PWM for GSClk not working on SAMD (Arduino Nano IOT)

[97Cweb]

Hello William
I just reached out to you on Arduino forums as well. I don't know how to fork but here is the code for making a GSClk on pin 9 for nanos.

`
// this function may be a source of trouble if
// GSCLK default frequency is too low (3KHz is around the minimum)
inline void Tlc5948::startBuiltinGsclk() {
// Number to count to with PWM (TOP value). Frequency can be calculated by
// freq = GCLK4_freq / (TCC0_prescaler * (1 + TOP_value))
// With TOP of 47, we get a 1 MHz square wave in this example

//freq = 48 / (1 * (1+top))
//freq out should be 8
//8 = 48 / (1 * (1+top))
//8 * (1 + top) = 48
//1 + top = 6
//top = 5
uint32_t period = 6 - 1;

// Because we are using TCC0, limit period to 24 bits
period = ( period < 0x00ffffff ) ? period : 0x00ffffff;

// Enable and configure generic clock generator 4
GCLK->GENCTRL.reg = GCLK_GENCTRL_IDC | // Improve duty cycle
GCLK_GENCTRL_GENEN | // Enable generic clock gen
GCLK_GENCTRL_SRC_DFLL48M | // Select 48MHz as source
GCLK_GENCTRL_ID(4); // Select GCLK4
while (GCLK->STATUS.bit.SYNCBUSY); // Wait for synchronization

// Set clock divider of 1 to generic clock generator 4
GCLK->GENDIV.reg = GCLK_GENDIV_DIV(1) | // Divide 48 MHz by 1
GCLK_GENDIV_ID(4); // Apply to GCLK4 4
while (GCLK->STATUS.bit.SYNCBUSY); // Wait for synchronization

// Enable GCLK4 and connect it to TCC0 and TCC1
GCLK->CLKCTRL.reg = GCLK_CLKCTRL_CLKEN | // Enable generic clock
GCLK_CLKCTRL_GEN_GCLK4 | // Select GCLK4
GCLK_CLKCTRL_ID_TCC0_TCC1; // Feed GCLK4 to TCC0/1
while (GCLK->STATUS.bit.SYNCBUSY); // Wait for synchronization

// Divide counter by 1 giving 48 MHz (20.83 ns) on each TCC0 tick
TCC0->CTRLA.reg |= TCC_CTRLA_PRESCALER(TCC_CTRLA_PRESCALER_DIV1_Val);

// Use "Normal PWM" (single-slope PWM): count up to PER, match on CC[n]
TCC0->WAVE.reg = TCC_WAVE_WAVEGEN_NPWM; // Select NPWM as waveform
while (TCC0->SYNCBUSY.bit.WAVE); // Wait for synchronization

// Set the period (the number to count to (TOP) before resetting timer)
TCC0->PER.reg = period;
while (TCC0->SYNCBUSY.bit.PER);

// Set PWM signal to output 50% duty cycle
// n for CC[n] is determined by n = x % 4 where x is from WO[x]
TCC0->CC[2].reg = period / 2;
while (TCC0->SYNCBUSY.bit.CC2);

// Configure PA20 (D9 on Arduino Nano) to be output
PORT->Group[PORTA].DIRSET.reg = PORT_PA20; // Set pin as output
PORT->Group[PORTA].OUTCLR.reg = PORT_PA20; // Set pin to low

// Enable the port multiplexer for PA18
PORT->Group[PORTA].PINCFG[20].reg |= PORT_PINCFG_PMUXEN;

// Connect TCC0 timer to PA18. Function F is TCC0/WO[2] for PA18.
// Odd pin num (2n + 1): use PMUXO
// Even pin num (2n): use PMUXE
PORT->Group[PORTA].PMUX[10].reg = PORT_PMUX_PMUXE_F;

// Enable output (start PWM)
TCC0->CTRLA.reg |= (TCC_CTRLA_ENABLE);
while (TCC0->SYNCBUSY.bit.ENABLE); // Wait for synchronization
}
`

[97Cweb]

If you want to read more, it is based heavily off of https://shawnhymel.com/1710/arduino-zero-samd21-raw-pwm-using-cmsis/