CooCox CoOS User's Guide
CooCox CoOS User's Guide
CooCox CoOS User's Guide
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2.4 Task Ready List<br />
<strong>CooCox</strong> <strong>CoOS</strong> links all the TCB of ready tasks together according to the level<br />
of the priority through two-way linked list. This ensures that the first item of the<br />
list is always the one which has the highest priority and is the most in need of<br />
task scheduling.<br />
<strong>CooCox</strong> <strong>CoOS</strong> allows multiple tasks to share the same priority level.<br />
Therefore, tasks with the same priority will inevitably occur in the ready list.<br />
<strong>CooCox</strong> <strong>CoOS</strong> follows the principle "first-in-first out (FIFO)": put the latest task<br />
in the last of the tasks which share the same priority so that all of them can<br />
obtain its own CPU runtime.<br />
TCBRdy is the beginning of the ready list in <strong>CooCox</strong> <strong>CoOS</strong>. In other words,<br />
TCBRdy is the TCB of the task which has the highest priority in the ready list.<br />
Therefore, when starting a task scheduling, which only need to be checked is<br />
whether the priority of the task that TCBRdy pointed to is higher than the<br />
current running one. In this way, the efficiency of the task scheduling can be<br />
improved to the maximum.<br />
TCB 0(TCB Rdy) TCB 1 TCB 2 TCB n<br />
NULL<br />
TCBprev<br />
TCBprev<br />
TCBprev<br />
TCBprev<br />
TCBnext<br />
TCBnext<br />
TCBnext<br />
TCBnext<br />
NULL<br />
Figure 2.4.1 Task ready list<br />
15
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