Where to find addresses of registers?

file: ex.h

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How to light an LED?

int a=1; // cintrolling LED[0]
*LEDS_P = a;

or just

*LEDS_P = 1;

or if you want to preserve the other LEDs use

*LED_P |= 1;  // on
*LED_P &= ~1; // off

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How to write an interrupt handler?

void __attribute__ ((naked)) irq ()	// stack not used - FSM model
{}

or

void __attribute__((interrupt("IRQ"))) irq() // traditional return is possible
{}

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How to write a software exception handler?

void __attribute__ ((naked)) swi () // no return - FSM model
{}

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How to call the software exception?

void __attribute__ ((naked)) task (struct task_inst *d)
{...

  asm ("swi 0"); // SW exception to get back form User to Supervisor mode
}
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What are ARM modes, e.g. supervisor, IRQ, user, SWI, etc.?
Read ARM documents!!!

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How to specify tasks in your programme?

This is my example, which is compact, but you may have your own preferences...

struct task_inst
{
  void (*func) ();	// function pointer
  int run_phase, n, pwm_period, flash_half_period;	// parameters, can be separated for protection
  int flash_cnt, pwm_cnt, brightness, updown;	// static data
};

void task (struct task_inst *);
struct task_inst task_list[num_of_tasks] = {
  {task, 3, 0, 20, 500, 0, 0, 0, 0},
  {task, 3, 1, 20, 550, 0, 0, 0, 0},
  {task, 3, 2, 20, 600, 0, 0, 0, 0},
  {task, 3, 3, 20, 650, 0, 0, 0, 0},
  {task, 1, 4, 10, 350, 0, 0, 0, 0},
  {task, 1, 5, 10, 375, 0, 0, 0, 0},
  {task, 2, 6, 10, 400, 0, 0, 0, 0},
  {task, 2, 7, 10, 425, 0, 0, 0, 0}
};

void __attribute__ ((naked)) task (struct task_inst *d)
{...}

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How to implement the Sleep state?
The C compiler may eliminate "empty" loops if invoked with any optimisation options.
Use the following function to eliminate this possibility.
There are other more complicated options as well...

void __attribute__ ((naked)) sleep_state()
{
  asm ("sleep_forever: b sleep_forever");	// sleep, "asm" prevents loop elimination
}