The document discusses PWM control of servo motors using the S3C6410 microprocessor. It describes how the S3C6410 contains timers that can generate PWM signals to control servo position and speed. It provides code examples for initializing the timers for PWM output and setting the register values to control the duty cycle and period of the PWM signal. User space code is also shown for opening and configuring the PWM device files.

1. 伺服馬達控制
Joseph Chen

2. 360° Servo
伺服馬達控制主要利用PWM控制轉的方向
與轉速
360° servo 需要50Hz的脈波週期訊號 並藉由0.5~2.5ms HIGH PULSE做
控制
等於1.5ms HIGH PULSE是位於停止的狀態
小於1.5ms 順時針轉動, 若值愈小轉速可愈快
大於1.5ms 逆時針轉動,若值愈大轉速可愈快。

4. The S3C6410X RISC microprocessor comprises of
five 32-bit timers. These timers are used to
generate internal interrupts to the ARM
subsystem.
Timers 0 and 1 include a PWM function (Pulse
Width Modulation), which can drive an external
I/O signal. The PWM for timer 0 and 1 have an
optional dead-zone generator capability, which
can be utilized to support a large current device.
Timer 2, 3 and 4 are internal timers with no
output pins.

5. Clock Generation Scheme for PWM

6. PWM Function Block
TCNTB TCMPB
Manual Update=1
Auto reload=1
PCLK Prescaler Divder when TCNT reaches 0
TCNT TCMP TCNT=TCNB
TCMP=TCMPB
TCNTO
TCFG TCON
Double Buffering

7. PWM waveform

8. REGISTER MAP

10. S3C6410 的PWM 如何設定?
得到20ms的週期 (50HZ)
如果 PCLK=83MHZ, 8-bit prescaler=255 and 4-bit divider=16
Frequency=PCLK/(255+1)/16 => 20.2KHz
週期=>1/20.2K=0.0495ms
20ms/0.0495=404 --> TCNTB TOUT
Pulse Width
TCMPB setting?:
Get 2ms High Pulse width: 2ms/0.0495=40
Get 1.5ms High Pulse width: 1.5ms/0.0495=30
Get 1ms High Pulse width: 1ms/0.0495=20

11. dc_motor.c
static int __init dcm_init(void)
{
int retval;
retval = register_chrdev(DCM_MAJOR,dcm_name,&dcm_fops);
if(retval < 0)
{
printk(KERN_WARNING"Can't get major %dn",DCM_MAJOR);
return retval;
}
s3c6410_timer_setup(0,10,100,0);
pwm_init(PERIOD); //unit: 20000us
printk("Serveo_motor driver register success!n");
return 0;
}

12. static void pwm_init(unsigned long period)
{
Period=20000us
// initial the timer period
unsigned long tcnt;
時間(週期)
= Y HZ (Y次/s)* period
hi_pulse=0;
=次/s *(us/106)
tcnt=(period*(( PCLK )/((255+1)*16 )))/1000000;
printk(KERN_WARNING"%s:tcnt=%ldn",__func__,tcnt);
// tcnt =( 96000000 )/( FREQ_PWM1 *16 );
__raw_writel(tcnt, S3C_TCNTB(0));
__raw_writel(((tcnt*(0))/100), S3C_TCMPB(0));
}

13. s3c6410_timer_setup
int s3c6410_timer_setup (int channel, int usec,
unsigned long g_tcnt, unsigned long g_tcmp)
Parameters:
1) channel: PWM channel 0/1
2) usec: unused
3) g_tcnt: unused
4) g_tcmp: unused

14. /* set gpio as PWM TIMER0 to signal output*/
s3c_gpio_cfgpin(S3C64XX_GPF(14), S3C64XX_GPF14_PWM_TOUT0);
s3c_gpio_setpull(S3C64XX_GPF(14), S3C_GPIO_PULL_NONE);
tcfg1 &= ~S3C_TCFG1_MUX0_MASK;
tcfg1 |= 4; // set divider 16 , by jospeh
tcfg0 &= ~S3C_TCFG_PRESCALER0_MASK;
tcfg0 |= (PRESCALER) << S3C_TCFG_PRESCALER0_SHIFT;
tcon &= ~(7<<0);
tcon |= S3C_TCON_T0RELOAD;

15. User space Code
232, 0 /dev/pwm0
232,1 /dev/pwm1
fd_l=open(“/dev/pwm0”);
ioctl(fd_l,cmd,arg);
fd_r=open(“dev/pmm1”);
Ioctl(fd_r,cmd,arg)