When the Saturn is first powered on, is it true that the master SH2 begins executing at $00000200 ?
The opcode there (in the BIOS) is $BEB0 which seems to branch around to the $FFFFFFxx range. What is really supposed to be going on?
I was just working on a little SH2 emu (don't hold your breath for any results ) and am stumped already.
Any docs that I should be looking at? TIA
CyberWarriorX
Dec 8, 2005
When either SH2 is started, it fetches the initial PC from offset 0 in bios, and the initial SP(R15) from offset 0x4 in bios.
That opcode is actually "BSR 0x20000380"
I still say the best doc for programming a sh2 emulator is the sh2 programmer's manual. And of course the SH7604 hardware manual. You can get them both from antime's website.
Cyber Warrior X
antime
Dec 8, 2005
To be precise, at power-on the PC will be loaded from vector 0 of the Exception Vector Table, and the initial value of the VBR is specified to be zero.
Your mistake is that the Saturn is a big-endian machine, so the value you're looking at is 0xb0be, not 0xbeb0.
DamageX
Dec 8, 2005
doh! OK, I should be back on track now, thanks.
I wrote some code about a year ago and then didn't do anything further with it until this week. I had forgotten some important details during that time. (Plus, it's evident that I didn't really know what I was doing in the first place.)
) and am stumped already. 
