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https://github.com/Valeh2012/PersonalVotingMachine
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130 lines
3.6 KiB
C
130 lines
3.6 KiB
C
/*
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delay.c
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The delay function delay_micro_seconds() will use the global variable
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SystemCoreClock. A call to SystemCoreClockUpdate() is required before
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using delay_micro_seconds().
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STM32L031 Project (U8g2 Library)
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Copyright (c) 2017, olikraus@gmail.com
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All rights reserved.
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Redistribution and use in source and binary forms, with or without modification,
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are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright notice, this list
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of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright notice, this
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list of conditions and the following disclaimer in the documentation and/or other
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materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "stm32l031xx.h"
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/* Generic ARM delay procedure, based on the system timer (SysTick) */
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/*
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Delay by the provided number of system ticks.
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The delay must be smaller than the RELOAD value.
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This delay has an imprecision of about +/- 20 system ticks.
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*/
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static void _delay_system_ticks_sub(uint32_t sys_ticks)
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{
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uint32_t start_val, end_val, curr_val;
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uint32_t load;
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start_val = SysTick->VAL;
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start_val &= 0x0ffffffUL;
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end_val = start_val;
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if ( end_val < sys_ticks )
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{
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/* check, if the operation after this if clause would lead to a negative result */
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/* if this would be the case, then add the reload value first */
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load = SysTick->LOAD;
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load &= 0x0ffffffUL;
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end_val += load;
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}
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/* counter goes towards zero, so end_val is below start value */
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end_val -= sys_ticks;
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/* wait until interval is left */
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if ( start_val >= end_val )
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{
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for(;;)
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{
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curr_val = SysTick->VAL;
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curr_val &= 0x0ffffffUL;
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if ( curr_val <= end_val )
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break;
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if ( curr_val > start_val )
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break;
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}
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}
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else
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{
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for(;;)
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{
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curr_val = SysTick->VAL;
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curr_val &= 0x0ffffffUL;
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if ( curr_val <= end_val && curr_val > start_val )
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break;
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}
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}
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}
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/*
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Delay by the provided number of system ticks.
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Any values between 0 and 0x0ffffffff are allowed.
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*/
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void delay_system_ticks(uint32_t sys_ticks)
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{
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uint32_t load4;
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load4 = SysTick->LOAD;
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load4 &= 0x0ffffffUL;
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load4 >>= 2;
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while ( sys_ticks > load4 )
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{
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sys_ticks -= load4;
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_delay_system_ticks_sub(load4);
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}
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_delay_system_ticks_sub(sys_ticks);
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}
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/*
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Delay by the provided number of micro seconds.
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Limitation: "us" * System-Freq in MHz must not overflow in 32 bit.
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Values between 0 and 1.000.000 (1 second) are ok.
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Important: Call SystemCoreClockUpdate() before calling this function.
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*/
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void delay_micro_seconds(uint32_t us)
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{
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uint32_t sys_ticks;
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sys_ticks = SystemCoreClock;
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sys_ticks /=1000000UL;
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sys_ticks *= us;
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delay_system_ticks(sys_ticks);
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}
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