grease_lighting
Well-known member
I'm planning on using the FTM as an event counter. Starting with this previous posting I've gotten some promising results. However I notice that I cannot change the count modulus with the FTM1_MOD command. It always seems to be stuck at 0x8FFF (36863 decimal). When I run the attached code it will function as expected, counting in increments of 1023, but when it gets to a count of 36828 it will roll over to a count of 987 which is probably what should happen. Is there a problem, or maybe I'm using the wrong code, in setting the count modulus to maximum 65535? or any value really? I get same results with another Teensy that I have.
If you try this remember to jumper pin 13 to pin 3.
This is my output.
If you try this remember to jumper pin 13 to pin 3.
Code:
//
// Code for Teensy 3.x to read Flex Timer quadrature counters
//
// use flex timer on pins 3 & 4
//
// reference
// https://forum.pjrc.com/threads/30822-Teensy-3-1-and-Flextimer(s)-Counting-external-pulses-accurately
// https://forum.pjrc.com/threads/26803-Hardware-Quadrature-Code-for-Teensy-3-x
//
// code mostly from reference #1
//
// Jumper LED_PIN (13) to pin 3 (clock)
// Pin #4 controls count direction. HIGH = up LOW = down
//
//
int p1;
int x;
#define LED_PIN 13
//(1) Setup statements
void setup() {
// pinMode(3, INPUT_PULLUP); // signal to count gets taken care of by PORT_PCA statements
pinMode(4, INPUT_PULLUP); // tied high to set count direction
pinMode(16, OUTPUT); // some kind of pulse output -- for debug
pinMode(LED_PIN, OUTPUT);
digitalWrite(LED_PIN, LOW);
Serial.begin(0);
while (!Serial);
//configure Flextimer 1
FTM1_MODE = FTM_MODE_WPDIS | FTM_MODE_FTMEN; //set write-protect disable (WPDIS) bit to modify other registers
Serial.print("FTM1_MODE: "); Serial.println(FTM1_MODE, BIN);
FTM1_FILTER = 0x00; // no filtering
Serial.print("FTM1_SC: "); Serial.println(FTM1_SC, BIN); // read then set to eliminate Timer Overflow Flag
FTM1_SC = 0x00; //set status/control to zero = disable all internal clock sources
Serial.print("FTM1_SC: "); Serial.println(FTM1_SC, BIN); // SC=0 does not disable quadrature mode
FTM1_QDCTRL = FTM_QDCTRL_QUADMODE | FTM_QDCTRL_QUADEN; // comes in on pin 3
Serial.print("FTM1_QDCTRL: "); Serial.println(FTM1_QDCTRL, BIN);
FTM1_CNTIN=0x0030; // counter preset value
Serial.print("FTM1_CNTIN: "); Serial.println(FTM1_CNTIN, BIN);
FTM1_CNT = 0x0000; //preset count to 'CNTIN' value by writing to the register
Serial.print("FTM1_CNT: "); Serial.println(FTM1_CNT, BIN); // show counter value gets 'preset'
FTM1_CNTIN=0x0000; // different preset value
FTM1_CNT = 0x0000;
FTM1_MOD = 0xFFFF; //max modulus = 65535 (gives count = 65535 on roll-over)
Serial.print("FTM1_MOD: "); Serial.println(FTM1_MOD, BIN);
// FTM1_C0SC = 0x04; // CHF=0, CHIE=0 (disable interrupt, use software polling), MSB=0 MSA=0, ELSB=0 ELSA=1 (input capture - rising edge), 0, DMA=0
Serial.print("FTM1_C0SC: "); Serial.println(FTM1_C0SC, BIN); // status register ? ?
Serial.print("FTM1_C0V: "); Serial.println(FTM1_C0V, BIN); // aparently the counter values can be pipelined ? ?
Serial.print("FTM1_C1SC: "); Serial.println(FTM1_C1SC, BIN);
//configure Teensy port pins
PORTA_PCR12 |= 0x700; //MUX = alternative function 7 on Chip Pin 28 (FTM1_QD_PHA) = Teensy Pin 3
PORTA_PCR13 |= 0x700; //MUX = alternative function 7 on Chip Pin 29 (FTM1_QD_PHB) = Teensy Pin 4
// remove this ^^^ causes counter to decrement.
PORTB_PCR0 |= 0x300; //MUX = alternative function 3 on Chip Pin 35 (FTM1_CH0) = Teensy Pin 16
}
//(3) main loop statements
void loop() {
for (x=0; x<1023; x++) { // use 'blink' example to make clock pulses
digitalWrite(LED_PIN, HIGH); // this routine makes 25 pulses
delay(5);
digitalWrite(LED_PIN,LOW);
delay(5);
}
//read FTM1 Ch0 value -- just read it to see if value present
p1=FTM1_CNT; //read CH0 COUNTER value
Serial.print("FTM1_CNT: ");
Serial.print(p1, BIN); Serial.print(" ");
Serial.println(p1);
Serial.println();
}This is my output.
Code:
FTM1_MODE: 101
FTM1_SC: 10001001
FTM1_SC: 0
FTM1_QDCTRL: 1001
FTM1_CNTIN: 110000
FTM1_CNT: 110000
FTM1_MOD: 1000111111111111
FTM1_C0SC: 101000
FTM1_C0V: 0
FTM1_C1SC: 101000
FTM1_CNT: 1111111111 1023
FTM1_CNT: 11111111110 2046
FTM1_CNT: 101111111101 3069
FTM1_CNT: 111111111100 4092
FTM1_CNT: 1001111111011 5115
FTM1_CNT: 1011111111010 6138
FTM1_CNT: 1101111111001 7161
FTM1_CNT: 1111111111000 8184
FTM1_CNT: 10001111110111 9207
FTM1_CNT: 10011111110110 10230
FTM1_CNT: 10101111110101 11253
FTM1_CNT: 10111111110100 12276
FTM1_CNT: 11001111110011 13299
FTM1_CNT: 11011111110010 14322
FTM1_CNT: 11101111110001 15345
FTM1_CNT: 11111111110000 16368
FTM1_CNT: 100001111101111 17391
FTM1_CNT: 100011111101110 18414
FTM1_CNT: 100101111101101 19437
FTM1_CNT: 100111111101100 20460
FTM1_CNT: 101001111101011 21483
FTM1_CNT: 101011111101010 22506
FTM1_CNT: 101101111101001 23529
FTM1_CNT: 101111111101000 24552
FTM1_CNT: 110001111100111 25575
FTM1_CNT: 110011111100110 26598
FTM1_CNT: 110101111100101 27621
FTM1_CNT: 110111111100100 28644
FTM1_CNT: 111001111100011 29667
FTM1_CNT: 111011111100010 30690
FTM1_CNT: 111101111100001 31713
FTM1_CNT: 111111111100000 32736
FTM1_CNT: 1000001111011111 33759
FTM1_CNT: 1000011111011110 34782
FTM1_CNT: 1000101111011101 35805
FTM1_CNT: 1000111111011100 36828
FTM1_CNT: 1111011011 987
FTM1_CNT: 11111011010 2010
FTM1_CNT: 101111011001 3033
FTM1_CNT: 111111011000 4056
