Computer Organization with Logisim

Logisim designs for teaching computer organization.

© 2021 Mehmet Kayaalp.

Cite as:

Mehmet Kayaalp. 2021. Using Logisim-evolution for Teaching Datapath and Control. In Proceedings of WCAE ’21: Workshop on Computer Architecture Education (WCAE ’21). ACM, New York, NY, USA, 8 pages.

See mkayaalp.net/computer-organization-logisim for details.

The circuit files in this repository:

• Logic design review examples
  • Combinational circuit example (full adder): full_adder.circ
  • Sequential circuit example: sequential.circ
  • Synchronous circuit example (four-bit T flip-flop counter: sync.circ
  • Propagation delay example (five-bit D flip-flop counter: propagation.circ
  • Tristate buffer and multiplexer example: tristate_mux.circ
  • 4-to-1 multiplexer: mux4.circ
• Combinational vs. pipelined multiplier
  • Combinational 3-bit multiplier: combinational_multiplier.circ
  • Pipelined 3-bit multiplier: pipelined_multiplier.circ
• Incrementally building a Stored Program computer
  • 3-bit accumulator machine: acc3.circ
  • 4-bit accumulator machine: acc4.circ
  • Simplified 4-bit accumulator machine: acc4_simplified.circ
  • 4-bit accumulator machine with 4 registers: acc4_4regs.circ
  • 4-bit register (3-operand) machine with 4 registers: reg4_4regs.circ
  • Added an instruction register: ins_register.circ
  • Added an instruction memory: ins_memory.circ
  • Added a branch instruction: branch.circ
  • Added a conditional branch instruction: conditional_branch.circ
  • Added a load (from data memory) instruction: load_data_memory.circ
  • Added a store (into data memory) instruction: store_data_memory.circ
• Converting the design into ARMv8
  • Increase register width to 64-bits: 1_use64bitregs.circ
  • Increase the number of registers to 8: 2_use8regs.circ
  • Increase the number of registers to 16: 3_use16regs.circ
  • Increase the number of registers to 32: 4_use32regs.circ
  • Put registers into a Register File subcircuit: 5_useregfile.circ
  • Increase instruction size to 32-bits: 6_use32bitinstructions.circ
  • Use byte-addressed instruction memory: 7_usebyteaddressedinsmem.circ
  • Use the ARMv8 instruction encoding format: 8_usearmv8instructionformat.circ
  • Add the sub (register) instruction: 9_implement_sub.circ
  • Add the sub (immediate) instruction: 10_implement_sub_imm.circ
  • Fix the offset for ldur and stur: 11_fixldursturoffset.circ
• Physical lab
  • LED Blink circuit: led_blink.circ
    • Improved ARMv8 datapath with subcircuits
    • Added LED outputs and subcircuit layouts for easy debugging
    • Added instructions: bl, cbnz, ldur (word), stur (word), lsl, lsr
    • Added PC resetting to 0080_0000 (the program starting address for Raspberry Pi 3)
    • Added a memory controller with peripheral addresses starting at 3F00_0000 (matching Raspberry Pi 3)
    • Added a GPIO peripheral at address 3F20_0000 (matching BCM2837 of Raspberry Pi 3)
    • Added BCM2837 GPIO registers: GPFSELn, GPSETn, GPCLRn
  • Datapath improvements: added_sp_br_flags_adds_subs_ands_bcond.circ
    • Added proper handling of SP register
    • Added flags register used in conditional branching
    • Added flag-setting variants: adds, subs, ands
    • Added indirect branch instruction: br
    • Added flag-based conditional branch instructions: b.cond
  • More instructions: added_imms_mul_div_accesssize_varshift.circ
    • Added logical immediate encoding
    • Added wide-immediate instructions: movz, movk, movn
    • Added variable logical shift: lslv, lsrv
    • Added multiplication and division: mul, umulh, smulh, udiv, sdiv
    • Added half-word- and byte-sized memory access: ldurh, sturh, ldurb, sturb
  • LCD display: added_lcd_display.circ
    • Added PC-relative address instruction: adr
    • Added an I2C peripheral (send-only) at address 3F80_4000 (matching BSC1 of BCM2837 of Raspberry Pi 3)
    • Added BCM2837 BSC registers: C, S, DLEN, ADDR, FIFO_DATA
    • Added an I2C device (receive-only) (matching the PCF8574 on the LCD backpack)
    • Added an HD44780 module with a character matrix LCD display
• Pipelined LEGv8 datapath with forwarding unit (no hazard detection or stalling): pipeline.circ