Instruction Set

An instruction set describe the Assembly instruction that your computer can understand. Your instruction set will describe how much your computer is expressive (ie. the richness of the language with whom you talk to your computer).

Famous Instruction Set

• x86-64 (Il y a un plugin obsidian pour afficher un graphe de flow (en tant que canvas) à partir d’un fichier assembleur)
• ARM
• RISC

My Instruction Set v1

todo tester la fréquence maximale d’exécution de chaque instruction

Instructions using A or B share homologue instruction with immediate left and right. These instruction are suffixed with the letter L or R or the combination.

Instructions with the (opt) symbols are optional for the project. It’s a bonus if they are implemented.

ALU

Cycles	Instruction(8) A(8) B(8) R(8)	Description	Immediate
1	ADD A B R	R ← A + B	LR
1	SUB A B R	R ← A - B	LR
1	AND A B R	R ← A & B	LR
1	OR A B R	R ← A | B	LR
1	NOT A _ R	R ← ~A	L
1	XOR A B R	R ← A ^ B	LR
1	SHIFT A B R (opt)	R ← A >> B	LR
Maybe multiplication ???

COND

Cycles	Instruction(8) A(8) B(8) R(8)	Description	Immediate
1	JMP Adr(16) _	Jump to the RAM address denoted by Adr (modify the PC to Adr)	default for left and right
2		complete conditional jump : see instructions below
1	BEQ A B _	Test if A = B. IF true, do nothing, ELSE Jump over the next instruction (PC←PC+2). If you want to jump to a certain address only when condition is met you must follow this instruction by a JMP instruction, it will then takes two cycle to do what you want.	LR
1	BNEQ A B _ (opt)	Same with condition A != B	LR
1	BLE A B _ (opt)	Same with condition A ⇐ B	LR
1	BGE A B _ (opt)	Same with condition A >= B	LR
1	BL A B _ (opt)	Same with condition A < B	LR
1	BG A B _ (opt)	Same with condition A > B	LR

CTRL

Control the behavior of the computer

Cycles	Instruction(8) A(8) B(8) R(8)	Description	Immediate	BitCode
1	NOP _ _ _	Do nothing for one cycle	None	00000000
$\infty$	HALT _ _ _ (opt)	Stop the computer from running next instruction, maybe by cutting the clock to the PC	None
	INTER (opt)	todo interruption

HINT for interruption: INTER Adr(16) R Where Adr is the address of the function to call when an interrupt is triggered Where R indicate how an interrupt is triggered (eg: R → XAAAAAAA X indicate wheter to detect when input goes from 0 to 1 or from 1 to 0 the A bits is a mask that indicate the pin in the input register to watch)

Memory

The RAM and STK section share the memory with one block of ram also used to store the program and used by graphic card. You must be careful when addressing in this block not to overwrite things you don’t want like the program section, the stack section or the frame buffer.

RAM

Cycles	Instruction(8) A(8) B(8) R(8)	Description	Immediate
4	complete load from RAM	see instruction below
1	LDa Adr(16) R	Load data from RAM to R register. Because registers are only 8 bits, if you want to load the complete data stored in the RAM, you must write 4 instructions (LDa Adr reg1; LDb Adr reg2; LDc Adr reg3; LDd Adr reg4)	default for left and right
4	complete store in RAM	see instruction below
1	STa Adr(16) R	Store the data from register R to RAM. The same principle than LDa instruction is applied	default for left and right

STK

todo figure and explanation for functions

Cycles	Instruction(8) A(8) B(8) R(8)	Description	Immediate
1	SINIT Adr _ (opt)	Store Adr in the stack pointer register (describe the beginning of the stack in memory)	default for left and right
1	CALL Adr _ (opt)	Push current address+1 (in the PC) into the stack and jump to address Adr. Useful to call a function.	default for left and right
2	RET _ _ _ todo (opt)	Get N (the number of arguments) with a pop. Decrement the stack pointer by N. Pop into the PC	None
1	PUSH A _ _ (opt)	push value into the stack	L
1	POP _ _ R (opt)	pop value to register R	None

todo make a program that check ROM of microcode in order to prevent close-circuit and duplicated instruction.

My Instruction Set v2

The instructions are 16 bits wide. The bit 15 determines the instruction mode (Data or ALU).

The following registers are accessible :

• A which is also the RAM address
• V which is also the vRAM address
• *A which is the content of the RAM at address A accessible like any other register
• *V same for the vRAM
• D a temporary register

Tips

Si le temps presse et que je veux quand même faire de la vidéo, je peux loger un frame buffer dans la RAM

DATA Mode

The data Mode is enabled when the bit 15 of the instruction is set to 0.

In this mode the data given in the following 15 bits is directly sent to the A register.

Cycles	Instruction Pattern Mode [15] Data [14-0]	Description
1	0 X	A ← X

Note

With this technique it is only possible to transfer in one cycle numbers from 0 up to 32767 from the ROM into a register

ALU Mode

The data Mode is enabled when the bit 15 of the instruction is set to 1.

In this mode an operation specified by the opcode will be calculated using the srcA and srcB register and will be stored into the dest register.

Cycles	Instruction Pattern - Mode [15] - opcode/condition [14-12] - not used [11-9] - A [8-6] - B [5-3] - C [2-0]	Description
1	1 1$\diamond$ xx A B C	Operation C ← A $\diamond$ B
1	1 0$\star$ xx A B xxx	Condition if $\ast \ne JMP$ PC ← PC + 1 if A $\star$ B
The $\diamond$ operation is given by the following table :

Code	Name	Description
000	ADD	Addition
001	SUB	Substraction
010	AND	logical AND
011	OR	logical OR
100	XOR	exclusive logical OR
101	NOT	Complement (takes only the first operand)
110	SHL	logical bitshift to the left
111	SHR	logical bitshift to the right
The $\star$ relation is given by the following table :

Code tl eq gt	Relation $\star$
000	Never
001	>
010	=
011	>=
100	<
101	!=
110	⇐
111	Always

The different registers are indexed with this table :

Code	Register
000	A
001	*A
010	V
011	*V
100	D
101	not addressed
110	0 (zero constant)
111	1 (one constant)

todo réfléchir si des exclusions sont nécessaire par exemple entre les registres A et *A

Note

With this implementation, performing a jump takes 2 cycles : one for loading the jump address into A and one to perform the jump.

todo make a program that takes 16 bits and give a description of what the instruction is doing

todo interrupt, no op, multiplication, division