我目前正在阅读atmel上的应用笔记，其中我正在尝试理解code。该代码生成了梯形斜坡，用于控制步进电机。
我对代码不了解的一件事是将常量设置为
// Timer/Counter 1 running on 3,686MHz / 8 = 460,75kHz (2,17uS). (T1-FREQ 460750)
#define T1_FREQ 1382400
我不确定我知道为什么值是1382400而不是460750，因为以8预先分频的时钟频率是460750 ...那为什么是1382400？我想念什么吗？
.h文件
/*This file has been prepared for Doxygen automatic documentation generation.*/
/*! \file *********************************************************************
*
* \brief Header file for speed_cntr.c.
*
* - File: speed_cntr.h
* - Compiler: IAR EWAAVR 4.11A
* - Supported devices: All devices with a 16 bit timer can be used.
* The example is written for ATmega48
* - AppNote: AVR446 - Linear speed control of stepper motor
*
* \author Atmel Corporation: http://www.atmel.com \n
* Support email: [email protected]
*
* $Name: RELEASE_1_0 $
* $Revision: 1.2 $
* $RCSfile: speed_cntr.h,v $
* $Date: 2006/05/08 12:25:58 $
*****************************************************************************/
#ifndef SPEED_CNTR_H
#define SPEED_CNTR_H
/*! \brief Holding data used by timer interrupt for speed ramp calculation.
*
* Contains data used by timer interrupt to calculate speed profile.
* Data is written to it by move(), when stepper motor is moving (timer
* interrupt running) data is read/updated when calculating a new step_delay
*/
typedef struct {
//! What part of the speed ramp we are in.
unsigned char run_state : 3;
//! Direction stepper motor should move.
unsigned char dir : 1;
//! Peroid of next timer delay. At start this value set the accelration rate.
unsigned int step_delay;
//! What step_pos to start decelaration
unsigned int decel_start;
//! Sets deceleration rate.
signed int decel_val;
//! Minimum time delay (max speed)
signed int min_delay;
//! Counter used when accelerateing/decelerateing to calculate step_delay.
signed int accel_count;
} speedRampData;
/*! \Brief Frequency of timer1 in [Hz].
*
* Modify this according to frequency used. Because of the prescaler setting,
* the timer1 frequency is the clock frequency divided by 8.
*/
// Timer/Counter 1 running on 3,686MHz / 8 = 460,75kHz (2,17uS). (T1-FREQ 460750)
#define T1_FREQ 1382400
//! Number of (full)steps per round on stepper motor in use.
#define FSPR 200
#ifdef HALFSTEPS
#define SPR (FSPR*2)
#pragma message("[speed_cntr.c] *** Using Halfsteps ***")
#endif
#ifdef FULLSTEPS
#define SPR FSPR
#pragma message("[speed_cntr.c] *** Using Fullsteps ***")
#endif
#ifndef HALFSTEPS
#ifndef FULLSTEPS
#error FULLSTEPS/HALFSTEPS not defined!
#endif
#endif
// Maths constants. To simplify maths when calculating in speed_cntr_Move().
#define ALPHA (2*3.14159/SPR) // 2*pi/spr
#define A_T_x100 ((long)(ALPHA*T1_FREQ*100)) // (ALPHA / T1_FREQ)*100
#define T1_FREQ_148 ((int)((T1_FREQ*0.676)/100)) // divided by 100 and scaled by 0.676
#define A_SQ (long)(ALPHA*2*10000000000) // ALPHA*2*10000000000
#define A_x20000 (int)(ALPHA*20000) // ALPHA*20000
// Speed ramp states
#define STOP 0
#define ACCEL 1
#define DECEL 2
#define RUN 3
void speed_cntr_Move(signed int step, unsigned int accel, unsigned int decel, unsigned int speed);
void speed_cntr_Init_Timer1(void);
static unsigned long sqrt(unsigned long v);
unsigned int min(unsigned int x, unsigned int y);
//! Global status flags
extern struct GLOBAL_FLAGS status;
#endif
最佳答案
/*! \Brief Frequency of timer1 in [Hz].
*
该注释告诉您根据需要修改T1_FREQ。
* Modify this according to frequency used. Because of the prescaler setting,
* the timer1 frequency is the clock frequency divided by 8.
*/
此行为您提供了计算示例。这只是一个例子。如果需要，他们可以使用完全不同的数字。每次使用不同的预分频器或频率时，他们都不会更改一般示例。
// Timer/Counter 1 running on 3,686MHz / 8 = 460,75kHz (2,17uS). (T1-FREQ 460750)
此行是您需要更改的行。他们在代码中使用了1382400。如果您的情况需要460750，请替换数字...
#define T1_FREQ 1382400
关于c++ - 这个常数不正确吗？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/41102925/