I have an isr that is updating a display at a fixed frequency. I would like to tune my routine to minimize overhead and keep as much cpu time as possible open for other processing, but I don't have any good way to collect metrics to determine my cpu load.
I could look at the assembly and analyze the routine, but I don't have the patience or the ability to do that accurately. I don't feel like I need terribly fine grained results either, just a simple percentage of cpu time occupied by the isr.
I could set a pin high only when the isr is active and measure it externally. That has a minimum of overhead in the code, but I do not know what to measure it with. I don't have an oscilloscope or anything like that. Is there a simple ic or an easy way to use another micro to measure duty cycle? I have heard of dedicated frequency counter chips, but is there anything for duty cycle?