Sharing and protecting secured subordinate devices on an unsecured bus

Abstract

A peripheral controller includes a serial engine configured to provide an interface to a serial bus, a multiplexer configured to select between transactions directed to the serial bus and initiated in a plurality of execution environments, and an access control circuit configured to determine when a first transaction to be executed over the serial bus is initiated from a first execution environment, enforce an access policy when the first execution environment is a secured execution environment, determine when a second transaction is initiated from a second execution environment, block the second execution environment and a peripheral device from accessing the serial bus when the first execution environment is accessing the serial bus, and provide the second execution environment and the peripheral device access to the serial bus when the second execution environment is an unsecured execution environment. The access policy may be based on an address of a peripheral device.