I use TCB's single shot mode. The datasheet says that there is a 2 clock delay from the trigger event to the start of the count.(2 to 3 clocks are written elsewhere)
But in reality it is 4 clocks.
The devices I tested were mega3208, mega4809 and tiny1616, but the results were the same.
Is this my mistake?
Please give me your opinion.
This is the test code for mega0.
Generate a single shot of 4 clock width.
#include <avr/io.h>
#include <avr/interrupt.h>
////////////////////////////////////////////////////////////////
// Fuses
////////////////////////////////////////////////////////////////
FUSES = {
.WDTCFG = 0,
.BODCFG = 0,
.OSCCFG = FUSE_FREQSEL1_bm, // 20MHz
.SYSCFG1 = 0b00000111,
.APPEND = 0,
.BOOTEND = 0,
.SYSCFG0 = 0b11000000,
};
////////////////////////////////////////////////////////////////
// main
////////////////////////////////////////////////////////////////
int main(void){
// CLOCK set(20MHz)
_PROTECTED_WRITE((CLKCTRL.MCLKCTRLB), CLKCTRL_PDIV_2X_gc | !CLKCTRL_PEN_bm);
_PROTECTED_WRITE((CLKCTRL.MCLKCTRLA), CLKCTRL_CLKSEL_OSC20M_gc);
EVSYS.CHANNEL0 = EVSYS_GENERATOR_TCB1_CMP0_gc;
EVSYS.USERTCB0 = EVSYS_CHANNEL_CHANNEL0_gc;
EVSYS.USEREVOUTB = EVSYS_CHANNEL_CHANNEL0_gc;
// TCB1 1ms Periodic (TCB0 trigger)
TCB1.CCMP = 20 * 1000 -1;
TCB1.CTRLB = TCB_CNTMODE_INT_gc;
TCB1.CTRLA = TCB_CLKSEL_CLKDIV1_gc | TCB_ENABLE_bm;
// TCB0 4clk width 1shot
TCB0.CCMP = TCB0.CNT = 3;
TCB0.EVCTRL = TCB_CAPTEI_bm;
// TEST parameter
TCB0.CTRLB = TCB_CNTMODE_SINGLE_gc | TCB_CCMPEN_bm;
// TCB0.CTRLB = TCB_CNTMODE_SINGLE_gc | TCB_CCMPEN_bm | TCB_ASYNC_bm;
TCB0.CTRLA = TCB_CLKSEL_CLKDIV1_gc | TCB_ENABLE_bm;
// TCB0.CTRLA = TCB_CLKSEL_CLKDIV_gc | TCB_ENABLE_bm;
sei();
while (1) {
}
}
This is the output waveform.
You can see that it takes 4 clocks to start up single shot.
This is the output waveform in asynchronous mode.
The event is received without delay and the output is transitioning to H immediately.
