Dracula Unleashed (U) reboots to BIOS screen

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Use BIOS 2 for US consoles (haven't test BIOS 1)
2. Load Dracula Unleashed (U) rom (tried many different sources)
3. Rom is on USB 2 device, BIOS is on SD card

*Dracula Unleashed (E) using BIOS 2 for European consoles works fine.

What is the expected output? What do you see instead?
I expect the game to continue after the first screen that says Sega. Instead, 
it reboots to the BIOS screen

What version of the emulator are you using (official, SVN revision,...)?
1.7.3 (IOS 58), downloaded using Homebrew Browser

Please provide any additional information below (Emulator settings, Console
setting,...) Tried many different emulator settings arrangements and nothing 
works. Research on google indicates that some others have had issues loading 
this rom on PC's and that a "perfect sync" option fixed it, although I was not 
able to find that option in Genplus-GX. (on a side but related note... is there 
a way to put all the settings back to default easily? Since I've been mucking 
with them, I'm not sure where they were to begin with)

Original issue reported on code.google.com by theother...@gmail.com on 1 Mar 2013 at 1:37

[GoogleCodeExporter]

Genesis Plus GX does not have a "perfect sync" option because it does it by 
default, although not exactly the same as in other emus ( it is more optimized 
here).

I will look at it when I have some time, i am pretty sure I tested all US 
releases and this one used to work fine.

Original comment by ekeeke31@gmail.com on 1 Mar 2013 at 4:02

• Changed state: Accepted
• Added labels: Type-Defect, Priority-Medium, SCDEmulation

[GoogleCodeExporter]

You can reset the settings to default by deleting the config.ini file on your 
sdcard in genplus directory.

Original comment by ekeeke31@gmail.com on 1 Mar 2013 at 4:12

[GoogleCodeExporter]

It seems compatible with Sega CD BIOS v1.00 and v1.10 (Model 1).
Not sure why it resets with later model BIOS.

Original comment by ekeeke31@gmail.com on 2 Mar 2013 at 8:07

[GoogleCodeExporter]

It is indeed a synchronization issue between MAIN & SUB CPU. 
MAIN-CPU is reading the communication register and if SUB-CPU is not 
synchronized at that time, it won't update the value in time and MAIN CPU will 
read an incorrect value.

As a result, MAIN-CPU thinks the shared 2M Word-RAM is available and that it 
can run code from it, which later cause an exception because the Word-RAM does 
not hold yet any valid instructions. 

It should be fixed in a later revision once I check that the improved 
synchronization code does not cause any issues in other games or with different 
BIOS (some games, mainly those using unsafe synchronization methods like this 
one, are very sensitive to this)

Original comment by ekeeke31@gmail.com on 6 Apr 2013 at 6:45

• Changed state: Started

[GoogleCodeExporter]

Fixed in r770

I improved the synchronization between the two CPU as well as polling loop 
detection, and took the time to verify that all existing games boot fine and go 
to gameplay with either Model 2 or Model 1 BIOS.

Original comment by ekeeke31@gmail.com on 19 Apr 2013 at 2:47

• Changed state: Verified