sbmips

Naïve MIPS32-like CPU design on a Xilinx FPGA

Features

• Five-stage pipeline

• Data forwarding

• One-instruction delay slot

• No branch prediction

• No privileged instructions

• No interruptions or exceptions

Academic reference purpose only, contains bugs, not suitable for production.

Implemented instructions

R-Type

• sll - Logical left shift
• srl - Logical right shift
• sra - Arithmetical right shift
• sllv - Logical left shift by value
• srlv - Logical right shift by value
• srav - Arithmetical right shift by value
• jr - Jump by register
• jalr - Jump and link by register
• add - Add
• addu - Add without overflow check
• sub - Subtract
• subu - Subtract without overflow check
• and - Bitwise and
• or - Bitwise or
• xor - Bitwise exclusive or
• nor - Bitwise not or
• slt - Set if less than
• sltu - Set if unsigned less than

I-Type

• beq - Branch if equal
• bne - Branch if not equal
• addi - Add immediate value
• addiu - Add immediate value without overflow check
• slti - Set if less than immediate value
• sltiu - Set if less than unsigned immediate value
• andi - Bitwise and immediate value
• ori - Bitwise or immediate value
• xori - Bitwise exclusive or immediate value
• lui - Load immediate value as upper half-word
• lw - Load word from memory
• sw - Store word from memory

J-Type

• j - Jump
• jal - Jump and link

Available pseudo-instructions

• la - Load address
• li - Load immediate value
• move - Move register
• negu - Negation
• nop - No operation
• not - Bitwise not
• b - Branch
• bal - Branch and link
• beqz - Branch if equal to zero
• bnez - Branch if not equal to zero

Model

Development board: Digilent Nexys 3

FPGA chip: Xilinx Spartan-6 xc6slx16-3csg324

I/O

• clk (btn) and rst are controlled by two buttons, so you can single-step over the program.

• gclk is driven by 100 MHz quartz crystal resonator.

• led_sel is bond to 8 switches.

• led powers the 4-digit seven-segmented display, showing values of different registers according to led_sel.

License

Released under GNU General Public License version 3 (GPLv3).

See LICENSE for more information.