NVIDIA interview questions

Phone interview after applied online , and coding in a shared google doc about Verilog questions. They are medium level and maybe hard to solve without be able to show some of my drawings for the answer

HR set up the phone screen, A guy called me and used collabedit to ask me question about how to read a value from a running counter. I told him to use mutex to run the two threads mutually exclusive : one thread for updating(write) the counter and one thread for reading the counter. But he had no idea on how the mutex works. After the phone screen, I also emailed him a sample codes. He never replied.