Mailing Lists: Apple Mailing Lists
Image of Mac OS face in stamp
 
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Zero-copy PXI-X driver for G5 Mac, process access to 7 GB memory

Drew,
While I can not comment on when/if the AppleMacRiscPCI driver will/would be released into open source, I can comment a bit about how the DART works. Really we don't want developers to worry about the specifics of how the DART works, because it can change. The IOMapper is the interface that we are supporting.
The DART translates all memory accesses from HyperTransport/PCI devices in the range of 0 to 2 GB to a 36 bit physical memory address. The translations are managed by page. The driver for the DART manages the 2 GB space with a power of 2 allocator. This allows most allocations/mappings the be handle in a single contiguous extent. If a client requests a disk read on 1 MB of its memory, those pages could be anywhere in physical memory. The Mapper will use the DART to create a single 1 MB extent that a PCI device can use for DMA. Even though the memory is not really contiguous, the driver for the PCI device will usually be able to treat it as if it is contiguous.
The DART is only able to map 2GB of memory for active DMA. It is not possible to give a HT/PCI device access to more than 2 GB of memory at a given time.
If you can, please describe the environment you are working in. There may be ways around the limitations of the current system.

Josh


At 9:46 AM -0500 11/13/03, Andrew Gallatin wrote:
Josh de Cesare writes:
> Later the client will make a request that will start DMA to
> one of the memory chunks. The driver will look up the chunk in the
> control structures. It will then use one or more of the DMA windows
> and set their mappings with IOMapperInsertPPNPages and the previously
> collected physical page list. Then the driver can initiate the DMA
> activity. Obviously, the windows and mappings can not be reused

So this method is zero-copy, but not OS-bypass.. It may be helpful
for the original author, but its useless for me.

Does Apple plan to ever open source com.apple.driver.AppleMacRiscPCI
so we can see how the Dart actually works?

Drew
_______________________________________________
darwin-drivers mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/darwin-drivers
Do not post admin requests to the list. They will be ignored.


Visit the Apple Store online or at retail locations.
1-800-MY-APPLE

Contact Apple | Terms of Use | Privacy Policy

Copyright © 2007 Apple Inc. All rights reserved.