how to control the mainloop interval?

[Suvcon]

I used to set a timer in MFC and make my render step with the TIMER Message,so I can control the interval of my app to swapbuffers,and it do well.

but I am now lost in glut.*&%^$^$%$#^%%$#$@#$
I only know the func glutMainLoop(void),but how can i control the loop interval by myself?

thank for your help or your notice me.