As @fanoush says really - Inline C (http://www.espruino.com/InlineC) should 'just work' for you (with the existing, online compiler if you're using official boards). In fact I believe you could do inline assembler inside the Inline C, which should actually work pretty nicely.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
As @fanoush says really - Inline C (http://www.espruino.com/InlineC) should 'just work' for you (with the existing, online compiler if you're using official boards). In fact I believe you could do inline assembler inside the Inline C, which should actually work pretty nicely.