Sifive Essential 6-Series RISC-V processors target Linux, real-time applications


SiFive has been busy. Just days after the announcement of SiFive Performance P650, the company announced the SiFive Essential 6-Series RISC-V processor family starting with four 64-bit / 32-bit real-time cores and two Linux-compatible application cores, plus the SiFive Version 21G3 with various improvements to existing families.

SiFive Essential 6-Series line of RISC-V processors

The Essential 6-Seris family is made up of three sub-families with two processors each:

  • E6 Series with 1.91 DMIPS / MHz, 3.69 CoreMark / MHz
    • E61-MC – 32-bit quad-core onboard processor
    • E61 – Mid-range performance 32-bit on-board processor (one core)
  • S6 series with 2.07 DMIPS / MHz, 3.73 CoreMark / MHz
    • S61-MC – 64-bit quad-core onboard processor
    • S61 – Mid-range performance 64-bit embedded processor (one core)
  • U6 Series with 2.07 DMIPS / MHz, 3.73 CoreMark / MHz
    • U64-MC – Quad-Core 64-Bit Application Processor
    • U64 – Linux-compatible midrange processor (one core)

The E6 and S6 series real-time processors have virtually the same specifications, except for 32-bit and 64-bit cores, and a different number of interrupts.

  • Fully compliant with the RISC-V ISA specification
    • Up to four 32-bit RV32Is (E6 series) or 64-bit RV64I (S6 series) RISC-V kernels
    • Machine and user mode support
    • 8-step pipeline, unique number and in order
  • Advanced memory subsystem
    • 16 KB, bidirectional instruction cache
    • Tight Integrated Instruction Memory (ITIM) option
    • Up to 64KB Data Tightly Integrated Memory (DTIM) support
  • Efficient and flexible interruptions
    • Local interrupts with vectorized addresses – up to 16
    • Platform Level Interrupt Controller (PLIC)
      • E6 series – 128 interrupts with 7 priority levels
      • S6 series – 511 interrupts with 7 priority levels
    • RISC-V main local switch (CLINT) – 1 timer, 1 software
  • 8-region physical memory protection (PMP)
  • High performance AMBA interfaces
  • Detailed Power, Performance and Area (PPA) Info – SiFive will only tell you by email …

SiFive U6

Highlights of the U6 series application processors:

  • Fully compliant with the RISC-V ISA specification
  • Up to four 64-bit RISC-V application cores
    • 32KB I-cache L1 with ECC
    • 32 KB L1 D-cache with ECC
    • 8-region physical memory protection
    • Support for virtual memory with up to 47 physical address bits
    • 128KB L2 cache integrated with ECC
  • Real-time capabilities
    • L2 cache can be configured in deterministic high speed SRAMs
  • CLINT for multicore timer and software interrupts
  • PLIC with support for up to 128 interrupts with 7 priority levels – Debugging with instruction trace
  • Detailed Power, Performance and Area (PPA) information – Again, no luck unless you contact SiFive directly

The Essential 6-Series is essentially the mid-range equivalent of the high-end SiFive 7 Series processors. Further details can be found on the SiFive Essential page.

SiFive RISC-V vs. Arm Cortex

SiFive says the E6 series is equivalent to the Arm Cortex-M0, M0 +, M3, M4, M23, and M33 cores, a fairly wide range, but they haven’t listed any Arm Cortex equivalent for the S6 and U6 series.

SiFive 21G3 version

In addition to the new RISC-V cores, SiFive also announced version 21G3 with improved clock synchronization and power management, SiFive Shield WorldGuard support for the Essential family, and the SiFive Performance family now includes RISC-V Hypervisor extension, as discussed in the recent Performance P650 kernel announcement. SiFive Intelligence Extensions found in SiFive Intelligence X280, add support for BFLOAT16 compute, quantization acceleration and get better multi-cluster support to improve performance of learning workloads Automatique.

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