在脉冲模式下，步进电机启动器的脉冲频率与速度成正比，函数void CalculateSModelLine(float fre[], unsigned short period[], float len, float fre_max, float fre_min, float flexible)主要目的就是生成每一个细分步加速的速度。芯片用的是stm32f103c8t6，驱动器用的是2DM420。
程序流程如下：
STM32硬件基本初始化，主要是针对定时器
调用函数CalculateSModelLine（）生 成每一个细分步定时器的自动重装载值（实际就是改变脉冲的周期）
打开定时器
更新中断发生，将数组中的数据赋值给定时器的自动重装载寄存器
跳出中断后脉冲频频率就变化了
下一次更新中断产生
对应的计算接口code:
/* calculate the Period and Freq array value, fill the Period value into the Period register during the timer interrupt.
*calculate the acceleration procedure , a totally 1000 elements array.
* parameter fre[]: point to the array that keeps the freq value.
* period[]: point to the array that keeps the timer period value.
* len: the procedure of acceleration length.it is best thing to set the float number, some compile software maybe transfer error if set it as a int
* fre_max: maximum speed, frequency vale.
* fre_min: start minimum speed, frequency vale. mind : 10000000/65535 = 152, so fre_min can't less than 152.
* flexible: flexible value. adjust the S curves
*/
void CalculateSModelLine(float fre[], unsigned short period[], float len, float fre_max, float fre_min, float flexible)
{
int i=0;
float deno ;
float melo ;
float delt = fre_max-fre_min;
for(; i;>
{
melo = flexible * (i-len/2) / (len/2);
deno = 1.0 / (1 + expf(-melo)); //expf is a library function of exponential(e)
fre[i] = delt * deno + fre_min;
period[i] = (unsigned short)(10000000.0 / fre[i]); // 10000000 is the timer driver frequency
}
return ;
}