Installing or upgrading cygwin for nios2 5.0

I have my own install of cygwin in C:/cygwin that I keep separate from my Quartus/Nios cygwin(s).

Unfortunately, the nios_bash scripts and their ilk in Quartus/Nios are rather scorched-earth, overwriting your PATH variable and such, so I haven't found a simple way for my cygwin environs to pull in everything from Altera without breaking things.

That said, it isn't hard, on a case-by-case basis, to add those things you need (paths and such) to your own cygwin environment. There are a couple of SOPC-related environment variables added to the Windows environment, so all the cygwins will pick them up.

Also, keeping your own cygwin separate prevents problems with incompatible versions, and there is no need to reinstall everything when you get a new Quartus or Nios2.