Semiconductor device, diagnostic test, and diagnostic test circuit

A semiconductor device comprising:

• a system bus;
• a plurality of Central Processing Unit (CPU) cores each connected to the system bus, comprising at least a scan chain for each of the plurality of CPU cores, and being assigned one or more tasks and configured to perform one of the tasks in a normal operation state;
• and
• a diagnostic test circuit connected to the system bus and capable of communicating with the plurality of the CPU cores, and configured to perform a scan test for the plurality of the CPU cores by using the scan chains, wherein
• any of the plurality of the CPU cores outputs a test start instruction signal to the diagnostic test circuit,
• when the test start instruction signal is output from any one of the plurality of the CPU cores, the diagnostic test circuit performs a scan test for the one of the plurality of the CPU cores in accordance with the test start instruction signal.