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This size was used to break up DMA transactions so that a single transaction would not cross a page boundary. This was because on Alpha, there was an actual page table which translated between PCI and DMA address spaces. On all currently implemented systems, the mapping is simply to add a scalar offset, so it's not possible for a legal region of memory to be contiguous in one space but not in the other. Additionally, if it *was* possible for there to be a mismatch, it was only coincidence that Alpha used a page table which had the same sized pages as it normally used. There is no requirement that there even would be fixed sized pages in the first place. To avoid this artificial dependency between the IDE controller and the ISA, this change simply changes the chunk size for DMA accesses to 4K. That's the page size at least on x86 and probably other architectures, and will be a pretty close approximation of the previous behavior. It's possible that even having this chunking in the first place is unnecessary and functionally useless, but there are some checks which happen between chunks, and changing how big they are would change the frequency of those checks. For instance, the controller/disk may not notice in the same amount of time if a DMA was cancelled somehow. Change-Id: I1ec840d1f158c3faa31ba0184458b69bf654c252 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34178 Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Maintainer: Gabe Black <gabeblack@google.com> Tested-by: kokoro <noreply+kokoro@google.com>
This is the gem5 simulator. The main website can be found at http://www.gem5.org A good starting point is http://www.gem5.org/about, and for more information about building the simulator and getting started please see http://www.gem5.org/documentation and http://www.gem5.org/documentation/learning_gem5/introduction. To build gem5, you will need the following software: g++ or clang, Python (gem5 links in the Python interpreter), SCons, SWIG, zlib, m4, and lastly protobuf if you want trace capture and playback support. Please see http://www.gem5.org/documentation/general_docs/building for more details concerning the minimum versions of the aforementioned tools. Once you have all dependencies resolved, type 'scons build/<ARCH>/gem5.opt' where ARCH is one of ARM, NULL, MIPS, POWER, SPARC, or X86. This will build an optimized version of the gem5 binary (gem5.opt) for the the specified architecture. See http://www.gem5.org/documentation/general_docs/building for more details and options. The basic source release includes these subdirectories: - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - src: source code of the gem5 simulator - system: source for some optional system software for simulated systems - tests: regression tests - util: useful utility programs and files To run full-system simulations, you will need compiled system firmware (console and PALcode for Alpha), kernel binaries and one or more disk images. If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.