80-24897-1 Rev. C QUALCOMM Proprietary 2-1
2 Overview of REX
REX is a preemptive, multitasking RTOS that provides APIs for task control, task synchronization, 1
mutual exclusion, timers, and interrupt control. All of its functions are executed in the context of the 2
calling task. 3
2.1 Tasks 4
REX treats tasks as independently handled entities, each having its own stack and priority that 5
collectively constitute the context of the task. Each task has an associated data structure, called a task 6
control block (TCB), which REX uses to keep track of the task’s context. 7
REX allows an arbitrary number of tasks to be created dynamically at any time during execution. 8
Realistically, however, REX’s performance degrades slightly with each added task since it must 9
traverse a longer list as more tasks are created. Care must be taken to keep the number of tasks to a 10
minimum. 11
Ultimately, the task load that REX can support is dependent upon the processor chosen, the processor 12
clock speed, and the interrupt characteristics of the particular system. 13
2.2 Stacks 14
As mentioned above, each task has its own stack that is active whenever the task is running. When a 15
task is suspended, its context is saved in a context frame on top of its stack, and the context frame’s 16
stack pointer is saved in the task’s TCB. An example of a suspended task is one that is blocked, 17
waiting for a signal, or waiting for an interrupt service. 18
When the task is again selected for running, the stack pointer is restored from the task’s TCB, the 19
task’s context frame is popped off its stack, and task execution resumes where it left off. The process 20
of task switching is virtually invisible to tasks. 21
22
我的内容管理
展开
