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bsnes is a Super Nintendo (SNES) emulator focused on performance, features, and ease of use.
2d73086569
byuu says:
You guys are going to hate the hell out of this one. It's twenty hours
of non-stop work, no exaggeration at all. Started at 4AM, just wrapped
up now at 8PM.
I rewrote the entire memory subsystem.
Old system:
65536 pages that map 256 bytes each
Mapping a new page overwrites old page
Granularity capped at 256 bytes minimum, requiring ST-001x to map
60:0000-00ff instead of 60:0000,0001
Classes inherit from MMIO and Memory, forcing only one mappable function
per class, and fixed names
MMIO sub-mapper inside memory: 00-3f:2000-5fff for one-byte granularity
Can dynamically change the map at run-time, MMC register settings
perform dynamic remapping
New system:
XML mapping is still based around banklo-bankhi:addrlo-addrhi, as that
shapes almost everything on the SNES very well
Internally, 2048 pages that map 8192 bytes each
Pages are vectors, scans O(n) from last to first (O(log n) would not
help, n is never > 3)
Can multi-cast writes, but not reads [for the obvious reason of: which
read do you return?]
Can map reads and writes separately
Granularity of one for entire 24-bit address range, no need for MMIO
- whatever is in XML is exactly what you get
Read/Write tables bind function callbacks, so I can have any number of
functions with any names from any classes with no inheritance (no
more uPD7725DR, uPD7725SR helpers, etc)
Less memory usage overall due to less tables [ I tried 16 million tables
and it used 2GB of RAM >_o ]
Cannot dynamically change the map at run-time, MMC read/write functions
perform address translation [worse average case speed, better worst
case speed]
Now the hate me part, functors can't beat virtual functions for speed.
There are speed penalties involved:
-4.5% on average games
-11% on SuperFX games (SFX has its own bus)
-15% on SA-1 games (SA-1 has two buses)
Of course the two that need the speed the most get the biggest hits.
I'm afraid there's really not a lot of wiggle room to boost speed back
up.
I suppose one bright spot is that we can much more easily try out
entirely new mapping systems now, since the dynamic portions have been
eliminated.
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| bsnes | ||
| shaders | ||
| snesfilter | ||
| snespurify | ||