TGP:Index

Generalities

Usage of this CPU

The mb86232/86233/86234, 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.

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" 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.