SYS/BIOS supports four different thread types. A thread is an independent execution object. SYS/BIOS is a preemptive, priority based schedule – the highest priority thread that is ready to run, will always run. The Idle thread manages background processing. This is the lowest priority thread which means that it only runs when no other threads are ready to run. TI provides some bookkeeping functions in the idle loop, such as checking to make sure that stacks have not overflowed and calculation of the CPU load. The longer time user spends in the idle loop, the lower the CPU load. For deployed systems, where this bookkeeping does not make sense, it is possible to plug a CPU low-power instruction in the idle loop to put the CPU in low power mode until the next interrupt. Tasks require a separate stack and allow an application to be logically split up according to function and sub-system. They allow multiple developers to work on different parts of the system and then integrate later. TI supports multiple task priorities. Software interrupts provide a slightly lower priority of processing than traditional ISRs. ISRs can defer less important processing to a SWI. This can be used to keep HWI interrupt time to a minimum. Finally, the highest priority threads are hardware interrupt threads or ISRs. Hardware interrupts and software interrupts both execute on the common system stack.