Re: [新聞] (WIP) David Haywood's Homepage
2015.06.10
"Choplifter ’92"
Sega’s Air Rescue is a spiritual successor to the game Choplifter, you fly
around surrounded by enemy vehicles while attempting to land to pick up
hostages. Jaleco used the same concept for their overhead perspective ‘
Desert War’ too.
The twist with Air Rescue is that while Choplifter is a side-on view, and
Desert War is an overhead view the entire game here is presented in a 3d
perspective using zoomed sprites.
The game used Sega’s System 32 platform and has been partially emulated in
MAME for a long time now. I say partially emulated because we needed some
hacks to get it running. The thing with the Air Rescue hardware is that it
actually uses 2 stacks of System 32 PCBs which are directly connected using a
bridge board placed under the rom board. That bridge board contains RAM which
is shared between the two System 32 stacks.
With the real hardware if either of the System 32 PCBs or the bridge board
fails / are missing the game does not boot, it is designed to work in the 2
screen, 2 player cabinet it shipped in only. MAME hacked around this faking
the response from the 2nd PCB stack in order to avoid emulating it, this
however had some unwanted side effects.
For a start, the title screen was cut in half the first time of showing, and
subsequent times the single screen title that is meant to be used while the
other player is playing was shown. This also meant the intro sequence was
never shown in the attract mode. More importantly half the gameplay was
missing, the dual screen setup means the game can actually be played as a
co-op game in addition to being a single player game, in co-op mode each
player flies their own helicopter around the same arena and the number of
hostages to rescue + number of enemies is increased to maintain the same
level of challenge.
MAME has a nice device based system these days, so by promoting an entire
System 32 PCB to be a device, allowing for two to be added to a driver with
the shared RAM added just like any other shared RAM, I was able to quite
simply emulate this properly.
Note this isn’t a ‘network’ game as such, there are no network cables, it’
s a simple case of doubled up hardware. Sega would later refine their system
into the ‘multi32′ board which was capable of driving 2 screens on it’s
own with half the video capability on each, these full-fat setups were
obviously more expensive. The multi32 system was already emulated with both
screens (although I do need to look at some bugs that were introduced way
back when Aaron rewrote the driver then never fixed the reported bugs)
http://mamedev.emulab.it/haze/pics2015/arescue_1.png
I’ve also made a video, note the sound is rather chaotic because you’re
hearing the output from both monitors, which often end up playing the same
tune with a slight delay causing an echo effect, this would sound less harsh
if sat in front of the speakers for each screen on the cabinet.
F1 Exhaust Note uses the exact same type of link board and benefits in the
same way, note how you can see the position of the other players car marked
on you screen with an arrow in the final 2 gameplay shots.
http://mamedev.emulab.it/haze/pics2015/f1en_1.png
F1 Super Lap is a linked game instead and hasn’t been touched.
Bonus Trivia
For the curious, Sega also released an ‘Air Rescue’ game for the Sega
Master System, this 8-bit game has little resemblance to the arcade and plays
more like a traditional sequel to Choplifter. With the MAME/MESS merger of
0.162 you can now play this in MAME using the launch syntax of “mame smspal
airresc”
http://mamedev.emulab.it/haze/pics2015/sms_air_1.png
來源：http://mamedev.emulab.it/haze/2015/06/10/choplifter-92/
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