Dear Friend, I am not sure if it is a bug.when i simulate this core with the tool modelsim,the testbench will stop at some time and show:

status: 21600 generate 'start', write cmd 20 (slave address+write)

so the follow code could not run,i don't know why,thank you for your reply :)

This is not a bug, please only report issues with the core (or the testbench) as bugs. Not tool issues. I ran the testbench with ncsim and modelsim. Both work/pass.

In zhe code , I found that zhe signal sda_o is always set to '0'. WHY?