NXP Kinetis系列 KV58微控制器FTM模块食用指南

本文主要介绍利用FTM模块输出pwm波和利用FTM模块进行正交解码

FTM模块简介

FTM模块是一个多功能定时器模块,主要功能有,PWM输出、输入捕捉、输出比较、定时中断、脉冲加减计数、脉冲周期脉宽测量.在KV58中,共有FTM0,FTM1,FTM2,FTM3四个独立的FTM模块.其中FTM0和FTM3有8个通道,可用于电机或舵机的PWM输出,但不具备正交解码功能,也就是对旋转编码器输入的正反向计数功能.而FTM1和FTM2则具备正交解码功能,但是FTM1和FTM2各只有两个通道.FTM模块的时间基准来自一个16位的计数器,该计数器的值可读取,即可作为无符号数对待,也可作为有符号数的补码对待.

FTM模块与TPM差异

熟悉恩智浦 Kinetis MCU 的朋友会发现,Kinetis 各个系列都有某种联系或者可以称为一脉相承吧！举个 L 系列的 TPM 与 K 系列的 FTM 例子吧.根据参考手册的叙述,FTM 模块是 TPM 模块改进而来的一种定时器模块,即飞思卡尔在它的 8 位单片机 HCS08 系列上应用多年的定时器模块. FTM 模块在扩展了许多功能,为 TPM 提供了低功耗和向后兼容的特性.这些增强的的功能有：有符号型计数器,硬件增加死区,故障控制输入,增强触发功能,初始化和极性控制.

FTM模块特性

挑重点来说大概就是

  • PWM输出
  • PWM死区补偿
  • 输入计数
  • 正交解码
  • 兼容TPM模块

等等.以下是官方的解释:

44.2.2 Features

The FTM features include:

  • FTM source clock is selectable.
  • The source clock can be the system clock, the fixed frequency clock, or an external clock
  • Fixed frequency clock is an additional clock input to allow the selection of an on chip clock source other than the system clock
  • Selecting external clock connects FTM clock to a chip level input pin therefore allowing to synchronize the FTM counter with an off chip clock source
  • Prescaler divide-by 1, 2, 4, 8, 16, 32, 64, or 128
  • 16-bit counter
  • It can be a free-running counter or a counter with initial and final value
  • The counting can be up or up-down
  • Each channel can be configured for input capture, output compare, or edge-aligned PWM mode
  • In Input Capture mode:
  • The capture can occur on rising edges, falling edges or both edges
    *An input filter can be selected for some channels
  • In Output Compare mode the output signal can be set, cleared, or toggled on match
  • All channels can be configured for center-aligned PWM mode
  • Each pair of channels can be combined to generate a PWM signal with independent control of both edges of PWM signal
  • The FTM channels can operate as pairs with equal outputs, pairs with complementary outputs, or independent channels with independent outputs
  • The deadtime insertion is available for each complementary pair
  • Generation of match triggers
  • Initialization trigger
  • Software control of PWM outputs
  • Up to 4 fault inputs for global fault control
  • The polarity of each channel is configurable
  • The generation of an interrupt per channel
  • The generation of an interrupt when the counter overflows
  • The generation of an interrupt when the fault condition is detected
  • Synchronized loading of write buffered FTM registers >* Write protection for critical registers
  • Backwards compatible with TPM
  • Testing of input captures for a stuck at zero and one conditions
  • Dual edge capture for pulse and period width measurement
  • Quadrature decoder with input filters, relative position counting, and interrupt on position count or capture of position count on external event

FTM模块构造

FTM模块简图

由图可以看出,FTM模块的核心是一个16位计数器,所有通道共用唯一一个计数器.传入FTM模块的时钟(可以是内部时钟也可以是外部脉冲)经预分频器分频后传入FTM的16位计数器,再连接至各通道.所以一个FTM模块所有通道输出频率是相同的,并且只能选择一个时钟源,也就是说一个FTM模块不能同时做到正交解码和PWM输出.另外各相邻通道组成一个通道对,由一个控制器来控制.此外还可以发现所有中断共享一个中断号,FTM中断也是先中断再判断中断类型.

FTM寄存器

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typedef struct {
  __IO uint32_t SC;                                /**< Status And Control, offset: 0x0 */
  __IO uint32_t CNT;                               /**< Counter, offset: 0x4 */
  __IO uint32_t MOD;                               /**< Modulo, offset: 0x8 */
  struct {                                         /* offset: 0xC, array step: 0x8 */
    __IO uint32_t CnSC;                              /**< Channel (n) Status And Control, array offset: 0xC, array step: 0x8 */
    __IO uint32_t CnV;                               /**< Channel (n) Value, array offset: 0x10, array step: 0x8 */
  } CONTROLS[8];
  __IO uint32_t CNTIN;                             /**< Counter Initial Value, offset: 0x4C */
  __IO uint32_t STATUS;                            /**< Capture And Compare Status, offset: 0x50 */
  __IO uint32_t MODE;                              /**< Features Mode Selection, offset: 0x54 */
  __IO uint32_t SYNC;                              /**< Synchronization, offset: 0x58 */
  __IO uint32_t OUTINIT;                           /**< Initial State For Channels Output, offset: 0x5C */
  __IO uint32_t OUTMASK;                           /**< Output Mask, offset: 0x60 */
  __IO uint32_t COMBINE;                           /**< Function For Linked Channels, offset: 0x64 */
  __IO uint32_t DEADTIME;                          /**< Deadtime Insertion Control, offset: 0x68 */
  __IO uint32_t EXTTRIG;                           /**< FTM External Trigger, offset: 0x6C */
  __IO uint32_t POL;                               /**< Channels Polarity, offset: 0x70 */
  __IO uint32_t FMS;                               /**< Fault Mode Status, offset: 0x74 */
  __IO uint32_t FILTER;                            /**< Input Capture Filter Control, offset: 0x78 */
  __IO uint32_t FLTCTRL;                           /**< Fault Control, offset: 0x7C */
  __IO uint32_t QDCTRL;                            /**< Quadrature Decoder Control And Status, offset: 0x80 */
  __IO uint32_t CONF;                              /**< Configuration, offset: 0x84 */
  __IO uint32_t FLTPOL;                            /**< FTM Fault Input Polarity, offset: 0x88 */
  __IO uint32_t SYNCONF;                           /**< Synchronization Configuration, offset: 0x8C */
  __IO uint32_t INVCTRL;                           /**< FTM Inverting Control, offset: 0x90 */
  __IO uint32_t SWOCTRL;                           /**< FTM Software Output Control, offset: 0x94 */
  __IO uint32_t PWMLOAD;                           /**< FTM PWM Load, offset: 0x98 */
} FTM_Type;

需要注意的是FTM1和FTM2的CONTROLS[8]寄存器的后6位是没有的.

PWM产生

PWM几种模式

PWM寄存器实例

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void ftm_pwm_init(FTM_Type* ftmn, uint8_t ch, uint32_t freq, uint32_t duty)
{
  uint32_t clk_hz ;
  uint16_t mod;
  uint8_t  ps;
  uint16_t cv;
  if(ftmn==FTM0)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM0_MASK; //打开模块时钟
  }
  else if(ftmn==FTM1)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM1_MASK;
  }
  else if(ftmn==FTM2)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM2_MASK;
  }
  else if(ftmn==FTM3)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM3_MASK;
  }
  
  clk_hz = CLOCK_GetBusClkFreq();     // bus频率
  mod = (clk_hz >> 16 ) / freq ;      // 临时用 mod 缓存一下
  ps = 0;
  while((mod >> ps) >= 1)             // 等 (mod >> ps) < 1 才退出 while 循环 ，即求 PS 的最小值
  {
      ps++;
  }
  assert(ps <= 0x07);                 // 断言， PS 最大为 0x07 ，超过此值，则 PWM频率设置过低，或 Bus 频率过高
  mod = (clk_hz >> ps) / freq;        // 求 MOD 的值
  
  if(ftmn==FTM0)
  {
    cv = (duty * (mod - 0 + 1)) / FTM0_PRECISON;
  }
  else if(ftmn==FTM1)
  {
    cv = (duty * (mod - 0 + 1)) / FTM1_PRECISON;
  }
  else if(ftmn==FTM2)
  {
    cv = (duty * (mod - 0 + 1)) / FTM2_PRECISON;
  }
  else if(ftmn==FTM3)
  {
    cv = (duty * (mod - 0 + 1)) / FTM3_PRECISON;
  }
  
  ftmn->SC |= FTM_SC_PS(ps);  //设置预分频系数
  
  FTM0->MOD = mod;            //设置计数上限
  
  ftmn->CONTROLS[ch].CnSC &=~FTM_CnSC_ELSA_MASK;
  ftmn->CONTROLS[ch].CnSC |= ( FTM_CnSC_MSB_MASK | FTM_CnSC_ELSB_MASK | FTM_CnSC_DMA_MASK); //选择模式为边沿对齐PWM,具体见上图(配置完这一步PWM波已经开始输出)
  ftmn->CONTROLS[ch].CnV = cv; //通道占空比寄存器,设置占空比
  
  ftmn->CNTIN = 0; //设置计数下限为0
}

正交解码

FTM模块正交解码分为两种模式,分别是AB向模式和正交模式,平时使用较多的是正交模式.

AB向模式:

正交模式:

此外,输入通道还有硬件滤波功能,可以减小干扰.正交解码后的脉冲计数值存在CNT寄存器中,读取该寄存器不会自动清除寄存器的值.周期读取该寄存器值并且清空配合编码器就可以计算出转动速度.

正交解码实例

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void ftm_quad_init(FTM_Type* ftmn)
{
  
  if(ftmn==FTM0)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM0_MASK; //打开模块时钟
  }
  else if(ftmn==FTM1)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM1_MASK;
  }
  else if(ftmn==FTM2)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM2_MASK;
  }
  else if(ftmn==FTM3)
  {
    SIM->SCGC6 |= SIM_SCGC6_FTM3_MASK;
  }
  
  ftmn->MODE |= FTM_MODE_WPDIS_MASK; //关闭写保护
  ftmn->MODE |= FTM_MODE_FTMEN_MASK; //使能FTM功能,不然就只能使用TPM的功能
  
  ftmn->QDCTRL |= FTM_QDCTRL_QUADMODE_MASK; //选择正交解码模式
   
  ftmn->CNTIN = 0; //设置计数下限为0
  
  ftmn->MOD = FTM_MOD_MOD_MASK; //设置计数上限为最大值(free running模式)
  
  ftmn->QDCTRL |= FTM_QDCTRL_QUADEN_MASK; //使能正交解码
  
  ftmn->CNT = 0; //清除计数器中的值
}