shdl6800

This is a SpinalHDL reimplementation of Robert Baruch's 6800 processor implementation written in nMigen.

Robert also posts videos about the implementation, which you can find on his YouTube channel.

Why?

I am experimenting with several different hardware description languages, and nMigen (combined with the LiteX toolbox) looks really good. I also have some experience with SpinalHDL, and while watching his videos, it looked surprisingly similar to how you would implement it in SpinalHDL. This reimplementation is just to see how similar it can be to his implementation.

Status

• Part 3 is completed.
• Part 4 is completed.
• Part 5 is completed.
• Part 6 is completed.
• Part 7 is completed.
• Part 8 is completed.

The following instructions have been implemented:

• ADC (with formal add)
• ADD (with formal add)
• AND (with formal and)
• ASL (with formal sh_rot)
• ASR (with formal sh_rot)
• BCC (with formal br)
• BCS (with formal br)
• BEQ (with formal br)
• BGE (with formal br)
• BGT (with formal br)
• BHI (with formal br)
• BIT (with formal bit)
• BLE (with formal br)
• BLS (with formal br)
• BLT (with formal br)
• BMI (with formal br)
• BNE (with formal br)
• BPL (with formal br)
• BRA (with formal br)
• BSR (with formal br)
• BVC (with formal br)
• BVS (with formal br)
• CLC (with formal flag)
• CLI (with formal flag)
• CLR (with formal clr)
• CLV (with formal flag)
• CMP (with formal cmp)
• COM (with formal com)
• DEC (with formal inc_dec)
• DEX (with formal inc_dec_x)
• EOR (with formal eor)
• INC (with formal inc_dec)
• INX (with formal inc_dec_x)
• JMP (with formal jmp)
• LDA (with formal lda)
• LSR (with formal sh_rot)
• NEG (with formal neg)
• NOP
• ORA (with formal ora)
• ROL (with formal sh_rot)
• ROR (with formal sh_rot)
• SBC (with formal sub)
• SEC (with formal flag)
• SEI (with formal flag)
• SEV (with formal flag)
• STA (with formal sta)
• SUB (with formal sub)
• TAP (with formal tap)
• TPA (with formal tpa)
• TST (with formal tst)

Generating Verilog

Run the main function of the Core object:

sbt "runMain shdl6800.Core"

Running Simulation

To run simulation, you need Verilator. Once installed, run the main function of the Core object with sim as a parameter:

sbt "runMain shdl6800.Core sim"

This will generate Verilator code of the core and simulate the design as described in Core.scala. It will also generate a test.vcd trace file in the simWorkspace/Core folder, which you can view with GTKWave.

Formal Verification

Formal verification requires the free and open-source SymbiYosys and Boolector tools. Once installed, you can either formally verify all instructions, one by one:

make -s formal

Or verify them in parallel by specifying how many you want with the -j<number> flag. For example, to use all the cores of your CPU:

make -s formal -j$(nproc)

Or you can verify a single instruction by specifying the filename of the formal verification file of that instruction. For example, verifying the LDA instruction is done like this:

make -s Formal_LDA

License

shdl6800 is free and open hardware and is licensed under the ISC licence.