________________________________
jean-francois simon - themis computer
5, rue irene joliot curie
38330 eybens - france
+33 (0)4 76 14 77 85

	

	
		
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