Jamie Lokier wrote:
>
> And if you can do that, you can probably make the custom CPU clear the
> flag _automatically_ on return-from-interrupt instructions :-)
Unfortunately the power of custom instructions is not that great with
NIOS2. With a MICO32 CPU that you implement in native HDL code and thus
can be modified in any way you want such nice things would be possible
(especially accessing memory from an additionally implemented
instruction), but the NIOS is closed source and hand-optimized by Altera
for the FPGA architecture (and thus I *hope* it is fast).
That is why custom instructions are restricted to resources offered by
the NIOS2 design (the two "read" registers given in the instruction.
I.e. the single "write" registers given in the instruction, bus
interface ("behind" the cache).
-Michael
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