TMS320F28335: eQEP example question

Yang Sun

Hi everyone,

I'm trying to apply eQEP function working with my motor control code. I'm currently studying the example code Example_2833xEqep_pos_speed.

In this code, the unit timer is 10ms, but my control period is 0.1ms. Can I change the unit timer somehow for higher precision?

Also. The speed and angle calculation is motivated by an ePWM interrupt, But I'm not sure what's the interrupt period. Could it be synchronized with my controller which means the period is 0.1ms. I attached the ePWM setup code below.

#include "DSP28x_Project.h" // Device Headerfile and Examples Include File
#include "Example_posspeed.h" // Example specific Include file

#if (CPU_FRQ_150MHZ)
#define CPU_CLK 150e6
#endif
#if (CPU_FRQ_100MHZ)
#define CPU_CLK 100e6
#endif

#define PWM_CLK 0 // 5kHz (300rpm) EPWM1 frequency. Freq. can be changed here
#define SP CPU_CLK/(2*PWM_CLK)
#define TBCTLVAL 0x200E // up-down count, timebase=SYSCLKOUT

void initEpwm()
{
EPwm4Regs.ETSEL.all=0x0A; // Interrupt on PRD
EPwm4Regs.ETPS.all=1;
EPwm4Regs.ETFLG.all=0;
EPwm4Regs.ETCLR.all=0;
EPwm4Regs.ETFRC.all=0;

EPwm4Regs.PCCTL.all=0;

EPwm4Regs.TBCTL.all=0x0010+TBCTLVAL; // Enable Timer
EPwm4Regs.TBPRD=SP;
}

Thanks，

Yang Sun

over 8 years ago

0 Baskaran Chidambaram over 8 years ago

TI__Genius 17370 points

Hello,
I am writing to let you know that a C2000 team member has been assigned to this post and should be answering shortly.

0 Yanming Luo over 8 years ago in reply to Baskaran Chidambaram

TI__Guru** 117000 points

Often, 100Hz unit timer of QEP is enough for most cases. You can change the QEP unit timer period to 0.1ms according to the system requirement, and you can't improve position precision by decrease unit timer, a slow QEP unit timer is more flexible for the speed and position calculation of low speed.
The QEP calculation doesn't depend on EPWM timer, and you can set EPWM timer to any value based the control bandwidth.

0 Yang Sun over 8 years ago in reply to Yanming Luo

Prodigy 150 points

Hi Baskaran and Yanming
Thanks for your response. According to your answer, I can use a 100Hz unit timer of QEP for my real time controller, even if the controller need to read the current speed and position every 0.1 ms. The only thing I suppose to change is set the epwm interrupt period to 0.1ms. Is my understanding right?

Thanks,
Yang Sun

0 Yanming Luo over 8 years ago in reply to Yang Sun

TI__Guru** 117000 points

Right. You can calculate the rotor speed and position in the control timers like 0.1ms, and don't need to change the QEP unit timer.

C2000™︎ microcontrollers

C2000 microcontrollers forum

TMS320F28335: eQEP example question