RTEMS 4.6.1 On-Line Library

CPU Initialization Initializing the CPU

RTEMS Porting Guide

4.3: Initializing the CPU

The _CPU_Initialize routine performs processor dependent initialization.

void _CPU_Initialize(
  rtems_cpu_table  *cpu_table,
  void            (*thread_dispatch)  /* may be ignored */
)

The thread_dispatch argument is the address of the entry point for the routine called at the end of an ISR once it has been decided a context switch is necessary. On some compilation systems it is difficult to call a high-level language routine from assembly. Providing the address of the _Thread_ISR_Dispatch routine allows the porter an easy way to obtain this critical address and thus provides an easy way to work around this limitation on these systems.

If you encounter this problem save the entry point in a CPU dependent variable as shown below:

_CPU_Thread_dispatch_pointer = thread_dispatch;

During the initialization of the context for tasks with floating point, the CPU dependent code is responsible for initializing the floating point context. If there is not an easy way to initialize the FP context during Context_Initialize, then it is usually easier to save an "uninitialized" FP context here and copy it to the task's during Context_Initialize. If this technique is used to initialize the FP contexts, then it is important to ensure that the state of the floating point unit is in a coherent, initialized state.

Finally, this routine is responsible for copying the application's CPU Table into a locally accessible and modifiable area. This is shown below:

_CPU_Table = *cpu_table;

RTEMS Porting Guide