mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-11-13 22:35:10 +01:00
313 lines
14 KiB
Plaintext
313 lines
14 KiB
Plaintext
----------------------------------------------
|
|
SEGA GENESIS EMULATOR SAVE STATE REFERENCE
|
|
Third Edition (February 23, 2002)
|
|
Bart Trzynadlowski
|
|
----------------------------------------------
|
|
|
|
|
|
---------
|
|
About
|
|
---------
|
|
|
|
The aim of this reference is to document the save state and backup RAM formats
|
|
of the various Sega Genesis emulators out there. Distribute this document
|
|
freely, but please keep it unmodified. If you use any of this information,
|
|
give credit to the contributors and me.
|
|
|
|
The following people contributed directly and/or indirectly:
|
|
|
|
- Charles MacDonald (supplied most of the Genecyst save state information)
|
|
- Jeffrey Quinn (found the SSP and USP in Genecyst states)
|
|
- Steve Snake (contributed Genecyst and KGen98 information)
|
|
- Langoustator (supplied YM2612 register information and some KGen98 data)
|
|
|
|
More information on any of the formats, especially the KGen format, would be
|
|
appreciated. You can reach me at bart@dynarec.com or visit my web site at
|
|
http://www.dynarec.com/~bart.
|
|
|
|
A "byte" is considered to be 8 bits, a "word" is 16 bits, and a "double word"
|
|
is 32 bits.
|
|
|
|
Change History
|
|
--------------
|
|
|
|
February 12, 2002: Second Edition
|
|
- Added some Genecyst and KGen save state information
|
|
supplied by Steve Snake
|
|
- Corrected some typos
|
|
|
|
April 11, 2001: First Edition
|
|
- Initial public release
|
|
|
|
|
|
------------------------------
|
|
Genecyst Save State Format
|
|
------------------------------
|
|
|
|
The Genecyst save state format (GST) is used by various emulators. The files
|
|
use the extensions GS0-GS9 depending on the save slot. The information in this
|
|
section has been validated against Genecyst v0.32b. I believe Version X.XX is
|
|
very similar, if not the same, but I would appreciate confirmation.
|
|
|
|
Offset Range: Description:
|
|
------------- ------------
|
|
0x00000-0x00002 Signature: "GST"
|
|
0x00006 0xE0, apparently used to validate file integrity
|
|
0x00007 0x40, apparently used to validate file integrity
|
|
0x00080-0x0009F 68K registers D0-D7
|
|
0x000A0-0x000BF 68K registers A0-A7
|
|
0x000C8-0x000CB 68K PC
|
|
0x000D0-0x000D1 68K SR
|
|
0x000D2-0x000D5 68K USP
|
|
0x000D6-0x000D9 68K SSP
|
|
0x000FA-0x00112 VDP registers (0-23, 1 byte each)
|
|
0x00112-0x00191 CRAM
|
|
0x00192-0x001E1 VSRAM
|
|
0x001E4-0x003E3 YM2612 registers
|
|
0x00404-0x00437 Z80 registers: AF, BC, DE, HL, IX, IY, PC, SP, AF',
|
|
BC', DE', HL', I (stored as a double word each.) R is
|
|
not supported and IM is presumed to be 1
|
|
0x00438 Z80 IFF1 (IFF2 is assumed to be the same)
|
|
0x00439 Z80 status (0 = stopped, 1 = running), probably has
|
|
something to do with BUSREQ
|
|
0x0043C-0x0043F Z80 window bank
|
|
0x00474-0x002473 Z80 RAM
|
|
0x02478-0x12477 68K RAM
|
|
0x12478-0x22477 VRAM
|
|
|
|
Steve Snake sent me word that 0x00434 (byte) is the Z80 I register and
|
|
0x00437 (byte) is the Z80 interrupt mode. This conflicts with my data
|
|
which says 0x00434 is a double word where I is stored. I'm not sure which
|
|
is correct.
|
|
|
|
All data is in little endian format except for 68K RAM, VSRAM, and VRAM, which
|
|
are in big endian format. Areas not mentioned should be kept 0.
|
|
|
|
Locations 0x00006 and 0x00007 are not completely understood. Genecyst expects
|
|
them to be 0xE0 and 0x40, respectively. This has been observed in Genecyst
|
|
v0.20, v0.32b, and vX.XX. Many emulators avoid saving these bytes and Genecyst
|
|
refuses to load their states.
|
|
|
|
The USP and SSP are tricky. If the supervisor bit in SR is set, only the USP
|
|
is saved at 0x000D2, the SSP at 0x000D6 is set to 0. If the supervisor bit is
|
|
cleared, both the USP at 0x000D2 and the SSP at 0x000D6 are saved. A7 is also
|
|
the current stack pointer (SSP if supervisor mode, USP if user mode.)
|
|
|
|
Information on the YM2612 registers was sent to me by Langoustator who says it
|
|
is valid for Gens save states and is assumed to be valid for true Genecyst
|
|
states as well. None of it has been verified by me, but I'll assume it is
|
|
correct:
|
|
|
|
- 0x001E4-0x00205: Apparently unused
|
|
- 0x00206-0x00213: General registers (not channel specific.) There are
|
|
only 9 registers at: 0x206, 0x208, 0x209, 0x20A,
|
|
0x20B, 0x20C, 0x20E, and 0x20F.
|
|
- 0x00214-0x002E3: Channel-specific registers for channels 1-3. They are
|
|
stored in 4 byte groups with each group layed out like
|
|
this:
|
|
|
|
First byte = Channel 1
|
|
Second byte = Channel 2
|
|
Third byte = Channel 3
|
|
Fourth byte = Unused (0)
|
|
|
|
The registers only appear to end at 0x0029B and the
|
|
rest of the area (from 0x0029C-0x002E3) is unused.
|
|
|
|
- 0x002E4-0x00313: Apparently unused
|
|
- 0x00314-0x003E3: Channel-specific registers for channels 4-6. They are
|
|
stored in 4 byte groups like the channel 1-3 registers.
|
|
They end at 0x0039B and the rest of the area (from
|
|
0x0039C-0x003E3) is unused.
|
|
|
|
More information is needed, especially on (but not limited to) the following:
|
|
|
|
- PSG state
|
|
- Internal VDP information (control port status, VDP RAM pointer, etc.)
|
|
|
|
|
|
------------------------------
|
|
Genecyst Backup RAM Format
|
|
------------------------------
|
|
|
|
Genecyst saves backup RAM in files with the GSV extension. They simply contain
|
|
the backup RAM in little endian format. The files do not always have an even
|
|
number of bytes.
|
|
|
|
Even if backup RAM only appears in the odd or even addresses, Genital saves
|
|
the unused bytes (which should be 0.)
|
|
|
|
Those emulators which keep the 68K address space in little endian format can
|
|
support GSV files easily: simply copy the contents of the files unmodified to
|
|
the backup RAM area.
|
|
|
|
A few emulators, including Genital, use the GSV format.
|
|
|
|
|
|
----------
|
|
KGen98
|
|
----------
|
|
|
|
There is no official information on KGen's save state format, so I decided to
|
|
take it upon myself to try reverse engineering the format. Due to a lack of
|
|
time, I have not been able to learn more than is shown here. It might be
|
|
enough to load states, but isn't enough to save them.
|
|
|
|
The below information applies to KGen98 v0.4b, I do not know if it applies to
|
|
other versions of KGen and KGen98. Any more information is most welcome.
|
|
|
|
Offset Range: Description:
|
|
------------- ------------
|
|
0x00000-0x00002 Signature: "KSS"
|
|
0x00003 Must be 0x1, also part of the signature
|
|
0x00004-0x00005 ROM checksum, word sized
|
|
0x00008-0x00096 Path to ROM (zero terminated), when path is at maximum
|
|
length, 0x96 contains the last character of the path
|
|
0x00097 Always 0
|
|
0x00098-0x02097 Z80 RAM
|
|
0x02098-0x12097 68K RAM
|
|
0x12098-0x22097 VRAM
|
|
0x22098-0x22117 CRAM
|
|
0x22298-0x222E7 VSRAM
|
|
0x2235C-0x2237B 68K registers D0-D7
|
|
0x2237C-0x2239B 68K registers A0-A7
|
|
0x2239C-0x2239F 68K SP (if supervisor mode: USP, if user mode: SSP)
|
|
0x223A0-0x223A3 68K PC
|
|
0x223A4-0x223A7 68K SR
|
|
0x223A8-0x223AB Previous SR value (Steve says only the high byte is
|
|
necessary), used to detect changes between privilege
|
|
levels
|
|
0x223AE-0x223C5 VDP registers (0-23, 1 byte each)
|
|
0x2273E-0x227?? Data written to VDP control port
|
|
0x22742-0x22743 Control port half: if only one word of a 2-word
|
|
command was written, it is stored here
|
|
0x22748-0x22749 Current VDP RAM address
|
|
|
|
The checksum, 68K RAM, VRAM, CRAM, and VSRAM are stored in big endian format.
|
|
Everything else is in little endian format.
|
|
|
|
I believe location 0x2273E is a little endian double word. There is plenty of
|
|
important internal VDP and FM data kept at the end of the file. I haven't
|
|
found the meaning of all of it. Also, the path to the save state's ROM file is
|
|
saved near the beginning of the file.
|
|
|
|
|
|
-----------------
|
|
Genital v1.2+
|
|
-----------------
|
|
|
|
Starting with Version 1.2, Genital save state files use a version numbering
|
|
system independent from Genital itself. Save states with different major
|
|
version numbers are not compatible. The minor version number indicates changes
|
|
in the format which do not affect backwards compatibility.
|
|
|
|
Version 1.0 of this new GNS format is described below:
|
|
|
|
Offset Range: Description:
|
|
------------- ------------
|
|
0x00000-0x00002 Signature: "GNS"
|
|
0x00003 Format major version
|
|
0x00004 Format minor version
|
|
0x00005-0x00007 Reserved (always keep 0)
|
|
0x00008-0x00057 68K registers and status (from Genital68K context)
|
|
0x00058-0x00077 68K pending interrupts (from Genital68K context)
|
|
0x00078-0x10077 68K RAM
|
|
0x10078-0x20077 VRAM
|
|
0x20078-0x200F7 CRAM
|
|
0x200F8-0x20147 VSRAM
|
|
0x20148-0x201A7 VDP registers (0-23; double word each)
|
|
0x201A8-0x201BF VDP internal status data (taken directly from VDP
|
|
context: ctrlport_mode, access_mode, addr, addr_top,
|
|
dma_mode, and status_register; double word each)
|
|
0x201C0-0x201C3 VDP horizontal interrupt timer
|
|
0x201C4-0x201C7 Reserved (always keep 0)
|
|
0x201C8-0x201CB Z80 BUSREQ
|
|
0x201CC-0x201EB Z80 registers (word each: AF, BC, DE, HL, IX, IY, PC, SP,
|
|
AF', BC', DE', HL', IR, IM, IFF1, IFF2)
|
|
0x201EC-0x221EB Z80 RAM
|
|
|
|
Everything is stored in little endian format.
|
|
|
|
The 68K registers and status come directly from the Genital68K context, occupy
|
|
a double word each, and are ordered:
|
|
|
|
D0-D7, A0-A7, SP, SR, PC, status
|
|
|
|
The "SP" relies on the privilege mode. If in supervisor mode, this is the USP
|
|
(and the SSP is in A7.) If in user mode, this is the SSP (and the USP is in
|
|
A7.) Please read the Genital68K (now Turbo68K) documentation for information
|
|
on what the "status" is (http://www.dynarec.com/~bart/turbo68k.)
|
|
|
|
The first 7 elements pending interrupt array correspond to interrupt levels
|
|
1-7. Each element, a double word in size, contains the vector of the interrupt
|
|
that is pending. The eighth element is the number of interrupts pending.
|
|
Again, see the Genital68K documentation for more information.
|
|
|
|
The VDP internal status comes directly from Genital's VDP context. The
|
|
"ctrlport_mode" indicates which part of a command the control port expects. If
|
|
0, it expects the first part, otherwise the second. The access_mode is just
|
|
the VDP's CD bits which indicate VRAM write, CRAM write, VSRAM write, VRAM
|
|
read, etc. The VDP RAM current address is stored in the "addr" element. Bits
|
|
15 and 14 of the VDP RAM address are stored in bits 1 and 0 of "addr_top."
|
|
These are used to emulate a peculiar feature of the VDP. The "dma_mode" stores
|
|
the DMA mode bits. The "status_register" is the VDP Status Register.
|
|
|
|
The "horizontal interrupt timer" is the count-down timer which triggers
|
|
horizontal interrupts.
|
|
|
|
|
|
---------------------------
|
|
Genital (v1.0 and v1.1)
|
|
---------------------------
|
|
|
|
The Genital save state format (GNS) was introduced in Genital v1.0 and was
|
|
completely changed by v1.2. Versions 1.0 and 1.1 used the format described
|
|
below.
|
|
|
|
Offset Range: Description:
|
|
------------- ------------
|
|
0x00000-0x0FFFF 68K RAM
|
|
0x10000-0x1FFFF VDP VRAM
|
|
0x20000-0x21FFF Z80 RAM
|
|
0x22000-0x2207F VDP CRAM
|
|
0x22080-0x220CF VDP VSRAM
|
|
0x220D0-0x220EF 68K registers A0-A7
|
|
0x220F0-0x220F3 68K SP (if supervisor mode: USP, if user: SSP)
|
|
0x220F4-0x22113 68K registers D0-D7
|
|
0x22114-0x22117 68K SR
|
|
0x22118-0x2211B 68K PC
|
|
0x2211C-0x2214F Z80 registers: AF, BC, DE, HL, IX, IY, PC, SP, AF',
|
|
BC', DE', HL', IR (stored as a double word each)
|
|
0x22150-0x22153 Z80 BUSREQ
|
|
0x22154-0x221B3 VDP registers (0-23, double word each)
|
|
0x221B4-0x221B7 VDP control port mode
|
|
0x221B8-0x221BB VDP RAM address pointer
|
|
0x221BC-0x221BF VDP RAM access mode
|
|
0x221C0-0x221C3 VDP DMA mode
|
|
0x221C4-0x221C7 VDP Status Register
|
|
0x221C8-0x221CB VDP HV counter
|
|
0x221CC-0x221CF VDP Horizontal Interrupt timer
|
|
0x221D0-0x221D3 VDP Control Port A15, A14
|
|
0x221D4-0x221DA Reserved (7 bytes; should be 0)
|
|
0x221DB Major version number of Genital
|
|
0x221DC Minor version number of Genital
|
|
0x221DD-0x221DF Signature: "GNS"
|
|
|
|
The 68K RAM, VRAM, CRAM, and VSRAM are stored in big endian format. Everything
|
|
else is in little endian format.
|
|
|
|
The VDP RAM address pointer is the current VRAM, CRAM, or VSRAM address. The
|
|
VDP RAM access mode is just the CD bits in a VDP command which indicate
|
|
whether the VDP is in VRAM write mode, VRAM read mode, CRAM write mode, etc.
|
|
|
|
The VDP Control Port mode indicates which part of the command the VDP is
|
|
expecting. This is the "pending flag" described by Charles MacDonald's VDP
|
|
document. The A15, A14 bits are those last written to the control port. When
|
|
the first word of an address set command is written, these bits are used to
|
|
fill in A15, A14. They are stored in bits 1 and 0 of the GNS double word.
|
|
|
|
The major and minor version numbers reflect the version of Genital which
|
|
produced the save state. For example, if the state was created with Genital
|
|
v1.0, the major version would be 1 and the minor would be 0. The signature
|
|
must be "GNS" in ASCII or the save state will be deemed corrupt.
|