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Most CF Cards Fail DMA Transfers
Anomalyst writes "In his quest to create an open source video camera, Andrey Filippov of elphel.com has determined that most Compact Flash devices, although claiming to be DMA capable, do not perform Direct Memory Access transfers correctly. This means successful movement of data to and from the device takes much more time with DMA disabled." The culprit appears to be the controller chip packaged with most of the CF cards Filippov tried. We last visited Elphel and their work on open source digital cameras in 2002. Filippov gave a Tech Talk at Google last year.
It wasn't that long ago that I read here how the DMA capability of FireWire devices is a gaping security hole. Shouldn't we feel safer that most compact flash devices don't have the same problem?
Reminds me of the infamous Soundblaster crackle... Which in this thread is being discussed around X-Fi hardware. Even though I can remember the very first Live!'s giving me and my friends the problem years ago. I don't recall the exact details of the situation but I believe it was an improper PCI implementation.
On the Oregon Cost born and raised, On the beach is where I spent most of my days
I haven't seen a digital camera that requires separate drivers in ages. My own camera is detected as a USB hard drive - XP, Vista, and Ubuntu alike - and it's more than four years old.
It would not be possible to get the performance the camera gets if it did not use DMA mode. It may be that it uses 1K blocks like the article says they used for a workaround. The cards also work fine in UDMA capable external readers, otherwise I would be seeing a ton of messages in the camera forums I frequent. Sandisk and Lexar UDMA CF cards are frequently used with the new cameras that can support it and are widely used by professional photographers.
Also, the article said that the Sandisk card they tried worked. They did not mention anything about Lexar but did mention problems with Transcend, which is not certified for my camera.
This post is encrypted twice with ROT-13. Documenting or attempting to crack this encryption is illegal.
A while ago I built my mythtv frontend, (based off a T-Online vision s100 box) and elected to use a CF card for storage within the unit - the box is entirely free of moving parts, so CF made sense.
I bought one of those IDE to CF adapters off ebay, and found that when I turned on DMA, the IDE bus would basically lock up, and pretty much end up useless.
After a lot of fiddling and digging around, I discovered that the adapter did not connect the required pins for DMA transfers to work. Old-skool CF never had DMA, so this extra pin is only a recent addition to the standard.
Anyway, I soldered in a short wire to hook up this pin, and now I get respectable dma transfers.
The moral of the story - it might not be the CF card that is causing DMA failure, but the adapter it's hooked into.
Sparks:Gadget:Beer Maker