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Observer jahogan
Observer
10,087 Views
Registered: ‎11-06-2012

Virtex-6 LX75T readback fault

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Hello,

I am working on implementing readback on a Virtex-6 device ( xc6vlx75tff484-1 ) via a SelectMAP x8 interface using an external microprocessor.  The design I am reading back is a system with 9 reconfigurable partitions each containing a Microblaze.  At some point during the readback process the Microblazes halt.  This occurs before the FAR is incremented into the BRAMs.  Can anybody hypothesize why readback of type 000 resources might cause a design to fault?  Does readback of distributed RAM cause the same problems as BRAM readback?  The readback data is verified against the original bitstream using the .msk file and everything checks out, the design just stops running at some point during the process.

Thanks,

J

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1 Solution

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Scholar austin
Scholar
14,889 Views
Registered: ‎02-27-2008

Re: Virtex-6 LX75T readback fault

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j,

 

A caution:  if you read back a BRAM contents frame, you might disturb the BRAM contents.

 

As long as you ONLY read configuration memory, then nothing will be disturbed.


LUTRAM/SRL have a bit set (GLUTMASK) that causes the contents of LUTRAM and SRL to be unaffected by a read, or a write (when you reasd, you get zeros).

 

If you have any DRP blocks (dynamic reconfigurable programming), then watch out.  For example, a DRP bit is made accessible to the fabric (for the DCM as an example, or MMCM).  Then if the control for this DRP gets stepped on, it may end up changing one or more of those DRP bits.

 

 

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Scholar austin
Scholar
10,079 Views
Registered: ‎02-27-2008

Re: Virtex-6 LX75T readback fault

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j,

 

How did you create the reconfigurabe bitstreams?

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Observer jahogan
Observer
10,076 Views
Registered: ‎11-06-2012

Re: Virtex-6 LX75T readback fault

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Austin,

I created the bitstreams by calling bitgen from the PlanAhead tool with the following options:

 

 -l -m -bd *.elf -g Persist:Yes -g ActiveReconfig:Yes -g EssentialBits:Yes -g Readback

 

J

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Scholar austin
Scholar
10,063 Views
Registered: ‎02-27-2008

Re: Virtex-6 LX75T readback fault

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which version?

Austin Lesea
Principal Engineer
Xilinx San Jose
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Observer jahogan
Observer
10,058 Views
Registered: ‎11-06-2012

Re: Virtex-6 LX75T readback fault

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I'm running 13.4 right now.  I tried upgrading to 14.4, but I ran into the problem of the optional CSO_B pin being persisted and unavailable for use as GPIO after configuration.

If interested, this post has more details on that problem:

http://forums.xilinx.com/t5/Design-Planning/Error-Bitgen-145-Optional-CSO-B-configuration-pin-persisted/m-p/282784

 

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Scholar austin
Scholar
10,052 Views
Registered: ‎02-27-2008

Re: Virtex-6 LX75T readback fault

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j,

 

My thought is that your are interrupting something, you just don't know what.


I would cut the problem down, sort of divide an conquer to identify exactly which bitstream fragment is causing the problem.

 

I know of nothing that would case the problem, other than you are stepping on something that is working, and changing its configuration.

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Observer jahogan
Observer
10,047 Views
Registered: ‎11-06-2012

Re: Virtex-6 LX75T readback fault

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Thanks Austin,

I'm currently formulating a plan for determining the FAR value exactly when the system halts during readback and using the *.ll file to at least identify the responsible net.  I've got a program that allows me to do a word-by-word readback of configuration data and the FAR value, I just need to figure out how to determine when the fault has occurred and feed it back into the readback controller.

 

J

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Scholar austin
Scholar
14,890 Views
Registered: ‎02-27-2008

Re: Virtex-6 LX75T readback fault

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j,

 

A caution:  if you read back a BRAM contents frame, you might disturb the BRAM contents.

 

As long as you ONLY read configuration memory, then nothing will be disturbed.


LUTRAM/SRL have a bit set (GLUTMASK) that causes the contents of LUTRAM and SRL to be unaffected by a read, or a write (when you reasd, you get zeros).

 

If you have any DRP blocks (dynamic reconfigurable programming), then watch out.  For example, a DRP bit is made accessible to the fabric (for the DCM as an example, or MMCM).  Then if the control for this DRP gets stepped on, it may end up changing one or more of those DRP bits.

 

 

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Observer jahogan
Observer
10,011 Views
Registered: ‎11-06-2012

Re: Virtex-6 LX75T readback fault

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Thanks for that last post.  Clearing the GLUTMASK bit in the CTL0 register prevented the fault from happening during readback.  It would have taken me awhile to solve that problem. 

 

For anyone else who may run into a similar problem, the bitgen flag to clear the GLUTMASK bit to 0 was:

 

-g GLUTMASK_B:0

 

In the Virtex-6 Configuration User Guide the syntax is -g Glutmask:Yes/No, which didn't work for the V6.  In that document it says it's only supported in Spartan-3A and 6 devices. 

 

Thanks again Austin, big help!

J

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