Soft microprocessor

Not to be confused with soft computing.

A soft microprocessor (also called softcore microprocessor or a soft processor) is a microprocessor core that can be wholly implemented using logic synthesis. It can be implemented via different semiconductor devices containing programmable logic (e.g., ASIC, FPGA, CPLD), including both high-end and commodity variations.

Most systems, if they use a soft processor at all, only use a single soft processor. However, a few designers tile as many soft cores onto an FPGA as will fit. In those multi-core systems, rarely used resources can be shared between all the cores in a cluster, leading to Jan's Razor.

Jan's Razor: In a chip multiprocessor design, strive to leave out all but the minimal kernel set of features from each processing element, so as to maximize processing elements per die.

—Jan Gray

While many people put exactly one soft microprocessor on a FPGA, a sufficiently large FPGA can hold two or more soft microprocessors, resulting in a multi-core processor. The number of soft processors on a single FPGA is only limited by the size of the FPGA. Some people have put dozens or hundreds of soft microprocessors on a single FPGA.

Core comparison

Processor	Developer	Open Source	Bus Support	Notes	Project Home
TSK3000A	Altium	No Royalty-Free	Wishbone	32-bit R3000 style RISC Modified Harvard Architecture CPU	Embedded Design on Altium Wiki
TSK51/52	Altium	No Royalty-Free	Wishbone / Intel 8051	8-bit Intel 8051 instruction set compatible, lower clock cycle alternative	Embedded Design on Altium Wiki
OpenSPARC T1	Sun	Yes		64-bit	OpenSPARC.net
MicroBlaze	Xilinx	No	PLB, OPB, FSL, LMB, AXI4		Xilinx MicroBlaze
PicoBlaze	Xilinx	Yes			Xilinx PicoBlaze
Nios, Nios II	Altera	No	Avalon		Altera Nios II
Cortex-M1	ARM	No			[6]
eSi-RISC	EnSilica	No	AMBA AXI, AHB and APB	Configurable as 16 or 32-bit. Supports ASIC and FPGA.	EnSilica eSi-RISC
LatticeMico32	Lattice	Yes	Wishbone		LatticeMico32
LEON2(-FT)	ESA	Yes	AMBA2	SPARC V8	ESA
LEON3/4	Aeroflex Gaisler	Yes	AMBA2	SPARC V8	Aeroflex Gaisler
Navré	Sébastien Bourdeauducq	Yes	Direct SRAM	Atmel AVR compatible 8-bit RISC	Project page at Opencores
OpenRISC	OpenCores	Yes	Wishbone	32-bit; Done in ASIC, Actel, Altera, Xilinx FPGA	OR1K
pAVR	Doru Cuturela	Yes		Atmel AVR compatible 8-bit RISC	Project page at Opencores
AEMB	Shawn Tan	Yes	Wishbone	MicroBlaze EDK 3.2 compatible Verilog core	AEMB
OpenFire	Virginia Tech CCM Lab	Yes	OPB, FSL	Binary compatible with the MicroBlaze	[7]
SecretBlaze	Lyonel Barthe	Yes	Wishbone	MicroBlaze ISA, VHDL	SecretBlaze
SYNPIC12	Miguel Angel Ajo Pelayo	Yes MIT		PIC12F compatible, program synthesised in gates	nbee.es
PacoBlaze	Pablo Bleyer	Yes		Compatible with the PicoBlaze processors	PacoBlaze
CPU86	HT-Lab	Yes		8088 compatible CPU in VHDL	cpu86
xr16	Jan Gray	No	XSOC abstract bus	16-bit RISC CPU + SoC featured in Circuit Cellar Magazine #116-118	XSOC/xr16
JOP	Martin Schoeberl	Yes	SimpCon / Wishbone (extension)	Stack oriented, hard real-time support, executes Java bytecode directly	Jop
ERIC5	Entner Electronics	No		9-bit RISC, very small size, C-programmable	ERIC5
YASEP	Yann Guidon	Yes AGPLv3	Direct SRAM	16 or 32 bits, VHDL & JavaScript, not ready, sort of anti-F-CPU	yasep.org (Firefox required)
Zet	Zeus Gómez Marmolejo	Yes	Wishbone	x86 PC clone	Zet
ZPU	Zylin AS	Yes	Wishbone	Stack based CPU, configurable 16/32 bit datapath, eCos support	Zylin CPU

See also

• SoC (System-on-a-chip)
• PSoC (Programmable System on a Chip)
• FPGA (Field-programmable gate array)
• Reconfigurable computing

External links

• Soft CPU Cores for FPGA
• Detailed Comparison of 12 Soft Microprocessors - broken link?
• FPGA CPU News
• Freedom CPU website (site damaged after the server was compromised)
• Microprocessor cores on Opencores.org (Expand the "Processor" tab)
• NikTech 32 bit RISC Microprocessor MANIK.