The cross-development SDK for Sentinel 65X requires the Calypsi C/asm toolchain, targeting 65816. The SDK does not include Calypsi, which is available as freeware from [the Calypsi website](https://calypsi.cc).
Calypsi supports a fairly modern dialect of C, essentially C99 with some additions from later C standard revisions. The C standard library it supplies is used by the SDK, modified to work with the Sentinel 65X kernel installed to the on-board flash ROM.
Calypsi also provides a 65816 assembler, a linker, and a librarian, all of which are used by the SDK. Your SDK projects can be written in C, assembly language, or a mix of the two.
## Libraries
The SDK will include several useful libraries ready to use in your projects, under license terms which place no obligations on your own code's license terms.
