Opened 8 years ago

Closed 7 years ago

#1411 closed enhancement (wontfix)

Video compression buffers may be needed.

Reported by: jg Owned by: rsmith
Priority: high Milestone: Trial-3
Component: distro Version:
Keywords: power Cc: JordanCrouse, jg
Blocked By: Blocking:
Deployments affected: Action Needed:
Verified: no

Description (last modified by jg)

The Geode has video compression buffers that can greatly reduce the memory bandwidth required to drive the display, but since we haven't seen any problems with bandwidth starvation on the mbus yet,it might be a non starter.

Leaving it off saves us oodles of video space, and we just recently discovered that EXA doesn't like having its stride pulled out from underneath it, meaning that we would probably have to have the compression pitch enabled for the non-visible space too, which would be a total waste.

On the other hand, memory references to the RAM chips take power, so the compression buffers may be needed to reduce power consumption when driving the display. But the idle display may be able to be handled by the DCON, (if we can tolerate the latency effects, which are not great if the video drivers are left on in the Geode), so this is not an obvious decision at all.

The compression buffers have been working in the past; but we need to make real measurements to decide the cost/benefit ratio of using them.

It is something we need to investigate carefully as part of the power management work.

Change History (4)

comment:1 Changed 8 years ago by jg

  • Cc jg added
  • Keywords power added
  • Milestone changed from CTest to BTest-4

comment:2 Changed 8 years ago by jg

  • Description modified (diff)

comment:3 Changed 7 years ago by jg

  • Milestone changed from BTest-4 to Trial-2
  • Verified unset

Since latency from DCON is lower than previously believed, we think that compression buffers probably won't be needed. Keeping open until ajax's work completes and proves this belief.

comment:4 Changed 7 years ago by jg

  • Milestone changed from Trial-2 to Trial-3
  • Resolution set to wontfix
  • Status changed from new to closed

Not planning to do; are working on #1412 as a better alternate.

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