unsignedlongpulseIn(uint8_tpin,uint8_tstate,unsignedlongtimeout){// cache the port and bit of the pin in order to speed up the
// pulse width measuring loop and achieve finer resolution. calling
// digitalRead() instead yields much coarser resolution.
uint8_tbit=digitalPinToBitMask(pin);uint8_tport=digitalPinToPort(pin);uint8_tstateMask=(state?bit:0);// convert the timeout from microseconds to a number of times through
// the initial loop; it takes approximately 16 clock cycles per iteration
unsignedlongmaxloops=microsecondsToClockCycles(timeout)/16;unsignedlongwidth=countPulseASM(portInputRegister(port),bit,stateMask,maxloops);// prevent clockCyclesToMicroseconds to return bogus values if countPulseASM timed out
if(width)returnclockCyclesToMicroseconds(width*16+16);elsereturn0;}
// cache the port and bit of the pin in order to speed up the
// pulse width measuring loop and achieve finer resolution. calling
// digitalRead() instead yields much coarser resolution.
uint8_tbit=digitalPinToBitMask(pin);uint8_tport=digitalPinToPort(pin);
stateMaskとmaxloopsを設定します。
8
9
10
11
12
uint8_tstateMask=(state?bit:0);// convert the timeout from microseconds to a number of times through
// the initial loop; it takes approximately 16 clock cycles per iteration
unsignedlongmaxloops=microsecondsToClockCycles(timeout)/16;
// prevent clockCyclesToMicroseconds to return bogus values if countPulseASM timed out
if(width)returnclockCyclesToMicroseconds(width*16+16);elsereturn0;}