Hi @meso2
The code that you link to, is quite old. Initially, I used the attachInterrupt() function for expediency, as it didn't require any register set-up. However, it eventually dawned on me that this function was unnecessarily calling the EIC_Handler() interrupt service routine for each input pulse, even with the function pointer set to NULL, greatly slowing down the CPU for high frequency signals.
Nowadays, I just set-up the interrupt EIC (External Interrupt Controller) module using registers and thereby allow the input signal to pass to the timer with EIC interrupts turned off.
Anyway, here's the code for timer TC4 pulse width and period capture on PA10 (D2) for the Seeeeeeeduino XIAO:
// Setup TC4 to capture pulse-width and period on digital pin D2 on Seeeduino Xiao
volatile boolean periodComplete;
volatile uint32_t isrPeriod;
volatile uint32_t isrPulsewidth;
uint32_t period;
uint32_t pulsewidth;
void setup() {
SerialUSB.begin(115200); // Initialise the native serial port
while(!SerialUSB); // Wait for the console to open
PM->APBCMASK.reg |= PM_APBCMASK_EVSYS; // Switch on the event system peripheral
GCLK->GENDIV.reg = GCLK_GENDIV_DIV(1) | // Divide the 48MHz system clock by 1 = 48MHz
GCLK_GENDIV_ID(4); // Set division on Generic Clock Generator (GCLK) 4
GCLK->GENCTRL.reg = GCLK_GENCTRL_IDC | // Set the duty cycle to 50/50 HIGH/LOW
GCLK_GENCTRL_GENEN | // Enable GCLK 4
GCLK_GENCTRL_SRC_DFLL48M | // Set the clock source to 48MHz
GCLK_GENCTRL_ID(4); // Set clock source on GCLK 4
while (GCLK->STATUS.bit.SYNCBUSY); // Wait for synchronization
GCLK->CLKCTRL.reg = GCLK_CLKCTRL_CLKEN | // Route GCLK4 to TC4 and TC5
GCLK_CLKCTRL_GEN_GCLK4 |
GCLK_CLKCTRL_ID_TC4_TC5;
// Enable the port multiplexer on port pin PA10
PORT->Group[PORTA].PINCFG[10].bit.PMUXEN = 1;
// Set-up the pin as an EIC (interrupt) on port pin PA10
PORT->Group[PORTA].PMUX[10 >> 1].reg |= PORT_PMUX_PMUXE_A;
EIC->EVCTRL.reg |= EIC_EVCTRL_EXTINTEO10; // Enable event output on external interrupt 10
EIC->CONFIG[1].reg |= EIC_CONFIG_SENSE2_HIGH; // Set event detecting a HIGH level
EIC->INTENCLR.reg = EIC_INTENCLR_EXTINT10; // Disable interrupts on external interrupt 10
EIC->CTRL.reg |= EIC_CTRL_ENABLE; // Enable EIC peripheral
while (EIC->STATUS.bit.SYNCBUSY); // Wait for synchronization
EVSYS->USER.reg = EVSYS_USER_CHANNEL(1) | // Attach the event user (receiver) to channel 0 (n + 1)
EVSYS_USER_USER(EVSYS_ID_USER_TC4_EVU); // Set the event user (receiver) as timer TC4
EVSYS->CHANNEL.reg = EVSYS_CHANNEL_EDGSEL_NO_EVT_OUTPUT | // No event edge detection
EVSYS_CHANNEL_PATH_ASYNCHRONOUS | // Set event path as asynchronous
EVSYS_CHANNEL_EVGEN(EVSYS_ID_GEN_EIC_EXTINT_10) | // Set event generator (sender) as external interrupt 10
EVSYS_CHANNEL_CHANNEL(0); // Attach the generator (sender) to channel 0
TC4->COUNT32.EVCTRL.reg = TC_EVCTRL_TCEI | // Enable the TC event input
//TC_EVCTRL_TCINV | // Invert the event input
TC_EVCTRL_EVACT_PPW; // Set up the timer for capture: CC0 period, CC1 pulsewidth
TC4->COUNT32.CTRLC.reg = TC_CTRLC_CPTEN1 | // Enable capture on CC1
TC_CTRLC_CPTEN0; // Enable capture on CC0
while (TC4->COUNT32.STATUS.bit.SYNCBUSY); // Wait for synchronization
NVIC_SetPriority(TC4_IRQn, 0); // Set the Nested Vector Interrupt Controller (NVIC) priority for TC4 to 0 (highest)
NVIC_EnableIRQ(TC4_IRQn); // Connect the TC4 timer to the Nested Vector Interrupt Controller (NVIC)
TC4->COUNT32.INTENSET.reg = TC_INTENSET_MC1 | // Enable compare channel 1 (CC1) interrupts
TC_INTENSET_MC0; // Enable compare channel 0 (CC0) interrupts
TC4->COUNT32.CTRLA.reg = //TC_CTRLA_PRESCSYNC_PRESC | // Overflow on precaler clock, (rather than the GCLK)
TC_CTRLA_PRESCALER_DIV1 | // Set prescaler to 1, 48MHz/1 = 48MHz
TC_CTRLA_MODE_COUNT32; // Set TC4/TC5 to 32-bit timer mode
TC4->COUNT32.CTRLA.bit.ENABLE = 1; // Enable TC4
while (TC4->COUNT32.STATUS.bit.SYNCBUSY); // Wait for synchronization
}
void loop() {
if (periodComplete) // Check if the period is complete
{
noInterrupts(); // Read the new period and pulse-width
period = isrPeriod;
pulsewidth = isrPulsewidth;
interrupts();
SerialUSB.print("PW: ");
SerialUSB.print(pulsewidth);
SerialUSB.print(F(" "));
SerialUSB.print("P: ");
SerialUSB.println(period);
periodComplete = false; // Start a new period
}
}
void TC4_Handler() // Interrupt Service Routine (ISR) for timer TC4
{
// Check for match counter 0 (MC0) interrupt
if (TC4->COUNT32.INTFLAG.bit.MC0)
{
TC4->COUNT32.READREQ.reg = TC_READREQ_RREQ | // Enable a read request
TC_READREQ_ADDR(0x18); // Offset address of the CC0 register
while (TC4->COUNT32.STATUS.bit.SYNCBUSY); // Wait for (read) synchronization
isrPeriod = TC4->COUNT32.CC[0].reg; // Copy the period
periodComplete = true; // Indicate that the period is complete
}
// Check for match counter 1 (MC1) interrupt
if (TC4->COUNT32.INTFLAG.bit.MC1)
{
TC4->COUNT32.READREQ.reg = TC_READREQ_RREQ | // Enable a read request
TC_READREQ_ADDR(0x1A); // Offset address of the CC1 register
while (TC4->COUNT32.STATUS.bit.SYNCBUSY); // Wait for (read) synchronization
isrPulsewidth = TC4->COUNT32.CC[1].reg; // Copy the pulse-width
}
}