Help in CRC custom instructions please.

I don't think there is any simpler example available from Altera. But basically you need to read the www.altera.com/literature/manual/mnl_avalon_spec.pdf]avalon (http:[url) specification[/url], mostly the part about the memory mapped slave interface. Then you can create your component with such an interface, and use the component creator in SOPC Builder or QSys to make the .tcl file for you.

You don't actually need to create a sw.tcl file in most cases, but you will need to write some C to access your component. The IORD and IOWR macros can be used to read or write the different registers.

There shouldn't be anything preventing you from using the example checksum component in a DE1 project with Nios II EDS, it should work just as is.