>Somebody known anything about running NetBSD on Casiopea A-20A
>(ARM-based) ?

It will depend on which ARM cpu it uses.

>Old SH3-based A-20 also not supported, but it is not difficult to
>implement, because other mips-based Casiopea, such as E-105, are
>supported.

>Also, please, let me know about links, where I can find Casiopea A20
>hardware manuals and soon.

I couldn't even find basic sales information.

Where is it sold ?

Robert