use TCC0 at 20kHz PWM

serialstep/serialstep-DRV8428P/README.md

@@ -12,6 +12,17 @@ This is a variant based on the DRV8428P which is a dual H-bridge chip in the DRV
 
 ## Microstepping
 
-Microstepping involves applying PWM on the H-bridges inputs, this is still under development. A quick test showed 732Hz is too slow; the motor vibrates when any sort of load is applied. A higher frequency should be feasible by decreasing TCC0's counter. For 20kHz, a counter of 2400 (instead of 0xFFFF) should be ok with TCC0 in 16-bit mode. Pins PA8, PA9, PA14 and PA15 can all be MUXed to TCC0's outputs with proper settings.
-
 <img src="microstep.mp4" width="100%">
+
+Microstepping up to 32 is achieved through PWM on the H-bridge inputs. A high frequency is needed, therefore 4 channels of TCC0 are used:
+
+| Pin  | TCC0 channel | MUX |
+|------|--------------|-----|
+| PA8  |      2       |  E  |
+| PA8  |      3       |  E  |
+| PA14 |      0       |  F  |
+| PA15 |      1       |  F  |
+
+TCC0 is then setup in normal PWM mode with a period of 2400, yielding 20kHz with a prescaler of 1. This is more than 11 bits of resolution for a nice, smooth sine signal on each of the PWM inputs:
+
+<img src="img/pwm_lookup.png" width="100%">

serialstep/serialstep-DRV8428P/py/sine_tables.py

@@ -4,7 +4,7 @@ import matplotlib.pyplot as plt
 
 
 def main():
-    peak = 4095
+    peak = 2400
     n_micro = 32
 
     # 4 phase cycle
@@ -12,12 +12,16 @@ def main():
     i = np.arange(n_tot)
     theta = i * 2 * math.pi/n_tot
     table_ideal = peak * np.sin(theta)
+    table_ideal[2 * n_micro:] = 0
     table = np.round(table_ideal).astype(np.int32)
-    table[2 * n_micro:] = 0
 
     plt.figure()
     plt.plot(table_ideal, "b")
     plt.step(table, "r")
+    plt.title("xIN PWM lookup")
+    plt.xlabel("index")
+    plt.ylabel("value")
+    plt.legend(["ideal", "quantized"])
     plt.show()
 
     print("int sine_table[] = {")

serialstep/serialstep-DRV8428P/serialstep-DRV8428P.ino

@@ -12,31 +12,45 @@
 // warranty is provided, and users accept all liability.
 //
 
-#define INCR_MOD(a, b, c) ((a+b)%c)
-
+// pins
 #define LEDA 4
 #define LEDC 2
-
 #define NSLEEP 5
 #define AIN1 8
 #define AIN2 9
 #define BIN1 14
 #define BIN2 15
 #define BUTTON 31
-#define BLINK 100
+
+// TCC0 channels
+#define AIN1_CH 2
+#define AIN2_CH 3
+#define BIN1_CH 0
+#define BIN2_CH 1
+
+// peripherals
+#define AIN1_PER PER_TIMER
+#define AIN2_PER PER_TIMER
+#define BIN1_PER PER_TIMER_ALT
+#define BIN2_PER PER_TIMER_ALT
+
+// any power of 2 <= TABLE_MICROSTEP
+#define MICROSTEP 32
 
 // constants
 #define TABLE_MICROSTEP 32
 #define CYCLE 4
+#define TCC0_PERIOD 2400
 #define TABLE_LENGTH (CYCLE*TABLE_MICROSTEP)
 #define TABLE_INCR (TABLE_MICROSTEP/MICROSTEP)
 
-// power of 2, <= TABLE_MICROSTEP
-#define MICROSTEP 2
+// macros
+#define SYNC_TCC0() while (TCC0->SYNCBUSY.reg & TCC_SYNCBUSY_MASK)
+#define INCR_MOD(a, b, c) (((a+b)%c + c) % c)
 
-unsigned int sine_table[] = {
-   0, 201, 401, 601, 799, 995,1189,1380,1567,1751,1930,2105,2275,2439,2598,2750,2896,3034,3165,3289,3405,3512,3611,3702,3783,3856,3919,3972,4016,4051,4075,4090,
-4095,4090,4075,4051,4016,3972,3919,3856,3783,3702,3611,3512,3405,3289,3165,3034,2896,2750,2598,2439,2275,2105,1930,1751,1567,1380,1189, 995, 799, 601, 401, 201,
+uint16_t sine_table[] = {
+   0, 118, 235, 352, 468, 583, 697, 809, 918,1026,1131,1234,1333,1430,1523,1612,1697,1778,1855,1928,1996,2059,2117,2170,2217,2260,2297,2328,2354,2374,2388,2397,
+2400,2397,2388,2374,2354,2328,2297,2260,2217,2170,2117,2059,1996,1928,1855,1778,1697,1612,1523,1430,1333,1234,1131,1026, 918, 809, 697, 583, 468, 352, 235, 118,
    0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
    0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0
 };
@@ -47,6 +61,48 @@ int count_A2 = 2*TABLE_MICROSTEP;
 int count_B1 = TABLE_MICROSTEP;
 int count_B2 = 3*TABLE_MICROSTEP;
 
+void setup_peripheral(uint8_t pinNum, EPioPeripheral peripheral) {
+    uint8_t pinCfg = (PORT->Group[PORTA].PINCFG[pinNum].reg & PORT_PINCFG_PULLEN);
+    if ( pinNum & 1 ) { // odd pin
+        uint32_t temp = (PORT->Group[PORTA].PMUX[pinNum >> 1].reg) & PORT_PMUX_PMUXE( 0xF ) ;
+        PORT->Group[PORTA].PMUX[pinNum >> 1].reg = temp|PORT_PMUX_PMUXO( peripheral ) ;
+    } else { // even pin
+        uint32_t temp = (PORT->Group[PORTA].PMUX[pinNum >> 1].reg) & PORT_PMUX_PMUXO( 0xF ) ;
+        PORT->Group[PORTA].PMUX[pinNum >> 1].reg = temp|PORT_PMUX_PMUXE( peripheral ) ;
+    }
+    pinCfg |= PORT_PINCFG_PMUXEN; // Enable peripheral mux
+    PORT->Group[PORTA].PINCFG[pinNum].reg = (uint8_t)pinCfg;
+}
+
+void setup_timer() {
+   setup_peripheral(BIN1, BIN1_PER);
+   setup_peripheral(BIN2, BIN2_PER);
+   setup_peripheral(AIN1, AIN1_PER);
+   setup_peripheral(AIN2, AIN2_PER);
+
+   GCLK->CLKCTRL.reg = (uint16_t) (GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN_GCLK0 | GCM_TCC0) ;
+   while ( GCLK->STATUS.bit.SYNCBUSY == 1 );
+
+   TCC0->CTRLA.bit.ENABLE = 0;
+   SYNC_TCC0();
+   TCC0->WAVE.reg |= TCC_WAVE_WAVEGEN_NPWM;
+   SYNC_TCC0();
+
+   TCC0->PER.reg = TCC0_PERIOD;
+   SYNC_TCC0();
+   TCC0->CTRLA.bit.ENABLE = 1;
+   SYNC_TCC0();
+   }
+
+void update_pwm(int timerChannel, uint16_t value) {
+   TCC0->CTRLBSET.bit.LUPD = 1;
+   SYNC_TCC0();
+   TCC0->CCB[timerChannel].reg = (uint32_t) value;
+   SYNC_TCC0();
+   TCC0->CTRLBCLR.bit.LUPD = 1;
+   SYNC_TCC0();
+   }
+
 void setup() {
    SerialUSB.begin(0);
    digitalWrite(LEDA,HIGH);
@@ -55,17 +111,10 @@ void setup() {
    pinMode(LEDC,OUTPUT);
    digitalWrite(NSLEEP,HIGH);
    pinMode(NSLEEP,OUTPUT);
-   digitalWrite(AIN1,LOW);
-   pinMode(AIN1,OUTPUT);
-   digitalWrite(AIN2,LOW);
-   pinMode(AIN2,OUTPUT);
-   digitalWrite(BIN1,LOW);
-   pinMode(BIN1,OUTPUT);
-   digitalWrite(BIN2,LOW);
-   pinMode(BIN2,OUTPUT);
    pinMode(BUTTON, INPUT_PULLUP);
-   // 10-bit PWM
-   analogWriteResolution(12);
+
+   // init TCC0 and enable outputs
+   setup_timer();
    // init stepping
    step(0);
    }
@@ -77,10 +126,11 @@ void step(int val) {
    count_A2 = INCR_MOD(count_A2, val_incr, TABLE_LENGTH);
    count_B1 = INCR_MOD(count_B1, val_incr, TABLE_LENGTH);
    count_B2 = INCR_MOD(count_B2, val_incr, TABLE_LENGTH);
-   analogWrite(AIN1, sine_table[count_A1]);
-   analogWrite(AIN2, sine_table[count_A2]);
-   analogWrite(BIN1, sine_table[count_B1]);
-   analogWrite(BIN2, sine_table[count_B2]);
+
+   update_pwm(AIN1_CH, sine_table[count_A1]);
+   update_pwm(AIN2_CH, sine_table[count_A2]);
+   update_pwm(BIN1_CH, sine_table[count_B1]);
+   update_pwm(BIN2_CH, sine_table[count_B2]);
    }