S2 Series


The SiFive S21 Standard Core is a full-featured 64-bit embedded processor based on the S2 Series. The S21 has separate Instruction and Data Buses, along with 2 banks of Tightly Integrated Memory (TIMs). The S21 is an ideal choice for area constrained applications demanding a 64-bit processor.

S21 Key Features

  • 64-bit AXI Ports
  • Machine and User Mode with 4 Region Physical Memory Protection
  • 3-stage pipeline with Simultaneous Instruction and Data Access
  • 2 Banks of Tightly Integrated Memory
  • CLIC interrupt controller with 127 interrupts
  • Advanced debug with 4 hardware breakpoints/watchpoints
  • 1.6 DMIPS/MHz
  • 3.2 Coremarks/MHz

No 64-bit Cortex Equivalent

S2 Series
Instruction Set Architecture
Dhrystone Performance
1.6 DMIPS/MHza
CoreMark Performance with GCC
3.2 CoreMarks/MHza
Floating-Point Unit
Memory Map
Up to 1024
Interrupt latency to C handler
Memory Protection Regions
Up to 8 (optional)
Tightly Integrated Memory
2 Banks of TIM (optional)

a. S21 Standard Core Configuration, using GCC

b. CLIC Vectored Mode

Series Overview

S2 Series

The S2 Series is a 64-bit microcontroller highly-optimized for area, efficient performance, and simplified integration into 64-bit SoCs. The S2 core has the same efficient 2‑stage or 3-stage pipeline as the E2 Series as well as a Core Local Interrupt Controller (CLIC) enabling extremely fast interrupt response. The S2 Series can be fully customized to meet your specific requirements.

S2 Series Highlights

Key Features

  • 64-bit CPU
  • Greater than 32-bit physical address
  • Optional Tightly Integrated Memory (TIM)
  • Configurability


  • 64-bit Embedded Controller
  • Consumer
  • Industrial Automation
  • Management Core

All Standard Cores

Standard Cores
ARM Comparison
E2 Series
M0, M0+, M3, M4, M23, M33
E3 Series
R4, R5
E7 Series
M7, R7, R8
S2 Series
S5 Series
R4, R5
S7 Series
M7, R7, R8
U5 Series
A5, A7, A35, A53
U7 Series