Wrapper/shim library to drive another ddrio in a dedicated
IO thread. Depending on the other ddrio backend used, this
can significantly improve performance while staying
compatible to the existing ddrio API interface
This turned out to be a good solution to solve performance
problems when running MAME with ddrio-p3io that is
(currently) implemented with synchronous IO calls that are
very costly: ~12 ms for a write over the ACIO protocol, ~4 ms
for a read using an IOCTL. As this already adds up to nearly
a full frame (60 fps) regarding latency, there isn't a lot
of time left to do other stuff in a synchronous update loop.
MAME's performance was unstable and dropped all the time below
100%. The result was a choppy gameplay experience.
Combining ddrio-async with ddrio-p3io, the combined backend
is able to drive inputs/outputs at a rate of ~250hz = ~4
updates per frame. This results in an average input latency
of ~4 ms which is as good as it can get with the p3io
hardware's performance limitations that I measured (see
the 4 ms for the IOCTL mentioned above).
This is more than good enough as as update frequency of
the 573 hardware is slightly less than that (I got told
something ~180 hz?).
tl;dr: Gameplay on MAME is great, smooth frame rate, IO feels
amazing and responsive.
icex2