#include "systick.h"

#include "ch32v003fun.h"

// Global variable definition
volatile uint32_t systick_millis;

/*
 * Initialises the SysTick to trigger an IRQ with auto-reload, using HCLK/1 as
 * its clock source
 */
void systick_init(void) {
  // Reset any pre-existing configuration
  SysTick->CTLR = 0x0000;

  // Set the compare register to trigger once per millisecond
  SysTick->CMP = SYSTICK_ONE_MILLISECOND - 1;

  // Reset the Count Register, and the global millis counter to 0
  SysTick->CNT = 0x00000000;
  systick_millis = 0x00000000;

  // Set the SysTick Configuration
  // NOTE: By not setting SYSTICK_CTLR_STRE, we maintain compatibility with
  // busywait delay funtions used by ch32v003_fun.
  SysTick->CTLR |= SYSTICK_CTLR_STE |   // Enable Counter
                   SYSTICK_CTLR_STIE |  // Enable Interrupts
                   SYSTICK_CTLR_STCLK;  // Set Clock Source to HCLK/1

  // Enable the SysTick IRQ
  NVIC_EnableIRQ(SysTicK_IRQn);
}

/*
 * SysTick ISR - must be lightweight to prevent the CPU from bogging down.
 * Increments Compare Register and systick_millis when triggered (every 1ms)
 */
void SysTick_Handler(void) {
  // Increment the Compare Register for the next trigger
  // If more than this number of ticks elapse before the trigger is reset,
  // you may miss your next interrupt trigger
  // (Make sure the IQR is lightweight and CMP value is reasonable)
  SysTick->CMP += SYSTICK_ONE_MILLISECOND;

  // Clear the trigger state for the next IRQ
  SysTick->SR = 0x00000000;

  // Increment the milliseconds count
  systick_millis++;
}