abstractaccelerator/uriscv

uriscv - Another tiny RISC-V implementation

Github: https://github.com/ultraembedded/core_uriscv

Simple, small, multi-cycle 32-bit RISC-V CPU implementation.
Most instructions take 2 cycles, apart from load/stores which take 4+ cycles (depending on memory latency), and division which can take up-to 34 cycles.

Features

• 32-bit RISC-V ISA CPU core.
• Support RISC-V’s integer (I), multiplication and division (M), and CSR instructions (Z) extensions (RV32IMZicsr).
• Implements base ISA spec v2.1 and parts of the privileged ISA spec v1.11.
• Supports machine mode privilege level only.
• Configurable support for exceptions, interrupts, timers, multiplication, division and error traps.
• Verified using random instruction sequences using cosimulation against C++ ISA model.
• Synthesizable Verilog 2001, Verilator and FPGA friendly.
• Coremark: 1.48 CoreMark/MHz (with HW mul/div)
• Dhrystone: 0.58 DMIPS/MHz ('legal compile options' / 337 instructions per iteration / with HW mul/div)

For my higher performance pipelined cores, see here:

• Coremark: 2.94CM/MHZ - http://github.com/ultraembedded/riscv
• Coremark: 4.1CM/MHz - http://github.com/ultraembedded/biriscv

Getting Started

Running Helloworld

To run a simple test image on the core RTL using Icarus Verilog;

# Install Icarus Verilog (Debian / Ubuntu / Linux Mint)
sudo apt-get install iverilog

# [or] Install Icarus Verilog (Redhat / Centos)
#sudo yum install iverilog

# Run a simple test image (test.elf)
cd demo
make

The expected output is;

Starting bench
VCD info: dumpfile waveform.vcd opened for output.

Test:
1. Initialised data
2. Multiply
3. Divide
4. Shift left
5. Shift right
6. Shift right arithmetic
7. Signed comparision
8. Word access
9. Byte access
10. Comparision

Configuration

Param Name	Valid Range	Description
SUPPORT_MUL	1/0	Enable multiplication instructions.
SUPPORT_DIV	1/0	Enable division instructions.
SUPPORT_CSR	1/0	Global enable for CSR/trap/interrupt handling.
SUPPORT_TRAP_LSU_ALIGN	1/0	Enable unaligned memory load / store exception.
SUPPORT_MTVEC	1/0	Configurable exception entry address.
SUPPORT_MTVAL	1/0	Support MTVAL CSR (holds bad addr / opcode).
SUPPORT_MIP_MIE	1/0	Support MIE and MIP CSR registers.
SUPPORT_MSCRATCH	1/0	Support MSCRATCH CSR registers (SW read/write).
SUPPORT_MCYCLE	1/0	Support cycle counter / rdtime.
SUPPORT_MTIMECMP	1/0	Non-std - support timer compare interrupt.
SUPPORT_TRAP_INVALID_OPC	1/0	Fault on invalid opcodes (enable SW emulation).
SUPPORT_BRAM_REGFILE	1/0	FPGA BlockRAM friendly reg file (inst take 1 cycle longer).
ISR_VECTOR	'h0-FFFFFFFF	ISR addr = reset_vector + ISR_VECTOR (SUPPORT_MTVEC = 0).