Microprocessor apparatus for secure on-die real-time clock

A microprocessor apparatus, for executing secure code within a secure execution environment, the microprocessor apparatus comprising:

• a secure non-volatile memory, configured to store a secure application program;
• a microprocessor, coupled to said secure non-volatile memory via a private bus, configured to execute non-secure application programs and said secure application program, said microprocessor comprising:
• a secure real time clock, configured to provide a persistent time, wherein said secure real time clock is only visible and accessible by said secure application program when said microprocessor is executing in a secure mode;
• and
• an external crystal, coupled to said secure real time clock within said microprocessor, configured to cause an oscillator within said secure real time clock to generate an oscillating output voltage that is proportional to the frequency of said external crystal.

A method for executing secure code within a secure execution environment, the method comprising:

• fetching the secure code from a secure non-volatile memory over a private bus for execution by a microprocessor that is coupled to the secure non-volatile memory, wherein the private bus is isolated from all system bus resources within the microprocessor and external to the microprocessor, and wherein the private bus is observable and accessible exclusively by secure execution logic within the microprocessor;
• via a secure real time clock within the microprocessor, providing a persistent time, wherein the secure real time clock is only visible and accessible by the secure code;
• and
• coupling an external crystal to the microprocessor that causes an oscillator within the real time clock to generate an oscillating output voltage that is proportional to the frequency of the external crystal.