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This under-$6 SBC runs Linux on C-SKY ISA chip

Nov 13, 2018 — by Eric Brown 7,992 views

[Updated: 2PM] — Hangzhou C-SKY has launched a “C-SKY Linux Development Board” for $5.60 and up, featuring a 574MHz GX6605S CK610M SoC, 64MB DDR2 with a novel C-SKY ISA, plus an HDMI port, and 2x USB 2.0 ports.

Last month, Hangzhou C-SKY Microsystems Co. announced Linux 4.20~5.0 kernel support for its new C-SKY CK810 SoC design based on its new C-SKY ISA architecture. Now, Hangzhou C-SKY has launched a development board that runs Linux on a similar CK610M SoC. The C-SKY Linux Development Board sells for 39-40 Yuan ($5.60 to $7.05) on Taobao and $19.50 to $21.50 on AliExpress.

C-SKY Linux Development Board (left) and booting Linux
(click images to enlarge)

Hangzhou C-SKY is a member of the RISC-V Foundation, but its C-SKY ISA is independently developed. The GX6605S CK610M SoC, which is built by Hangzhou’s NationalChip unit, is aimed at low-end Linux IoT devices.

The CK610M model featured on the new dev board is the only CK610 model with an MMU, a key feature required to run Linux. The processor offers an 8-stage pipeline with dual-issue architecture, branch prediction, and speculative out-of-order execution.


The 574MHz clock suggests this is either a 40nm or 65nm fabricated model, which offer up to 700MHz or 666MHz performance, respectively, and provide dual 16KB caches. The CK610 features a DVB-S2/S demodulator, and as noted in the CNXSoft post that alerted us to the C-SKY Linux board, the chip has already appeared in several DVB-S2/S STBs available on Alibaba.

C-SKY Linux Development Board detail view (left) and CK610 SoC block diagram
(click images to enlarge)

The C-SKY Linux Development Board appears to be a bit smaller than a Raspberry Pi. Its onboard memory and storage are limited to 64MB DDR2 RAM and 4MB SPI flash for bootloader and media player code. More substantial storage will require the use of one of the two USB 2.0 host ports. There’s no Ethernet or wireless, so there goes the second USB port.

The SBC provides an HDMI port for up to HD resolution via H.264. Dual micro-USB ports support JTAG debugging and 5V/1A power with UART console, respectively. A 5-pin header offers 3.3V, GND, and 3x GPIO, and you get a reset button and several user buttons and LEDs. The Linux 4.16 based firmware uses buildroot with uClibc-NG.

Earlier C-SKY CK810 SoC design block diagram
(Source: Hangzhou C-SKY Microsystems via Phoronix)
(click image to enlarge)

A recent Phoronix. report on the C-SKY ISA’s new Linux kernel support quoted Linux kernel developer Arnd Bergmann saying that C-SKY might end up being the last new CPU architecture added to the kernel. Noted Phoronix: “He rightfully points out that most vendors now not part of the ARM/x86/POWER bandwagon are pursuing RISC-V based designs, which is already part of the mainline kernel…If any new CPU targets are added to the Linux kernel in the coming years, it’s likely to be some virtual target.”

Further information

The C-SKY Linux Development Board sells for 39-40 Yuan ($5.60 to $7.05) on Taobao and $19.50 to $21.50 on AliExpress under the somewhat misleading name “PK. OrangePi NanoPi Raspberry Pie!!! C-SKY Linux Development Board.” More information may be found on the C-SKY GitHub hardware and software pages. More on the C-SKY ISDA may be found at the C-SKY website.


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3 responses to “This under-$6 SBC runs Linux on C-SKY ISA chip”

  1. rwoodsmall says:

    This is not a RISC-V architecture SBC, it’s a custom chip design for set-top boxes/digital video delivery. and

  2. Lily says:

    C-SKY is not “RISC-V based” or “RISC-V derived”:

    “C-SKY is a member of the RISC-V Foundation but this architecture being added now is their own original design.”

  3. Jeff Child says:

    Lily, thanks for your comment. We have made the correction.
    – Jeff

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