11-19-2013, 08:01 AM
Yeah I looked at the RACE code, and it returns 0x0 if you request 0x4000 or 0x4001.
I'm stepping through the real BIOS right now, and what I'm seeing is an infinite loop that waits for (0x4000) to be something other than 0.
... disasembly of the real bios ...
00009798: 1D 9D98FF CALL 0FF989Dh ; Call 989D Setup some type of Clock memory function
0000979C: C2 004000 3F 00 CP (004000h),000h ; [0x4000] == 0 (Noise Chip + Left Volume read)
000097A2: 66 F8 JR EQ/Z,000979Ch ; If we are 0x0 (RACE returns this), loop forever.
My next step is putting this in a rom, loading it on my NGPC, and testing various states of write to noise chip, read (4000h), write to tone chip, read (4001h).
I'm stepping through the real BIOS right now, and what I'm seeing is an infinite loop that waits for (0x4000) to be something other than 0.
... disasembly of the real bios ...
00009798: 1D 9D98FF CALL 0FF989Dh ; Call 989D Setup some type of Clock memory function
0000979C: C2 004000 3F 00 CP (004000h),000h ; [0x4000] == 0 (Noise Chip + Left Volume read)
000097A2: 66 F8 JR EQ/Z,000979Ch ; If we are 0x0 (RACE returns this), loop forever.
My next step is putting this in a rom, loading it on my NGPC, and testing various states of write to noise chip, read (4000h), write to tone chip, read (4001h).