Task configuration

This section is only concerning the asynchronous mode and it is only valid and applicable when asynchronous mode is enabled.

All the following configurations relate to the RTOS. For many OSs, the μC/DNSc task priority and stack sizes will need to be explicitly configured for the particular OS (consult the specific OS’s documentation for more information).

These configurations are defined in the dns-c_cfg.c file.

Task Configuration

µC/DNS use the following structure to configure his task.

Listing - µC/DNSc task Configuration Structure

typedef  struct  DNSc_cfg_task {
    CPU_INT32U   Prio;                                          /* Task priority.                                       */
    CPU_INT32U   StkSizeBytes;                                  /* Size of the stack.                                   */
    void        *StkPtr;                                        /* Pointer to base of the stack.                        */
} DNSc_CFG_TASK;

µC/DNSc stack has one internal task that needs to be configured. The task has its own DNSc_CFG_TASK object defining the task priority, the task's stack size and the pointer to start of task stack.

Task Priorities

We recommend you configure the Network Protocol Stack task priorities & Network application task priorities as follows:

Network TX De-allocation task (highest priority)
Network application tasks, such as DNSc instance.
Network timer task
Network RX task (lowest priority)

See Network Tasks Configuration for further information.

Task Stack Size

In general, the size of µC/DNSc task stacks is dependent on the CPU architecture and compiler used.

The only guaranteed method of determining the required task stack sizes is to calculate the maximum stack usage for each task. Obviously, the maximum stack usage for a task is the total stack usage along the task’s most-stack-greedy function path plus the (maximum) stack usage for interrupts. Note that the most-stack-greedy function path is not necessarily the longest or deepest function path.

The easiest and best method for calculating the maximum stack usage for any task/function should be performed statically by the compiler or by a static analysis tool since these can calculate function/task maximum stack usage based on the compiler’s actual code generation and optimization settings. So for optimal task stack configuration, we recommend to invest in a task stack calculator tool compatible with your build toolchain.

On ARM processors, experience has shown that configuring the task stacks to 1024 OS_STK entries (4,096 bytes) is sufficient for most applications. Certainly, the stack sizes may be examined and reduced accordingly once the run-time behavior of the device has been analyzed and additional stack space deemed to be unnecessary.

Task Stack Location and Allocation

If a specific memory location is desired for a task stack, the StkPtr parameter can be set to point to this specific memory segment. Else, if StkPtr is set to NULL, the task stack will be allocate on µC/LIB Heap.