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Something to study

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joncampbell123 committed Feb 22, 2018
1 parent 19ca5c1 commit 34dfa9ccf06f80393030166f7fc45448532d2997
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* DosBox 0.74
I applied the patches that I developped for previous DosBox versions.
Then I tried to get more performance and it was hard. Currently, the normal
core seems to run 10 or 12 % faster that the original code.
The consuming part is the decoding of x86 instructions. I thought a small gain
will have a big effect but sometimes logical improvements caused regressions.
The archive contains the diff of the changes I made.
Please use the provided file "dosbox.conf" that works. Else, a default file
will be created but you will have to change the usescancodes value, setting it
to false instead of true (what leads to problems typing characters).
Thanks to David Braconnier for the icons !
Unsupported features :
- only use the normal core (that is the default one)
- launch editor and launch captures (that require execlp)
* How to use DosBox
The config file "dosbox.conf" is the place you will try some parameters
to make it running well on your Amiga.
If you want to avoid entering the mount command each time you run DosBox,
just have a look at the last lines of the file "dosbox.conf" and add the
commands you want to run at startup.
* What I changed in the sources
The core of the emulator is version hard to optimize and to read. It is very
difficult to change some things in that part due to the mess of the x86
instruction set and some stange coding rules (C++ code that is not always
object oriented, many macros and inline functions, ...). So I used the
wonderful tool Zoom (look at http://www.rotateright.com) on my MacMini running
Linux to find the other parts that could be optimized.
So the changes I applied are :
- src/cpu/core_normal.cpp : Activated C_CORE_INLINE, what increases the required
memory to compile, it only worked with 512 MB and the OS 4.1 paging system !
- include/paging.h : Used instructions to read half-words and words with
reversed bytes (PPC rulez !). Also changed a structure reorganizing TLB fields
in order to decrease the pressure on the cache.
- include/paging.h (again !) : Tried to improve the memory access through TLB.
- src/cpu/modrm.cpp and other files : I reduced the size of arrays to decrease
the pressure on the cache.
- include/render.h : Grouped some structure fields to improve alignment and
cache efficiency.
The archive contains a diff compared to the original sources (thanks to svn).
Use the diff file to patch the original sources if you want to build DosBox
yourself.
Then, under sh :
CFLAGS="-O2" CXXFLAGS="-O2" ./configure --disable-dynamic-core --disable-opengl
--disable-dynrec --disable-dependency-tracking
And then :
- make
- Run "src/dosbox"
* Ideas for the future / to do
- Improve access to the x86 registers
- Activate OpenGL
- Check CDROM access
- Compare options -O2 and -O3
- Profile DosBox on Linux PPC (cache issues)
- Fix install of Win 3.1
- Fix color problems (x-ray, hugi)
- Fix MIDI : does not work even setting it in dosbox.conf with a directory
that contains instruments
- Fix FullScreen that send a 59 Hz signal and some screens does not go below 60
- Check usage of gamepads
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