Error (12007): Top-level design entity "jishu" is undefined

This error indicates that the top-level design entity named "jishu" has not been defined or declared in the Verilog code. The compiler cannot recognize the module or entity named "jishu" and hence cannot proceed with the synthesis process.

To resolve this error, you need to make sure that the top-level design entity is properly defined and declared in your Verilog code. Check the module declaration and make sure that the module name matches with the top-level entity name. Also, check if all the required inputs and outputs are defined and declared properly.

Make sure that you have not misspelled the name of the module or entity. Also, make sure that the Verilog file containing the top-level entity is included in the project or compilation unit.

Once you have made the necessary corrections, try recompiling the code to see if the error has been resolved.