With the growing popularity of edge computing and Internet of Things (IoT) devices, there is an increased need for secure computation on embedded devices. Typically, embedded devices have a heterogeneous environment and do not have general security protections compared to hosts on the cloud. As we see more third-party libraries and applications being run on embedded devices, we face the risk of system compromise that even the device's RTOS kernel cannot protect. There is a need for creating Trusted Execution Environments (TEEs) on embedded devices; however, many current TEEs have expensive hardware requirements. We propose using Keystone, a framework for creating customizable TEEs, on RISC-V architectures. The hardware requirement for creating TEEs in Keystone are generally available on standard RISC-V devices as RISC-V already provides PMP registers, the basis of Keystone's isolation. We propose using Keystone with FreeRTOS to implement a module in FreeRTOS for creating efficient and dynamic TEEs on embedded devices. We introduce ERTOS, a new module to FreeRTOS that allows the creation of secure tasks that can be attested and strongly isolated from other tasks using Keystone's security monitor. ERTOS exposes an easy-to-use API that allows developers to create and run enclave-protected tasks. ERTOS adds negligible performance overhead for computation-intensive tasks inside an enclave and introduces optimizations to allow inter-task communication to be more efficient.