waynekford
1 Copper

T1600 PCIe introduces random latency during DMA

We are trying to complete the development of a high speed image capture card.  It is a PCIe card that is channeled into a Dell Precision T1600 workstation via a DataPath PCIe bus extender.  Data is dma'd into the Dell.  During testing, we found that a rare and irregular spaced latency occurs, for up to 1 ms, during the DMA.  The card is to handle large (100GB-1TB sized) image files, and this latency corrupts the resultant "image".  We were targeting a T1700 platform for the product until this issue arose.  We tested the same hardware using an ASUS motherboard and detected no errors over a 24 period.  We've excluded processor loading, etc.

Is this bug possibly already known?  Is there a work around?

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7 Replies
RoHe
6 Indium

RE: T1600 PCIe introduces random latency during DMA

Do you have the latest version of BIOS, A16, on the T1600?

Fixes & Enhancements

1. Addressed system intermittently does not respond to keyboard.
2. Addressed UEFI OS fail boot with HDD password present issue.
3. Addressed CCTK issues.
4. Improve the compatibility of PCI devices and USB devices.
5. Update Intel Microcode for SandyBridge processor.
6. Update Intel PXE ROM.

Ron

   Forum Member since 2004
   I am not a Dell employee

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waynekford
1 Copper

RE: T1600 PCIe introduces random latency during DMA

Oh, yes.  Firmware and bios checks were the first things we looked at, once we realized the issue is not our add-in card but something else on the Dell.

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RoHe
6 Indium

RE: T1600 PCIe introduces random latency during DMA

Do you have the latest Intel chipset and ME drivers too?

Could this have something to do with the speed and/or latency of the RAM in the T1600?

Ron

   Forum Member since 2004
   I am not a Dell employee

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Highlighted
waynekford
1 Copper

RE: T1600 PCIe introduces random latency during DMA

We walked through the entire list posted at Dell to be sure the software/firmware was up to date.  There are no reported problems with RAM during these tests.  The DMA transactions are randomly stalled for a millisecond (or less, variable, we've measured this).  It seems to be purely a bus transaction issue.  As you suspect, we doubt that Dell is fully complying with the PCIe spec for x16 transfers.

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RoHe
6 Indium

RE: T1600 PCIe introduces random latency during DMA

I guess only Dell can answer the question about compliance with the PCI-e specs...

Only other thing I could suggest is trying your board on a different T1600 to see if this problem is "universal" or just something specific to the unit you've been using for your testing...

Ron

   Forum Member since 2004
   I am not a Dell employee

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waynekford
1 Copper

RE: T1600 PCIe introduces random latency during DMA

Thanks for your interest.  I tried penetrating Dell to find out something about compliance.  They vectored me to this board.

What I'm trying to avoid is to plan on the T1700 series workstation for our product.  I don't  have a properly configured T1600 here (our test system is in the UK where the software engineer is), but they appear to have identical PCIe specs in the public documentation.  What particularly bothers me is that our hardware doesn't have a problem with the ASUS motherboard.  (Dell's appeal to us is in part, that they are worldwide.  So we are hesitant to change to a smaller system vendor.)

I'm looking here for somebody who has had issues with the PCIe on the 1600 MB and whether they could explain our problems.

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RoHe
6 Indium

RE: T1600 PCIe introduces random latency during DMA

This a user-to-user forum, so unless there's some user out there with a T1600 who's experienced the same issue, I don't know if anyone here will be able to help.

Since you said this is a random, millisec issue, others may never notice a problem if their needs are less demanding than yours.

And for all anyone knows, the T1600 could be tight on PCI-e specs but the Asus is "sloppy" and more tolerant of faults, possibly even in your own hardware...?

Ron

   Forum Member since 2004
   I am not a Dell employee

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