minimax
ZPUFlex
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minimax | ZPUFlex | |
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13 | 1 | |
194 | 34 | |
- | - | |
2.9 | 10.0 | |
8 days ago | over 8 years ago | |
Verilog | VHDL | |
BSD 3-clause "New" or "Revised" License | - |
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minimax
- Is the 6502 a RISC or CISC processor? (2005)
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A Single-Cycle 64-Bit RISC-V Register File
On FPGAs, a register file probably fits better into distributed RAM than block RAM.
On Xilinx, for example: a 64-bit register file doesn't map efficiently to Xilinx's RAMB36 primitives. You'd need 2 RAMB36 primitives to provide a 64-bit wide memory with 1 write port and 2 read ports, each addressed separately. Only 6% (32 of 512) entries in each RAMB36 are ever addressable. It's this inefficient because ports, not memory cells, are the contented resource and BRAMs geometries aren't that elastic.
A 64-bit register file in distributed RAM, conversely, is a something like an array of DPRAM32 primitives (see, for example, UG474). Each register would still be stored multiple times to provide additional ports, but depending on the fabric, there's less (or no) unaddressed storage cells.
The Minimax RISC-V CPU (https://github.com/gsmecher/minimax; advertisement warning: my project) is what you get if you chase efficient mapping of FPGA memory primitives (both register-file and RAM) to a logical conclusion. Whether this is actually worth hyper-optimizing really depends on the application. Usually, it's not.
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Verilator - Do I need to maintain two testbench suits?
I haven't used it on a huge design (I'm usually a VHDL person), but it was a hassle-free replacement for iverilog when regression testing Minimax. Performance is substantially better; compilation times are worse.
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Zylin ZPU: The worlds smallest 32 bit CPU with GCC toolchain
Note that you can't compare LUT4 results (ZPU @ 440 LUTs) against LUT6 results (PicoRV32 @ 750 LUTs). The ZPU is remarkably small, and it's a bigger gap than a direct comparison shows.
SERV is a fair comparison, since it's architected for 4LUTs and I suspect the synthesis results come from iCE40 tools.
I have a contender in the "very small" space, too [1], although I don't claim it's as mature or complete as SERV. (If Minimax was excluded from your post on the basis of insanity, I'm OK with that.)
[1] https://github.com/gsmecher/minimax
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Senior Design Project Ideas?
I develop Minimax (https://github.com/gsmecher/minimax), an open-source RISC-V implementation. It's currently written in both VHDL and Verilog (the two implementations are equivalent, though I am likely to drop the VHDL implementation if it's too much work to keep them both.)
- Compiled and Interpreted Languages: Two Ways of Saying Tomato
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PicoBlaze in Verilog / Vivado
The best point-of-entry for "tiny" MCUs these days is FemtoRV32-Quark or SERV. I also maintain my own small RISC-V core (Minimax), though it's early on in graduating from "experiment" to "real design".
- Show HN: Minimax – A Compressed-First, Microcoded RISC-V CPU
- Minimax: A Compressed-First, Microcoded RISC-V CPU
ZPUFlex
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Zylin ZPU: The worlds smallest 32 bit CPU with GCC toolchain
For me the most interesting thing about ZPU is that its instructions are only a single byte each, which means that while the CPU is much smaller than most RISC-V implementations, the code density is significantly better than RV32 code. (Compressed RISC-V code can beat ZPU, but adding the compressed instruction set to a RISC-V core increases its size quite a bit.)
I did play with the ZPU quite a bit 8 or 9 years ago, and forked the ZPU Small variant to create ZPUFlex [0]. I borrowed a number of ideas from ZPU when I created my own CPU Project, EightThirtyTwo [1], some years later.
[0] https://github.com/robinsonb5/ZPUFlex
What are some alternatives?
picorv32 - PicoRV32 - A Size-Optimized RISC-V CPU
zpu - The Zylin ZPU
Artix-7-HDMI-processing - Receiving and processing 1080p HDMI audio and video on the Artix 7 FPGA
EightThirtyTwo - An experimental CPU core with 8-bit instruction words and 32-bit registers
sulong - Obsolete repository. Moved to oracle/graal.
pinwheel - A tiny RISC-V processor for hard-real-time FPGA-based applications.
serv - SERV - The SErial RISC-V CPU
zpugcc
riscof
mini-rv32ima - A tiny C header-only risc-v emulator.
ch32v003 - CH32V003 is an ultra-cheap RISC-V MCU with 2KB SRAM, 16KB flash, and up to 18 GPIOs that sells for under $0.10