Hi all,

I am experimenting with Scrubbing in Xilinx Virtex-4 devices.

According to XAPP1088, pag.18:
"For scrubbing operations, there are special considerations for designsutilizing distributed RAMs and SRL16s. When a LUT is configured as eitherSRL16 or distributed RAM (LUT RAM), scrubbing can corrupt the contents ofsuch primitives if GLUTMASK_B bit is left at its default setting of‘1’. Therefore, it is important to ensure the GLUTMASK_B bit is set to‘0’. Block RAM content, however, is not covered by the GLUTMASK_Bsetting. Therefore, block RAM content configuration columns still need tobe avoided during scrubbing."

Based on this information, I have carried out two experiments:

1) I have generated a bitstream in which all the LUTs of a whole CLB columnhave been used as SRL16, initialized to a given value. I have checked inthis bitstream that the computed ECC codes (in the 21st word of theconfiguration frame for this CLB column) were equal to 0x000!! As expected,this confirms that LUTs configured as SRL16s are not considered whencomputing the ECC.

2) I have generated a bitstream in which some of the LUTs of a CLB columnhave been used as SRL16 and others as LUTs. In this situation the generatedbitstream incorporates ECC codes which are not equal to 0 in the 21st wordof the configuration frame for this CLB column.

Consequently, I have confirmed that when computing the ECC codes for theconfiguration frames, only those LUTs not configured as SRL16s or LUT-RAMsare taken into account. This creates me a question:

How can we know if a LUT is configured in one of these modes? I supposethis information is encoded in the bitstream... Do anyone have any clueabout this?
I would really appreciate any information.

Thanks in advance.

Xabi

	   
					
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