I have searched on the internet on how to get Euler angels from IMU measurements,I found that kalman filter and mahony filter are used...kalman filter has a drawback of complex computations,but mahony has less computation,so mahony is preferred for 8 bit microcontroller,but accuracy of kalman is better than mahony,so my question is ,can we implement kalman filter with its complex computations on 8 bit microcontroller like atmega32
Sure, it can be done, and simply enough. Here is an implementation in C that could be easily adapted.
It won't be as fast as Mahoney, of course, but the calculations are possible. The question is, is it fast enough for your usage?