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.
117 lines
3.1 KiB
C
117 lines
3.1 KiB
C
/*
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Copyright (c) 2015 Arduino LLC. All right reserved.
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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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#include "delay.h"
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#include "Arduino.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/** Tick Counter united by ms */
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static volatile uint32_t _ulTickCount=0 ;
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unsigned long millis( void )
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{
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// todo: ensure no interrupts
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return _ulTickCount ;
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}
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// Interrupt-compatible version of micros
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// Theory: repeatedly take readings of SysTick counter, millis counter and SysTick interrupt pending flag.
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// When it appears that millis counter and pending is stable and SysTick hasn't rolled over, use these
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// values to calculate micros. If there is a pending SysTick, add one to the millis counter in the calculation.
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unsigned long micros( void )
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{
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uint32_t ticks, ticks2;
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uint32_t pend, pend2;
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uint32_t count, count2;
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ticks2 = SysTick->VAL;
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pend2 = !!(SCB->ICSR & SCB_ICSR_PENDSTSET_Msk) ;
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count2 = _ulTickCount ;
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do
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{
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ticks=ticks2;
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pend=pend2;
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count=count2;
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ticks2 = SysTick->VAL;
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pend2 = !!(SCB->ICSR & SCB_ICSR_PENDSTSET_Msk) ;
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count2 = _ulTickCount ;
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} while ((pend != pend2) || (count != count2) || (ticks < ticks2));
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return ((count+pend) * 1000) + (((SysTick->LOAD - ticks)*(1048576/(VARIANT_MCK/1000000)))>>20) ;
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// this is an optimization to turn a runtime division into two compile-time divisions and
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// a runtime multiplication and shift, saving a few cycles
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}
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#ifdef __SAMD51__
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/*
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* On SAMD51, use the (32bit) cycle count maintained by the DWT unit,
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* and count exact number of cycles elapsed, rather than guessing how
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* many cycles a loop takes, which is dangerous in the presence of
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* cache. The overhead of the call and internal code is "about" 20
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* cycles. (at 120MHz, that's about 1/6 us)
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*/
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void delayMicroseconds(unsigned int us)
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{
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uint32_t start, elapsed;
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uint32_t count;
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if (us == 0)
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return;
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count = us * (VARIANT_MCK / 1000000) - 20; // convert us to cycles.
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start = DWT->CYCCNT; //CYCCNT is 32bits, takes 37s or so to wrap.
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while (1) {
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elapsed = DWT->CYCCNT - start;
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if (elapsed >= count)
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return;
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}
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}
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#endif
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void delay( unsigned long ms )
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{
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if ( ms == 0 )
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{
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return ;
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}
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uint32_t start = _ulTickCount ;
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do
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{
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yield() ;
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} while ( _ulTickCount - start < ms ) ;
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}
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#include "Reset.h" // for tickReset()
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void SysTick_DefaultHandler(void)
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{
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// Increment tick count each ms
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_ulTickCount++;
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tickReset();
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}
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#ifdef __cplusplus
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}
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#endif
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