Hallo
We are to use a TI F28377D to control a 3 phase ac motor where we use an encoder for the position and speed feedback. I have been looking at the examples included in the codecomposer and found the example called "eqep_pos_speed_cpu1" which explains how to use the predefined eqep structure. I am still relative new to during direct programming to a micro processor and was hoping a kind soul would maybe explain how the current code works, because the math explained in the comment section of the script is quite easy, but I can't see the correlation between the math and the code they have written, and when I try to rewrite the code according to the math it does not work. The section of the code which is giving me troubles is this one
//**** Position calculation - mechanical and electrical motor angle ****//
p->DirectionQep = EQep1Regs.QEPSTS.bit.QDF; // Motor direction: 0=CCW/reverse, 1=CW/forward
pos16bval=(unsigned int)EQep1Regs.QPOSCNT; // capture position once per QA/QB period
p->theta_raw = pos16bval+ p->cal_angle; // raw theta = current pos. + ang. offset from QA
// The following lines calculate p->theta_mech ~= QPOSCNT/mech_scaler [current cnt/(total cnt in 1 rev.)]
// where mech_scaler = 4000 cnts/revolution
tmp = (long)((long)p->theta_raw*(long)p->mech_scaler); // Q0*Q26 = Q26 // <- what does this mean and why is this soundingly a product and not devision
tmp &= 0x03FFF000; // <- Where did this address come from?
p->theta_mech = (int)(tmp>>11); // Q26 -> Q15 //<- Why does they now do a shift?
p->theta_mech &= 0x7FFF; //
// The following lines calculate p->elec_mech
p->theta_elec = p->pole_pairs*p->theta_mech; // Q0*Q15 = Q15
p->theta_elec &= 0x7FFF;
// Check an index occurrence
if (EQep1Regs.QFLG.bit.IEL == 1)
{
p->index_sync_flag = 0x00F0;
EQep1Regs.QCLR.bit.IEL=1; // Clear __interrupt flag
}
I have added a few comments in the section the confuses me, but please bear in mind, that I am new to the syntax, and therefor there is proberly something obvious that I am missing. I simply hope someone could spare 5 mins to explain the code so that I might understand how rewrite the code to something more like the math and still use the nicely predefined structure.
I have added the full code here for full overview
//###########################################################################
//
// FILE: Example_posspeed.c
//
// TITLE: Pos/speed measurement using EQEP peripheral
//
// DESCRIPTION:
//
// This file includes the EQEP initialization and position and speed calculation
// functions called by Eqep_posspeed.c. The position and
// speed calculation steps performed by POSSPEED_Calc() at SYSCLKOUT = 200 MHz are described below:
//
//
// 1. This program calculates: **theta_mech**
//
// theta_mech = QPOSCNT/mech_Scaler = QPOSCNT/4000, where 4000 is the number of
// counts in 1 revolution.(4000/4 = 1000 line/rev. quadrature encoder)
//
// 2. This program calculates: **theta_elec**
//
// theta_elec = (# pole pairs) * theta_mech = 2*QPOSCNT/4000 for this example
//
// 3. This program calculates: **SpeedRpm_fr**
//
// SpeedRpm_fr = [(x2-x1)/4000]/T - Equation 1
// Note (x2-x1) = difference in number of QPOSCNT counts. Dividing (x2-x1) by
// 4000 gives position relative to Index in one revolution.
// If base RPM = 6000 rpm: 6000 rpm = [(x2-x1)/4000]/10ms - Equation 2
// = [(x2-x1)/4000]/(.01s*1 min/60 sec)
// = [(x2-x1)/4000]/(1/6000) min
// max (x2-x1) = 4000 counts, or 1 revolution in 10 ms
//
//
// If both sides of Equation 2 are divided by 6000 rpm, then:
// 1 = [(x2-x1)/4000] rev./[(1/6000) min * 6000rpm]
// Because (x2-x1) must be <4000 (max) for QPOSCNT increment,
// (x2-x1)/4000 < 1 for CW rotation
// And because (x2-x1) must be >-4000 for QPOSCNT decrement,
// (x2-x1)/4000>-1 for CCW rotation
// speed_fr = [(x2-x1)/4000]/[(1/6000) min * 6000rpm]
// = (x2-x1)/4000 - Equation 3
//
// To convert speed_fr to RPM, multiply Equation 3 by 6000 rpm
// SpeedRpm_fr = 6000rpm *(x2-x1)/4000 - Final Equation
//
//
// 2. **min rpm ** = selected at 10 rpm based on CCPS prescaler options available (128 is greatest)
//
// 3. **SpeedRpm_pr**
// SpeedRpm_pr = X/(t2-t1) - Equation 4
// where X = QCAPCTL [UPPS]/4000 rev. (position relative to Index in 1 revolution)
// If max/base speed = 6000 rpm:
// 6000 = (32/4000)/[(t2-t1)/(200MHz/64)]
// where 32 = QCAPCTL [UPPS] (Unit timeout - once every 32 edges)
// 32/4000 = position in 1 revolution (position as a fraction of 1 revolution)
// t2-t1/(200MHz/64), t2-t1= # of QCAPCLK cycles, and
// QCAPCLK cycle = 1/(200MHz/64)
// = QCPRDLAT
//
// So: 6000 rpm = [32(200MHz/64)*60s/min]/[4000(t2-t1)]
// t2-t1 = [32(200MHz/64)*60s/min]/(4000*6000rpm) - Equation 5
// = 250 CAPCLK cycles = maximum (t2-t1) = SpeedScaler
//
// Divide both sides by (t2-t1), and:
// 1 = 32/(t2-t1) = [32(200MHz/64)*60 s/min]/(4000*6000rpm)]/(t2-t1)
// Because (t2-t1) must be < 250 for QPOSCNT increment:
// 250/(t2-t1) < 1 for CW rotation
// And because (t2-t1) must be >-250 for QPOSCNT decrement:
// 250/(t2-t1)> -1 for CCW rotation
//
// eed_pr = 250/(t2-t1)
// or [32(200MHz/64)*60 s/min]/(4000*6000rpm)]/(t2-t1) - Equation 6
//
// To convert speed_pr to RPM:
// Multiply Equation 6 by 6000rpm:
// SpeedRpm_fr = 6000rpm * [32(200MHz/64)*60 s/min]/[4000*6000rpm*(t2-t1)]
// = [32(200MHz/64)*60 s/min]/[4000*(t2-t1)]
// or [(32/4000)rev * 60 s/min]/[(t2-t1)(QCPRDLAT)]- Final Equation
//
//
// More detailed calculation results can be found in the Example_freqcal.xls
// spreadsheet included in the example folder.
//
//
//
// This file contains source for the posspeed module
//
//###########################################################################
// Original Author: SD
//
// $TI Release: F2837xD Support Library v100 $
// $Release Date: Mon Dec 9 12:58:09 CST 2013 $
//###########################################################################
#include "F28x_Project.h" // Device Headerfile and Examples Include File
#include "Example_posspeed.h" // Example specific Include file
void POSSPEED_Init(void)
{
EQep1Regs.QUPRD=2000000; // Unit Timer for 100Hz at 200 MHz SYSCLKOUT
EQep1Regs.QDECCTL.bit.QSRC=00; // QEP quadrature count mode
EQep1Regs.QEPCTL.bit.FREE_SOFT=2;
EQep1Regs.QEPCTL.bit.PCRM=00; // PCRM=00 mode - QPOSCNT reset on index event
EQep1Regs.QEPCTL.bit.UTE=1; // Unit Timeout Enable
EQep1Regs.QEPCTL.bit.QCLM=1; // Latch on unit time out
EQep1Regs.QPOSMAX=0xffffffff;
EQep1Regs.QEPCTL.bit.QPEN=1; // QEP enable
EQep1Regs.QCAPCTL.bit.UPPS=5; // 1/32 for unit position
EQep1Regs.QCAPCTL.bit.CCPS=6; // 1/64 for CAP clock
EQep1Regs.QCAPCTL.bit.CEN=1; // QEP Capture Enable
}
void POSSPEED_Calc(POSSPEED *p)
{
long tmp;
unsigned int pos16bval,temp1;
_iq Tmp1,newp,oldp;
//**** Position calculation - mechanical and electrical motor angle ****//
p->DirectionQep = EQep1Regs.QEPSTS.bit.QDF; // Motor direction: 0=CCW/reverse, 1=CW/forward
pos16bval=(unsigned int)EQep1Regs.QPOSCNT; // capture position once per QA/QB period
p->theta_raw = pos16bval+ p->cal_angle; // raw theta = current pos. + ang. offset from QA
// The following lines calculate p->theta_mech ~= QPOSCNT/mech_scaler [current cnt/(total cnt in 1 rev.)]
// where mech_scaler = 4000 cnts/revolution
//tmp = (long)((long)pos16bval/(long)4000.0);
tmp = (long)((long)p->theta_raw*(long)p->mech_scaler); // Q0*Q26 = Q26
tmp &= 0x03FFF000;
p->theta_mech = (int)(tmp>>11); // Q26 -> Q15
p->theta_mech &= 0x7FFF;
// The following lines calculate p->elec_mech
p->theta_elec = p->pole_pairs*p->theta_mech; // Q0*Q15 = Q15
p->theta_elec &= 0x7FFF;
// Check an index occurrence
if (EQep1Regs.QFLG.bit.IEL == 1)
{
p->index_sync_flag = 0x00F0;
EQep1Regs.QCLR.bit.IEL=1; // Clear __interrupt flag
}
//**** High Speed Calculation using QEP Position counter ****//
// Check unit Time out-event for speed calculation:
// Unit Timer is configured for 100Hz in INIT function
if(EQep1Regs.QFLG.bit.UTO==1) // If unit timeout (one 100Hz period)
{
/** Differentiator **/
// The following lines calculate position = (x2-x1)/4000 (position in 1 revolution)
pos16bval=(unsigned int)EQep1Regs.QPOSLAT; // Latched POSCNT value
tmp = (long)((long)pos16bval*(long)p->mech_scaler); // Q0*Q26 = Q26
tmp &= 0x03FFF000;
tmp = (int)(tmp>>11); // Q26 -> Q15
tmp &= 0x7FFF;
newp=_IQ15toIQ(tmp);
oldp=p->oldpos;
if (p->DirectionQep==0) // POSCNT is counting down
{
if (newp>oldp)
Tmp1 = - (_IQ(1) - newp + oldp); // x2-x1 should be negative
else
Tmp1 = newp -oldp;
}
else if (p->DirectionQep==1) // POSCNT is counting up
{
if (newp<oldp)
Tmp1 = _IQ(1) + newp - oldp;
else
Tmp1 = newp - oldp; // x2-x1 should be positive
}
if (Tmp1>_IQ(1))
p->Speed_fr = _IQ(1);
else if (Tmp1<_IQ(-1))
p->Speed_fr = _IQ(-1);
else
p->Speed_fr = Tmp1;
// Update the electrical angle
p->oldpos = newp;
// Change motor speed from pu value to rpm value (Q15 -> Q0)
// Q0 = Q0*GLOBAL_Q => _IQXmpy(), X = GLOBAL_Q
p->SpeedRpm_fr = _IQmpy(p->BaseRpm,p->Speed_fr);
//=======================================
EQep1Regs.QCLR.bit.UTO=1; // Clear __interrupt flag
}
//**** Low-speed computation using QEP capture counter ****//
if(EQep1Regs.QEPSTS.bit.UPEVNT==1) // Unit position event
{
if(EQep1Regs.QEPSTS.bit.COEF==0) // No Capture overflow
temp1=(unsigned long)EQep1Regs.QCPRDLAT; // temp1 = t2-t1
else // Capture overflow, saturate the result
temp1=0xFFFF;
p->Speed_pr = _IQdiv(p->SpeedScaler,temp1); // p->Speed_pr = p->SpeedScaler/temp1
Tmp1=p->Speed_pr;
if (Tmp1>_IQ(1))
p->Speed_pr = _IQ(1);
else
p->Speed_pr = Tmp1;
// Convert p->Speed_pr to RPM
if (p->DirectionQep==0) // Reverse direction = negative
p->SpeedRpm_pr = -_IQmpy(p->BaseRpm,p->Speed_pr); // Q0 = Q0*GLOBAL_Q => _IQXmpy(), X = GLOBAL_Q
else // Forward direction = positive
p->SpeedRpm_pr = _IQmpy(p->BaseRpm,p->Speed_pr); // Q0 = Q0*GLOBAL_Q => _IQXmpy(), X = GLOBAL_Q
EQep1Regs.QEPSTS.all=0x88; // Clear Unit position event flag
// Clear overflow error flag
}
}
