C-SKY ISA and SBCs -- requests for stories about obscure SoC dread

[Whales]

Heads up: I used to use an ARM laptop, so I'm no stranger to the fun that is running Linux on unpopular and non-mainline targeted devices.  I enjoy discovering what's out there, I'm not in it to buy them

C-Sky looks to be a a SoC + ISA that (based off my minimal research) is targeted for embedded video applications. 

What got me was a link to the C-SKY Linux project and the cheapness of an SBC running the platform (<10USD from taobao).  Gotta love the keyword spam.

Lots more info on the SBC, including links to manuals (Chinese) for the SoC and a list of specs.  Mostly low end:

• 64MB DDR2
• 574MHz
• "full USB 2.0" 
• Some flavour of proprietary graphics & video decoding by the looks of it.

What I'm really after are some nice, gruelling stories about anyone who has used these or heard stories about these; or any other obscure SoCs for that matter.  Bits of interesting technical info, tales of woe and documentation, anything .  "Obscure" can be defined however you like, even if it's a device that has sold in the millions.

[ataradov]

Linux-capable SoC in QFN package. This is interesting. Too bad all the documentation in Chinese.

Where is the documentation for the actual CPU core? Instruction set?

They seem to have also MCU-style cores and devices. But I wonder how much of an ARM-ripoffs they really are. Looking at some assembly code in the Linux port, it does not look like ARM at all.

[Whales]

Linux-capable SoC in QFN package. This is interesting. Too bad all the documentation in Chinese.

Good point.  Most of the stuff we have is BGA. 

Where is the documentation for the actual CPU core? Instruction set?

Both in the one doc: https://raw.githubusercontent.com/c-sky/tools/master/gx6605s/CK610_spec.pdf (search for MOV to get to the instructions) .  You will especially like the NDA notice at the bottom of each page.  Especially since the rest of the doc is in Chinese

[ataradov]

Both in the one doc:

That's some strange instruction set. It is like MIPS, but "extended" in a way that does not make a whole lot of sense, unless they tried to navigate patent minefield. At least it is unique.

Of course 200 page document can't be a complete documentation, but it is something, I guess.

I would really like to get the board, but dealing with Taobao is just frustrating.

You will especially like the NDA notice at the bottom of each page.  Especially since the rest of the doc is in Chinese

I looked on their site through google translator and they seem to have some documentation published, but it requires registration and my will power is not sufficient to do that

EDIT: Actually there are some interesting instructions: BGENI, BMASKI. Interesting use of a single "C" flag in some instructions. I'm not sure if that justifies actually adding that flag in a first place.

[abyrvalg]

Hehe, it was surprising to see BGENI, BMASKI words again after so many years This is Motorola M*CORE architecture. Checked the datasheet - encoding matches too. Only the instructions marked with "610E" and "620" are new. This arch was used in Motorola POG (Pot Of Gold) UMTS SoCs used in the first 3G Motorola phones (A835 etc). We even wrote an IDA Pro disasm module for it in those days. There were a gcc-style compiler by Diab and VRTX-MC RTOS port. Motorola was aiming at more dense (than ARM32) instruction encoding to cut the costs of NOR flashes.

[ataradov]

This is Motorola M*CORE architecture.

Cool. Now I have some reading to do. I've never heard of M*CORE.

It also looks like there is GCC port for M*CORE, so they really did not have to do much work.

Motorola was aiming at more dense (than ARM32) instruction encoding to cut the costs of NOR flashes.

I don't see how this is more dense. There are some nice instructions, but most of the immediate stuff has very short immediate values, making them sort of useless on their own.

EDIT: Ok, with all the Chinese stuff, I missed that instructions are 16-bit wide. This is an interesting instruction set then.

[abyrvalg]

After M*Core there was another obscure arch from the same company for the same field: StarCore. That was really crazy thing to disasm (a 4-unit VLIW arch).