TGP:Index

Generalities

Usage of this CPU

The MB86232/86233/86234/FDSP-4, also known as the TGP, is used in Sega Model 1, 2 and 2A. There are two, one is used as a T&L unit, the other as a coprocessor. In Model 1, both programs are internal to the CPUs. In Model 2/2A, the T&L program is internal while the coprocessor program is uploaded.

Model 2B uses a pair of SHARCs to replace the TGPs, 2c a pair of TGPx4 (MB86235, FDSP-5 in spirit but not in name), which only has the name in common with the original TGP.

Known information

The datasheet is the best information we have at that point. Grab it, read it, it won't be repeated in here. The copy/paste eagerness of the original author that makes us miss the op-B operations is a pity though. Other sources:

• An IEEE article: "Implementation Of A 4.8 Kbps Voice Codec Based On Pitch-Synchronous DFT Coding".
• US patent 5,099,417 may be related to the chip. Type is correct (32 bits DSP), time is correct. DSP-3 was 16 bits, and TGPx4 was 64bits. Patents are quite hard on the reading though.

The CPU seems to do everything on 32-bits words, so endianness is irrelevant. The main CPU of Model 2 (i960) is little-endian though, so the program are stored that way.

Known programs

One can use an emulator to get the uploaded TGP programs, but the simplest way is probably to get them from the ROMs themselves. Use the MAME source to check which files to use and the interleave. Sizes are in 32bits words. As the md5 shows, some programs are identical.

Game	Region	Address	Size	MD5
zeroguna	CPU1	008cc4	b28	3164f056a727dbd84966dabafa542040
vf2	CPU1	003e90	eda	514f0ebd82cc03a5c99ff0c20227aa46
srallyc	CPU1	05ae94	682	ca706c08f84f1c721d5401ea0e50988a
manxtt	CPU1	0787e8	6b6	2a9f8b8e5cd4d71527d75b07eb5b45e0
skytargt	USER1	e7114c	b2b	12c49cd5e99ae89b7c1d7d8521ca3443
vcop2	CPU1	05d480	6f2	59675510722a18b847eec08f75d55d05
dynamcop	CPU1	0b6084	e80	2389379b14042147626cd83cfb98811f
dyndeka2	CPU1	0b6074	e80	2389379b14042147626cd83cfb98811f
pltkidsa	CPU1	01a378	94b	5fbd0626f6cb73ced9026b420873a27b
doaa	CPU1	009664	b2b	12c49cd5e99ae89b7c1d7d8521ca3443
daytona	USER1	800020	7e8	8b6f2d1decf8a6be6c4c9005d8361aa5
vcop	CPU1	0070c0	7e8	dff894ca077cb02cb66e6d1dec8e9020
desert	CPU1	0016a0	7e8	8b6f2d1decf8a6be6c4c9005d8361aa5

Subset encodings

Registers

Register numbers are encoded in 3+6 bits. The first 3 bits are some kind of type.

Type 0 and 3 address the same registers. 3 adds a "Hi, I'm the destination of the move" twist to it though. Here are the known registers:

Value	Register
00-0f	Register file
10-12	a, a.e, a.m
13-15	b, b.e, b.m
16-18	c, c.e, c.m
19-1b	d, d.e, d.m
1c	p
21	fifo_in
22	fifo_out

Type 6 looks like special registers. Only value 21 is known as being some kind of indirect access register.

ALU op-A operations

ALU operations are encoded in 6 bits. According to the datasheet the shift operations are not supposed to be there but should be opcodes by themselves.

Value	Type	Operation	Value	Type	Operation	Value	Type	Operation	Value	Type	Operation
00 000000		nop	10 010000	f32	p = a * b	20 100000	?	?	30 110000	int	a = a >> c
01 000001		nop	11 010001	f32	p = a * b	21 100001	?	?	31 110001	int	a = a >> d
02 000010	int	c = c & a	12 010010	f32	c = c + p, p = a * b	22 100010	?	?	32 110010	?	?
03 000011	int	d = d & a	13 010011	f32	d = d + p, p = a * b	23 100011	?	?	33 110011	?	?
04 000100	?	?	14 010100	f32	c = c - p, p = a * b	24 100100	?	?	34 110100	i24	c = c + a
05 000101	?	?	15 010101	f32	d = d - p, p = a * b	25 100101	?	?	35 110101	i24	d = d + a
06 000110	?	?	16 010110	?	?	26 100110	?	?	36 110110	i24	c = c - a
07 000111	?	?	17 010111	?	?	27 100111	?	?	37 110111	i24	d = d - a
08 001000	?	?	18 011000	f32	c = a + b	28 101000	f32	c = a - b	38 111000	?	?
09 001001	?	?	19 011001	f32	d = a + b	29 101001	f32	d = a - b	39 111001	?	?
0a 001010	?	?	1a 011010	f32	c = p, p = a * b	2a 101010	?	?	3a 111010	?	?
0b 001011	?	?	1b 011011	f32	d = p, p = a * b	2b 101011	?	?	3b 111011	?	?
0c 001100	f32	c = c + a	1c 011100	?	?	2c 101100	?	?	3c 111100	?	?
0d 001101	f32	d = d + a	1d 011101	?	?	2d 101101	?	?	3d 111101	?	?
0e 001110	f32	c = c - a	1e 011110	?	?	2e 101110	int	a = a << c	3e 111110	?	?
0f 001111	f32	d = d - a	1f 011111	?	?	2f 101111	int	a = a << d	3f 111111	?	?

Known missing: xor, not, neg, abs, comparisons (sub). Operations 36 and 37 (at least) are known to set flags though.

ALU op-B operations

Unknown, should be somewhere in the "single move" and "dual move" pattern.

Known instructions

Single move

Single move, y=x,op-A

1f	1e	1d	1c	1b	1a	19	18	17	16	15	14	13	12	11	10	0f	0e	0d	0c	0b	0a	09	08	07	06	05	04	03	02	01	00
000111						op-A						??		source register									destination register

'??' is usually, but not always, 11. The source can actually be the destination when its type is '3', cf registers description. There is supposed to be an op-B somewhere in there.

Dual move

Dual move, r1=x, r2=y,op-A

1f	1e	1d	1c	1b	1a	19	18	17	16	15	14	13	12	11	10	0f	0e	0d	0c	0b	0a	09	08	07	06	05	04	03	02	01	00
000000						op-A						type?		register 1									register 2

Possible types found in the datasheet are load A&B, load A&C, load A&D, load A store C, load A store D, load C store C, load D store D. 2 bits are not enough. Also, there should be an op-B somewhere.

Branches

Branches encoding

1f	1e	1d	1c	1b	1a	19	18	17	16	15	14	13	12	11	10	0f	0e	0d	0c	0b	0a	09	08	07	06	05	04	03	02	01	00
1011111							condition					type			0	destination

Branches types

Value	0	1	2	3	4	5	6	7
Type	branch absolute	branch indirect	bsr absolute	bsr indirect	?	rts	?	rti

Conditionals (known incorrect)

Value	00	01	02	06	10	11	12	16
Type	==	<=	=>	never	!=	>	<	always

One or both of types 4/6 may be load conditional. For absolute branches, the destination is the 16-bits address. For the indirect one, encoding is unknown except for 40xx which designates a register. The conditional values are known wrong except for 6/16, they'll be fixed later when the code around them is sorted a little better. The top bit is the "if/unless" bit, inverting the condition.

Load 24-bits integer

Load immediate 24bits

1f	1e	1d	1c	1b	1a	19	18	17	16	15	14	13	12	11	10	0f	0e	0d	0c	0b	0a	09	08	07	06	05	04	03	02	01	00
001110						dest		value

Destinations

Value	0	1	2	3
Register	p	a	b	d

Load floating point

Load immediate 24bits

1f	1e	1d	1c	1b	1a	19	18	17	16	15	14	13	12	11	10	0f	0e	0d	0c	0b	0a	09	08	07	06	05	04	03	02	01	00
010110						dest		value (8 bits only for exponent)

Destinations

Value	0	1	2	3
Type	c.exponent	c.mantissa	d.exponent	d.mantissa