CPUProject

CPU project is one of the projects designed in department of computer engineering at TTU as a lab project. The main aims of this project are:

• Developing a generic CPU without any fancy feature
• Writing a compiler for it
• Compiling GCC for this architecture
• Booting a light linux on it

CPU Design

Functionality Requirements

The CPU is supposed to be able to perform the following operations:

• Addition/Subtraction
• Increment/Decrement
• Arithmetic and Logical Shift
• Bitwise AND, OR, XOR and NOT
• Negation
• Load/Store
• Unconditional Branch (jump)
• Branch if zero / Branch if Overflow / Branch if Carry
• Clear Registers/Flags
• PUSH / POP
• NOP/HALT

Architecture

Instruction Format

Our CPU's instuction has 8 bit of upcode and one operand that can be as long as 32 bit. First 3 bits of OPcode are at the moment reserved.

Instruction Set (IS)

The following instrcutions designed for the CPU:

Instruction	Register Transfer Language	OpCode	DPU Command	Data To DPU	MemAddress	Next PC
Add_A_B	A <-- A + B	Example	00 000 0000 10	----	----	PC_out+1
Add_A_Mem	A <-- A + Mem[Operand]	Example	00 000 0000 00	----	Operand	PC_out+1
Add_A_Dir	A <-- A + Operand	Example	00 000 0000 01	Operand	----	PC_out+1
Sub_A_B	A <-- A - B	Example	00 000 0001 10	----	----	Example
Sub_A_Mem	A <-- A - Mem[Operand]	Example	00 000 0001 00	----	Operand	PC_out+1
Sub_A_Dir	A <-- A - Operand	Example	00 000 0001 01	Operand	----	PC_out+1
IncA	A <-- A + 1	Example	00 000 0000 11	----	----	PC_out+1
DecA	A <-- A - 1	Example	00 000 0001 11	----	----	PC_out+1
And_A_B	A <-- A and B	Example	00 000 0100 10	----	----	PC_out+1
OR_A_B	A <-- A or B	Example	00 000 0101 10	----	----	PC_out+1
XOR_A_B	A <-- A xor B	Example	00 000 0110 10	----	----	PC_out+1
FlipA	A <-- not (A)	Example	00 000 1100 00	----	----	PC_out+1
NegA	A <-- not(A) + 1	Example	Example	----	----	PC_out+1
Jmp	PC <-- Operand	Example	Example	----	----	Depends
JmpZ	if Z = 1: PC <-- Operand	Example	Example	----	----	Depends
JmpOV	if OV = 1: PC <-- Operand	Example	Example	----	----	Depends
Jmp_rel	PC <-- PC + Operand	Example	Example	----	----	Depends
JMPEQ	if EQ = 1: PC <-- Operand	Example	Example	----	----	Depends
ClearZ	Z <--- 0	Example	Example	----	----	PC_out+1
ClearOV	OV <--- 0	Example	Example	----	----	PC_out+1
LoadPC	PC <---- A	Example	Example	----	----	A
SavePC	A <---- PC	Example	Example	PC	----	PC_out+1
ShiftArithR	A <-- A(7) & A(7 downto 1)	Example	Example	----	----	PC_out+1
ShiftArithL	A <-- A(7) & A(5 downto 0)& '0'	Example	Example	----	----	PC_out+1
ShiftA_R	A <-- A(6 downto 0)& '0'	Example	Example	----	----	PC_out+1
ShiftA_L	A <-- '0' & A(7 downto 1)	Example	Example	----	----	PC_out+1
Load_A_Mem	A <-- Mem[Operand]	Example	Example	----	Operand	PC_out+1
Store_A_Mem	Mem[Operand] <-- A	Example	00 000 0010 --	----	Operand	PC_out+1
Load_B_Dir	B <-- Operand	Example	00 000 0010 --	Operand	----	PC_out+1
Load_B_Mem	B <-- Mem[Operand]	Example	00 000 0010 --	----	Operand	PC_out+1
JmpC	if C = 1: PC <-- Operand	Example	00 000 0010 --	----	----	Depends
ClearC	C <--- 0	Example	00 000 0010 --	----	----	PC_out+1
ClearACC	ACC <-- 0	Example	Example	----	----	PC_out+1
RRC	A <-- C & A(7 downto 1) ,C<-- A(0)	Example	Example	----	----	PC_out+1
RLC	A <-- A(6 downto 0) & C ,C<-- A(7)	Example	Example	----	----	PC_out+1
PUSH	Mem [0 + SP] <--- A,SP <--- SP + 1	Example	00 000 0010 --	----	SP	PC_out+1
POP	A <--- Mem [0 + SP - 1],SP <--- SP - 1	Example	Example	----	SP - 1	PC_out+1
NOP	NOP	Example	00 000 0010 --	----	----	PC_out+1
HALT	HALT	Example	00 000 0010 --	----	----	PC

Other instructions implementation

the follwoing instructions can be also implemented with the ones in IS:

• Call "function_name":

PUSH
SavePC
Push
Jmp "function address"
POP  

• Return:

POP
Add_A_Dir 4
LoadPC