[J-core] qemu support

[Rich Felker]

On Tue, Apr 26, 2016 at 08:15:58AM -0400, Christopher Friedt wrote:
> Hi List,
> 
> just out of curiosity, has anyone started working on Qemu support for
> j2 and e.g. the Numato board?

No. It's something on my medium to long term agenda, but if somebody
else wants to try sooner that would be great. I think it would make
sense to start by converting qemu's sh support over to taking as input
a device tree for the hardware to emulate rather than hard-coding a
fixed board, but you could get by without this step.

The minimal change needed to run j2/sh2 bare-metal/kernel code (vs sh4
code) is that the trap/interrupt mechanism has to jump to _code_ in
the trap vector table rather than loading an address from the table.
Aside from that, support for the j2 cas.l (compare and swap)
instruction should be added, and instructions not available on j2
(i.e. all insns new on sh3+ except the barrel shifter) should be made
to trap so that code that can't actually run on the real hardware gets
caught.

Rich