stm8l101 LSI 校准是扯淡吗？

只看该作者 · 2015-1-8 15:16

标题用“扯淡”，只为吸引大家注意，呵呵

看了它的例程就，好像校准起不到作用

下面是例程的主程序片段，只要看最后三行
CLK_MasterPrescalerConfig(CLK_MasterPrescaler_HSIDiv1);
00072
00073 /* Enable SPI clock */
00074 CLK_PeripheralClockConfig(CLK_Peripheral_SPI, ENABLE);
00075 CLK_PeripheralClockConfig(CLK_Peripheral_TIM2, ENABLE);
00076 CLK_PeripheralClockConfig(CLK_Peripheral_AWU, ENABLE);
00077
00078 /* Initialization of I/Os in Output Mode */
00079 GPIO_Init(LEDS_PORT, (LED2_PIN | LED3_PIN | LED4_PIN), GPIO_Mode_Out_PP_Low_Fast);
00080
00081 /* Initialization of I/O in Input Mode with Interrupt */
00082 GPIO_Init(BUTTON_PORT, BUTTON_PIN, GPIO_Mode_In_FL_IT);
00083
00084 /* Initialization of the Interrupt sensitivity */
00085 EXTI_SetPinSensitivity(EXTI_Pin_5, EXTI_Trigger_Falling);
00086
00087 /* Initialization of AWU */
00088 /* LSI calibration for accurate auto wake up time base*/
00089 AWU_LSICalibrationConfig(LSIMeasurment());
00090
00091 /* The delay corresponds to the time we will stay in Halt mode */
00092 AWU_Init(AWU_Timebase_12s);
00093
看一下 AWU_LSICalibrationConfig 函数的内容

00129 void AWU_LSICalibrationConfig(uint32_t LSIFreqHz)
00130 {
00131
00132    uint16_t lsifreqkhz = 0x0;
00133    uint16_t A = 0x0;
00134
00135    /* Check parameter */
00136    assert_param(IS_LSI_FREQUENCY(LSIFreqHz));
00137
00138    lsifreqkhz = (uint16_t)(LSIFreqHz / 1000); /* Converts value in kHz */
00139
00140    /* Calculation of AWU calibration value */
00141
00142    A = (uint16_t)(lsifreqkhz >> 2U); /* Division by 4, keep integer part only */
00143
00144    if ((4U * A) >= ((lsifreqkhz - (4U * A)) * (1U + (2U * A))))
00145    {
00146       AWU->APR = (uint8_t)(A - 2U);
00147    }
00148    else
00149    {
00150       AWU->APR = (uint8_t)(A - 1U);
00151    }
00152
00153    /* Set the MR bit to load the new value to the prescalers */
00154    AWU->CSR |= AWU_CSR_MR;
00155
00156 }
校准的结果最终反应在 AWU->APR 的值

然后再看一下  AWU_Init();函数
00073 */
00074 void AWU_Init(AWU_Timebase_TypeDef AWU_TimeBase)
00075 {
00076
00077    /* Check parameter */
00078    assert_param(IS_AWU_TIMEBASE(AWU_TimeBase));
00079
00080    /* Enable the AWU peripheral */
00081    AWU->CSR |= AWU_CSR_AWUEN;
00082
00083    /* Set the TimeBase */
00084    AWU->TBR &= (uint8_t)(~AWU_TBR_AWUTB);
00085    AWU->TBR |= TBR_Array[(uint8_t)AWU_TimeBase];
00086
00087    /* Set the APR divider */
00088    AWU->APR &= (uint8_t)(~AWU_APR_APR);
00089    AWU->APR |= APR_Array[(uint8_t)AWU_TimeBase];
00090
00091 }

它又把 AWU->APR 给刷新了
这样校准后有什么用？实测也是没用的。
上面的程序全部来自stm8l101的固件库

照例程没用，请高手指点应该怎么用。

只看该作者 · 2016-8-22 15:10

我也不太理解这个低速时钟是怎么校准的

只看该作者 · 2016-8-22 15:11

/**
  * @brief  Update APR register with the measured LSI frequency.
  * @NOTE AWU must be disabled to avoid unwanted interrupts.
  * @note Prescaler calculation:
  *       A is the integer part of LSIFreqkHz/4 and x the decimal part.
  *       x <= A/(1+2A) is equivalent to A >= x(1+2A)
  *       and also to 4A >= 4x(1+2A) [F1]
  *       but we know that A + x = LSIFreqkHz/4 ==> 4x = LSIFreqkHz-4A
  *       so [F1] can be written :
  *       4A >= (LSIFreqkHz-4A)(1+2A)
  * @param  LSIFreqHz Low Speed RC frequency measured by timer (in Hz).
  * @retval None
  */
void AWU_LSICalibrationConfig(uint32_t LSIFreqHz)
{

  uint16_t lsifreqkhz = 0x0;
  uint16_t A = 0x0;

  /* Check parameter */
  assert_param(IS_LSI_FREQUENCY(LSIFreqHz));

  lsifreqkhz = (uint16_t)(LSIFreqHz / 1000); /* Converts value in kHz */

  /* Calculation of AWU calibration value */

  A = (uint16_t)(lsifreqkhz >> 2U); /* Division by 4, keep integer part only */

  if ((4U * A) >= ((lsifreqkhz - (4U * A)) *(1U + (2U * A))))
  {
AWU->APR = (uint8_t)(A - 2U);
  }
  else
  {
AWU->APR = (uint8_t)(A - 1U);
  }

}
这个函数不明白~

只看该作者 · 2017-4-21 09:51

请问STM8 LSI 是怎么校准的，校准后的误差又是多少

stm8l101 LSI 校准是扯淡吗？

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