ioannisin/tt03-hovalaag

HOVALAAG CPU for Tiny Tapeout 03

HOVALAAG CPU for Tiny Tapeout

HOVALAAG (Hand-Optimizing VLIW Assembly Language as a Game) is a free Zachlike game.

HovalaagCPU is my Verilog implementation of the CPU from the game. This is a project to implement it on Tiny Tapeout.

Thank you to @nothings for the fun game, making the assembler public domain, and for permission to create this hardware implementation.

Implementation details

The processor is described in detail on the game pages. Here we will document the wrapper to allow it to be used through Tiny Tapeout.

The processor uses 32-bit instructions and has 12-bit I/O. Tiny Tapeout effectively has 6 bits input and 8 bits output per clock (because 2 input bits are required for clock and reset).

The instruction and data therefore need to be passed in and out over several (currently 10) clocks per processor clock. The cycle is as follows:

Clock	Input 7-2	Output
0	Instruction 5-0	Register A for debug
1	Instruction 11-6	Register B for debug
2	Instruction 17-12	Register C for debug
3	Instruction 23-18	Register D for debug
4	Instruction 29-24	Register W for debug
5	Instruction 31-30	IO update indication
6	New IN1 5-0	New PC
7	New IN1 11-6	OUT 5-0, high, clock
8	New IN2 5-0	OUT 11-6, high, clock
9	New IN2 11-6	OUT 3-0 for 7 segment display

The OUT values written at stages 7 and 8 are formatted suitably for input directly into my FIFO module.

The IO update indication bits on the 6th clock are as follows:

Bit	Meaning
0	Advance IN1
1	Advance IN2
2	Write OUT to OUT1
3	Write OUT to OUT2

The implemented design also adds the following ALU ops in the unused range (originally documented as BCD conversions, but previously never used):

1101   A
1110   Random number
1111   The constant 1

TODO

Physical testing - would be good to try this on an FPGA or Verilog compiled for Pico and check interfacing with it works as expected.

Not doing because we've run out of space:

• Option to format debug for 7 segment (set option using another IO when reset_en high)

Making the hardware usable:

• Modified version of the assembler supporting the new ops.
• Easy way to assemble a vasm program and build the output plus some data into a firmware for Pico
• Firmware for Pico to communicate with the PCB. Ideally could be generally useful for any design.

What is Tiny Tapeout?

TinyTapeout is an educational project that aims to make it easier and cheaper than ever to get your digital designs manufactured on a real chip!

Go to https://tinytapeout.com for instructions!

How to change the Wokwi project

Edit the info.yaml and change the wokwi_id to match your project.

How to enable the GitHub actions to build the ASIC files

Please see the instructions for:

• Enabling GitHub Actions
• Enabling GitHub Pages

How does it work?

When you edit the info.yaml to choose a different ID, the GitHub Action will fetch the digital netlist of your design from Wokwi.

After that, the action uses the open source ASIC tool called OpenLane to build the files needed to fabricate an ASIC.

Resources

• FAQ
• Digital design lessons
• Learn how semiconductors work
• Join the community

What next?

• Share your GDS on Twitter, tag it #tinytapeout and link me!