842 schoolRISCV CPU with Fibonacci program :: Quicker, easier and cheaper to make your own chip!

How it works

A minimalistic SoC with a schoolRISCV educational CPU and a ROM memory with a program that computes the Fibonacci numbers.

schoolRISCV was originally designed by Stanislav Zhelnio and Alexander Romanov (HSE MIEM) by a suggestion from Yuri Panchul. The goal was to create the simplest possible CPU suitable for the introductory Verilog and FPGA classes. The design was based on a textbook Digital Design and Computer Architecture by David Harris and Sarah Harris. Later on Yuri Panchul and Mike Kuskov (Innopolis) adopted the design for the GitHub repositories systemverilog-homework and basics-graphics-music. Now these repos are maintained by the engineers and educators associated with the Verilog Meetup community.

How to test

SystemVerilog testbench

A self-checking testbench for the design is located in a directory test_extra that contains:

clean.bash - a script to delete temporary files produced by simulate.bash.
simulate.bash - a script that simulates the design together with a testbench using Icarus Verilog, producing log.txt. Before the simulation, the script compiles assembly program.s using the RARS instruction set simulator (ISS) that generates a file program.hex. This program.hex is used to fill the ROM for both simulation and synthesis.
tb.sv - a self-checking testbench that generates a log and the status PASS or FAIL.

cocotb testbench

The cocotb testbench just runs the simulation for 300 clock cycles checking that the value of the lowest two bits of the dedicated outputs uo_out is equal to 01 at the end, which corresponds to self-diagnostics PASS and not FAIL.

Post silicon

After the manufacturing, the design can be manually tested by resetting, driving a clock, and observing the outputs. If the LED connected to the bit 0 of the dedicated outputs (uo_out) turns on (PASS) and the LED connected to bit 1 turns off (FAIL) the design probably works.

Furthermore, you can drive a slow 3 Hz clock and observe the LEDs connected to the bidirectional signals uio_out. Those pins are configured as outputs and they output the lowest 4 bits of the CPU program counter (PC) and the lowest 4 bits of the RISC_V architecture register a0 (register 10) that contains the currently computed Fibonacci number.

External hardware

LEDs.

#	Output	Bidirectional
0	Test pass	CPU reg a0[0]
1	Test fail	a0[1]
2		a0[2]
3		a0[3]
4		Program Counter pc[0]
5		pc[1]
6		pc[2]
7		pc[3]

842 schoolRISCV CPU with Fibonacci program