xabi
Guest
Thu Feb 25, 2010 1:42 pm
Hi all,
Iam experimenting with Scrubbing in Xilinx Virtex-4 devices.
According to XAPP1088, pag.18:
"For scrubbing operations, there are special considerations for design
utilizing distributed RAMs and SRL16s. When a LUT is configured as eithe
SRL16 or distributed RAM (LUT RAM), scrubbing can corrupt the contents o
such primitives if GLUTMASK_B bit is left at its default setting o
‘1’. Therefore, it is important to ensure the GLUTMASK_B bit is set t
‘0’. Block RAM content, however, is not covered by the GLUTMASK_
setting. Therefore, block RAM content configuration columns still need t
be 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 colum
have been used as SRL16, initialized to a given value. I have checked i
this bitstream that the computed ECC codes (in the 21st word of th
configuration frame for this CLB column) were equal to 0x000!! As expected
this confirms that LUTs configured as SRL16s are not considered whe
computing the ECC.
2) I have generated a bitstream in which some of the LUTs of a CLB colum
have been used as SRL16 and others as LUTs. In this situation the generate
bitstream incorporates ECC codes which are not equal to 0 in the 21st wor
of the configuration frame for this CLB column.
Consequently, I have confirmed that when computing the ECC codes for th
configuration frames, only those LUTs not configured as SRL16s or LUT-RAM
are taken into account. This creates me a question:
How can we know if a LUT is configured in one of these modes? I suppos
this information is encoded in the bitstream... Do anyone have any clu
about this?
I would really appreciate any information.
Thanks in advance.
Xabi
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he
Guest
Thu Feb 25, 2010 4:12 pm
Quote:
According to XAPP1088, pag.18:
"For scrubbing operations, there are special considerations for designs
utilizing distributed RAMs and SRL16s. When a LUT is configured as either
SRL16 or distributed RAM (LUT RAM), scrubbing can corrupt the contents of
such 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_B
setting. Therefore, block RAM content configuration columns still need to
be avoided during scrubbing."
I avoided these problems by not using SRLs and cutting BRAM contents out
of the partial bitfiles. This also makes reconfiguration faster, because
the bitfiles become significantly smaller.
Quote:
How can we know if a LUT is configured in one of these modes?
Do you need to? Have you tried reconfiguring your SRLs with the
GLUTMASK_B bit set accordingly?
-HE
