bsb1/arch/lapic_timer.cc

#include "lapic.h"
#include "lapic_registers.h"
#include "core.h"
#include "pit.h"

#include "../debug/output.h"

namespace LAPIC {
namespace Timer {

/*! \brief Timer Delivery Status */
enum DeliveryStatus { IDLE = 0, SEND_PENDING = 1 };

/*! \brief Timer Mode */
enum TimerMode {
  ONE_SHOT = 0,
  PERIODIC = 1,
  DEADLINE = 2
  // reserved
};

/*! \brief Timer Mask */
enum Mask { NOT_MASKED = 0, MASKED = 1 };

static const Register INVALID_DIV = 0xff;

/*! \brief LAPIC-Timer Control Register
 *
 * \see [ISDMv3 10.5.1 Local Vector Table](intel_manual_vol3.pdf#page=375)
 */
union ControlRegister {
  struct {
    uint32_t vector : 8;  ///< Vector
    uint32_t : 4;
    DeliveryStatus delivery_status : 1;  ///< Delivery Status (readonly)
    uint32_t : 3;
    Mask masked : 1;  ///< Interrupt Mask (if set, interrupt will not trigger)
    TimerMode timer_mode : 2;  ///< Timer Mode
    uint32_t : 13;
  };
  Register value;
} __attribute__((packed));

/*! \brief LAPIC timer divider table
 *
 * \see [ISDMv3 10.5.4 APIC Timer](intel_manual_vol3.pdf#page=378)
 */
static const Register div_masks[] = {
    0xb,  ///< divides by   1
    0x0,  ///< divides by   2
    0x1,  ///< divides by   4
    0x2,  ///< divides by   8
    0x3,  ///< divides by  16
    0x8,  ///< divides by  32
    0x9,  ///< divides by  64
    0xa   ///< divides by 128
};

/*! \brief Calculate the bit mask for the LAPIC-timer divider.
 *  \param div Divider, must be power of two: 1, 2, 4, 8, 16, 32, 64, 128
 *  \return Bit mask for LAPIC::setTimer() or `0xff` if `div` is invalid.
 */
static Register getClockDiv(uint8_t div) {
  switch (div) {
    case   1: return div_masks[0];
    case   2: return div_masks[1];
    case   4: return div_masks[2];
    case   8: return div_masks[3];
    case  16: return div_masks[4];
    case  32: return div_masks[5];
    case  64: return div_masks[6];
    case 128: return div_masks[7];
    default : return 0xff;
  }
}
/*! \brief Calculate the LAPIC-timer divider for the bit mask.
 *  \param div_mask The bit mask, must be one of: 0xb, 0x0, 0x1, 0x2, 0x3, 0x8, 0x9, 0xa
 *  \return LAPIC-timer divider or `0xff` if `div_mask` is invalid.
 */
static uint8_t fromClockDiv(Register div_mask) {
  if (div_mask == div_masks[0]) return   1;
  if (div_mask == div_masks[1]) return   2;
  if (div_mask == div_masks[2]) return   4;
  if (div_mask == div_masks[3]) return   8;
  if (div_mask == div_masks[4]) return  16;
  if (div_mask == div_masks[5]) return  32;
  if (div_mask == div_masks[6]) return  64;
  if (div_mask == div_masks[7]) return 128;
  return 0xff;
}


uint32_t ticks(void) {
  static uint32_t ticks = 0;  // ticks per millisecond
  if (ticks != 0) return ticks;

  // Prepare Counter
  LAPIC::Timer::set(0, 1, 0, false, true);
  
  // Set timer for 10ms
  PIT::set(10 * 1000); 
  // Start LAPIC-Timer
  LAPIC::write(TIMER_INITIAL_COUNTER, UINT32_MAX);
  PIT::waitForTimeout();
  // Get final Count
  uint32_t counter = LAPIC::read(TIMER_CURRENT_COUNTER);
  // Disable LAPIC-Timer
  LAPIC::write(TIMER_INITIAL_COUNTER, 0);
  // Calculate tick count.
  ticks = (UINT32_MAX - counter) / 10;

  DBG << "LAPIC-Timer calibration using PIT" << endl;
  return ticks;
}

void set(uint32_t counter, uint8_t divide, uint8_t vector, bool periodic,
         bool masked) {
  if (divide == 0 || (divide & (divide - 1)) != 0) {
    // Not a power of 2
    return;
  }

  ControlRegister tcr;
  tcr.vector = Core::Interrupt::Vector::TIMER;
  tcr.timer_mode = periodic ? PERIODIC : ONE_SHOT;
  tcr.masked = masked ? MASKED : NOT_MASKED;
  LAPIC::write(TIMER_CONTROL, tcr.value);
  
  LAPIC::write(TIMER_DIVIDE_CONFIGURATION, getClockDiv(divide));
  LAPIC::write(TIMER_INITIAL_COUNTER, counter);
}

bool setup(uint32_t us) {
  uint64_t timer_ticks = (static_cast<uint64_t>(ticks()) * us) / 1000ULL;
    
  uint8_t divisor = 1;
  while (timer_ticks > UINT32_MAX) {
    // While timer_ticks is to large to fit in 32bits.
    timer_ticks >>= 1;
    divisor <<= 1;
  }
  if (divisor > 128) 
      return false; // Timer interval is to large.
    
  // Setup Masked interrupts to effectively disable the timer.
  set(static_cast<uint32_t>(timer_ticks), divisor, Core::Interrupt::TIMER, true, true);
  return true;
}

uint32_t interval() {
  uint32_t timer_ticks = LAPIC::read(TIMER_INITIAL_COUNTER);
  uint32_t divisor = fromClockDiv(LAPIC::read(TIMER_DIVIDE_CONFIGURATION));

  uint64_t us = (static_cast<uint64_t>(timer_ticks) * divisor * 1000ULL) / static_cast<uint64_t>(ticks());
  return static_cast<uint32_t>(us);
}

void activate() {
  uint32_t timer_ticks = LAPIC::read(TIMER_INITIAL_COUNTER);
  // Disable Counter to avoid spouriose interrupts.
  LAPIC::write(TIMER_INITIAL_COUNTER, 0);

  // Activate Timer interrupts.
  setMasked(false);

  // enable counter with correct value.
  LAPIC::write(TIMER_INITIAL_COUNTER, timer_ticks);
}

void setMasked(bool masked) { 
  ControlRegister tcr;
  tcr.value = LAPIC::read(TIMER_CONTROL);
  tcr.masked = masked ? MASKED : NOT_MASKED;
  LAPIC::write(TIMER_CONTROL, tcr.value);
}
}  // namespace Timer
}  // namespace LAPIC