[ECOS] Running ECOS on a SPARC with less than 8 register windows

[Mark Salter]

On Fri, 2005-03-04 at 15:42 +1100, Michael Cowell wrote:
> Hi,
> 
> I'm interested in using ECOS on a LEON2 SPARC processor running on an 
> FPGA development system. Using the LEON2 port of ECOS I have succeeded 
> in running all the tests in the source tree, and they all pass. However, 
> if I configure and synthesize my processor with less than 8 register 
> windows all of the tests fail. The function in which they fail varies 
> depending on the particular test, and sometimes the PC appears to be set 
> to garbage (i.e. outside of memory). Clearly the handler for the 
> register overrun trap does not expect a system with such a small number 
> of registers (am I wrong about this?).
> 
> The eventual application for the software is not the FPGA system, but an 
> embedded low power device, and the large register file required for 8 
> register windows is a significant problem.
> 
> Has anyone run ECOS on a SPARC with less than 8 register windows (the 
> SPARC architecture specification allows as little as 2)? Or, does anyone 
> know what I will have to modify in the HAL code to implement the correct 
> behavior in this situation?
> 

It looks like the code attempts to handle 6, 7 or 8 windows. I don't
know if the code has ever been run on CPUs with other than 8 windows.
Look for references to __WINSIZE in the hal/sparc code. There aren't
many places where __WINSIZE matters so it should be easy enough to
debug the existing code and add support for fewer windows.

--Mark



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