2ca67fc36b
* Fix pulseIn() on SAMD51 by writing it in plain C, so that the CM0+-specific pulse_asm won't need to be linked. The SAMD51 is fast enough that we can time pulses with micros() Tested with a bunch of pulse lengths from <1us to >1s * Implement a new delayMicroseconds() function for SAMD51 This version enables the "Debug Watchpoint and Trace" module (DWT) in startup.c and then uses the 32bit cycle counter that is part of DWT to count cycles indepenent of instruction timing. Tested for good accuracy with various values between 1 and 2000us.
109 lines
3.5 KiB
C
109 lines
3.5 KiB
C
/*
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Copyright (c) 2015 Arduino LLC. All right reserved.
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SAMD51 support added by Adafruit - Copyright (c) 2018 Dean Miller for Adafruit Industries
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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See the GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef _DELAY_
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#define _DELAY_
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#include <stdint.h>
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#include "variant.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* \brief Returns the number of milliseconds since the Arduino board began running the current program.
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*
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* This number will overflow (go back to zero), after approximately 50 days.
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*
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* \return Number of milliseconds since the program started (uint32_t)
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*/
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extern unsigned long millis( void ) ;
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/**
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* \brief Returns the number of microseconds since the Arduino board began running the current program.
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*
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* This number will overflow (go back to zero), after approximately 70 minutes. On 16 MHz Arduino boards
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* (e.g. Duemilanove and Nano), this function has a resolution of four microseconds (i.e. the value returned is
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* always a multiple of four). On 8 MHz Arduino boards (e.g. the LilyPad), this function has a resolution
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* of eight microseconds.
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*
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* \note There are 1,000 microseconds in a millisecond and 1,000,000 microseconds in a second.
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*/
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extern unsigned long micros( void ) ;
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/**
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* \brief Pauses the program for the amount of time (in miliseconds) specified as parameter.
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* (There are 1000 milliseconds in a second.)
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*
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* \param dwMs the number of milliseconds to pause (uint32_t)
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*/
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extern void delay( unsigned long dwMs ) ;
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/**
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* \brief Pauses the program for the amount of time (in microseconds) specified as parameter.
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*
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* \param dwUs the number of microseconds to pause (uint32_t)
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*/
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#if defined(__SAMD51__)
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extern void delayMicroseconds( unsigned int );
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#else
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static __inline__ void delayMicroseconds( unsigned int ) __attribute__((always_inline, unused)) ;
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static __inline__ void delayMicroseconds( unsigned int usec )
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{
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if ( usec == 0 )
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{
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return ;
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}
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/*
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* The following loop:
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*
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* for (; ul; ul--) {
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* __asm__ volatile("");
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* }
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*
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* produce the following assembly code:
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*
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* loop:
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* subs r3, #1 // 1 Core cycle
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* bne.n loop // 1 Core cycle + 1 if branch is taken
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*/
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// VARIANT_MCK / 1000000 == cycles needed to delay 1uS
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// 3 == cycles used in a loop
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uint32_t n = usec * (VARIANT_MCK / 1000000) / 3;
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__asm__ __volatile__(
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"1: \n"
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" sub %0, #1 \n" // substract 1 from %0 (n)
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" bne 1b \n" // if result is not 0 jump to 1
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: "+r" (n) // '%0' is n variable with RW constraints
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: // no input
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: // no clobber
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);
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// https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
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// https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Volatile
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}
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#endif
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#ifdef __cplusplus
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}
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#endif
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#endif /* _DELAY_ */
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